WO2005055660A2

WO2005055660A2 - Panel heating element and method for the production thereof

Info

Publication number: WO2005055660A2
Application number: PCT/AT2004/000422
Authority: WO
Inventors: Christian Haider
Original assignee: Econ Export + Consulting Group Gmbh
Priority date: 2003-12-04
Filing date: 2004-12-02
Publication date: 2005-06-16
Also published as: EP1730995A2; AT7326U1; WO2005055660A3

Abstract

The invention relates to a method for producing a panel heating element as a resistance heater with a multilayer structure. Said panel heating element converts delivered electric power into thermal energy and transfers the same to a supporting material (1) that is provided with a planar, curved, or multidimensionally shaped surface. The inventive method is characterized in that the heat-generating electrical conductor (3) is applied to the supporting material that is to be heated by means of a screen printing process and is dried, whereupon the electrical conductor (3) is covered with a plastic-based insulating layer (2) by means of a screen printing, spraying, or rolling-on process, and the insulating layer (2) is dried and cured at maximum temperatures of 300 °C. The invention also relates to a panel heating element that is produced according to the disclosed method.

Description

Surface heating element and process for its manufacture

The present invention relates to a method for producing a surface heating element as a resistance heater in a multilayer structure, which converts electrical energy supplied into heat energy and emits it to a carrier material, the carrier material having a flat, curved or a multidimensionally shaped surface.

Several methods for producing surface heating elements are known from the literature. No. 4,203,198 A describes the production of a surface heating element in which a thin metal foil is embedded between two layers of glass fiber mats and the entire sandwich arrangement is fixed with a temperature-resistant binder. The binder contains colloidally bound silicon particles. The glass fiber layers serve as a base, top and insulation layer, and the metal foil forms the resistance heating element.

DE 21 51 626 A calls a method for producing a rigid, heatable surface heating element, which consists of a thin, heat-resistant, rigid, heat-emitting layer, which has an electrically conductive film with corresponding electrical connections and a thicker, electrically insulating one , rigid layer is connected. To form the electrically conductive film, an aqueous plastic dispersion which contains electrically conductive particles such as noble metals, carbon, soot or graphite and additionally potassium or sodium silicate is applied to the thin, heat-emitting layer. After the aqueous dispersion has dried at temperatures of around 90 ° C., a thicker, heat-insulating layer of rigid polyurethane foam is applied by the foam-forming reaction mixture coming into direct contact with the electrically conductive film.

DE 196 38 640 A discloses a method for producing surface heating elements for ceramic hobs. The heating conductor is separated from a metal foil, for example by punching out or etching out. This film is suspended in the distance between the insulation base plate and the ceramic hob, whereby the effects of thermal expansion, which occur at temperatures of up to 1200 C, can be compensated for by sagging in the air space. DE 100 25 539 A also uses a heating foil with a heating conductor pattern. However, a ceramic-filled polymer layer is arranged between the heating foil and the surface to be heated. The polymer layer connected to the heating foil is pressed with an insulating molded body against the surface to be heated or glued to this surface. The ceramic-filled polymer layer has a very low heat transfer resistance combined with a high electrical insulation capacity. The polymer layer is stable up to about 150 ° C. This heating surface is preferably attached to the outside of a water-filled container. Due to the good heat-conducting connection with the surface to be heated, the heating device remains at comparatively low temperatures.

DE 27 19 174 A describes a method for producing a heatable exterior mirror for motor vehicles, in which a resistance layer made of carbon synthetic resin is printed on an insulating layer and is covered with a further insulating layer made of epoxy resin or silicone rubber. The layers are printed, sprayed or spread using the screen printing process. The power supply electrodes consist of a solderable conductive paste. In addition, the use of carbon-conductive varnishes and the printing using the screen printing process is known. Conductors made of carbon conductive varnish are applied to plastic foils, such as polyimide foils. Such conductor track films can be connected to the component to be heated by gluing.

Furthermore, DE 35 25 488 A describes a heating device for keeping the surface reflector of an antenna free of ice, the use of graphite lacquer as a heating conductor, which is applied using a printing process or by spraying on using a template, being described. The heating power is around 200 to 400 W / m ² . However, this area performance is not sufficient for applications as a warming area or for tempering or heating a container, since heating powers of 0.1 to 30 W / cm ^{2 are} required here.

Furthermore, numerous publications are known about heating devices that are operated with electric current. Depending on the temperature level in the application area, they can be differentiated into high-temperature and low-temperature applications. High temperature resistant materials are required for high temperature applications, which affect temperatures of over 300 ° C. These devices can be used for air heating, for steam generation, for toasters, soldering devices, ironing machines and the like. The low-temperature heating elements are used in the area of surface temperature control, such as hot plates, thawing devices systems, aquarium heaters, mirror and glass heaters, warming devices for gaseous and liquid media and the like.

If the surface to be heated is metallic, an insulation layer is usually arranged between this surface and the heating element. This can consist of enamel, a plasma layer, metal oxide, metal nitrite, insulating adhesive or a plastic layer, such as a plastic film.

Low-temperature elements, such as those used for warming plates, are preferably made from heatable ceramics, from plastic films coated with resistance materials, or from thick-film elements with coatings which are applied by screen printing or by a spraying process.

Heated ceramics have the disadvantage that the mechanical strength is generally very low, but their production is complex and therefore costly. Resistance heating elements, which are produced by etching from a metal foil and then gluing onto a plastic foil or by printing a conductive material onto a plastic foil, have the major disadvantage that bubble-free gluing of the heating element produced in this way is necessary with the carrier. As soon as there are glueing errors or peeling or blistering due to aging, gas-filled areas with poor heat transfer occur and subsequently lead to an overload of the heating element at neighboring points. If a critical value is exceeded, there is an interruption in the conductor and the heating element fails completely.

Heating elements that are manufactured in thick-film technology and in which the dielectric is produced by spraying or by a printing process have the advantage of a direct and permanent connection to the carrier surface, but they usually require firing temperatures above 300 ° C. As a result, in addition to the sintering process of the thick-film pastes, the carrier surface also changes optically. These elements therefore require additional surface treatments such as grinding and polishing. Another disadvantage is that printing is not possible on most plastics and in some cases on aluminum and other non-ferrous metals.

The present invention therefore has as its object a method for producing a heating element with printed or sprayed on To create a dielectric with which a permanent, reliable heating element can be produced on a carrier substance, with which there can be no overheating problems which impair the life of the heating element due to the formation of bubbles, whereby only temperatures below 300 ° C are used in the production process. Furthermore, the application of the heating element to any carrier substance should be made possible and no post-processing such as grinding or polishing should be required.

According to the invention, these objects are achieved in that the heat-generating electrical conductor is applied to the carrier material to be heated by means of a screen printing process and is dried, the electrical conductor is then covered with an insulating layer on a plastic basis by means of a screen printing process or by spraying or rolling, and the insulating layer is added Temperatures of up to 300 ° C are dried and cured.

The proposed use of an insulating varnish or a varnish used in the area of the insulation of electrical components, such as windings, capacitors, electrical casting compounds, which are applied by spraying techniques or by printing techniques such as screen printing or pad printing, makes it possible to produce the insulating layers required for a resistance layer. The use of hardenable solder resists with a temperature resistance of up to 300 ° C has proven to be particularly advantageous here. Due to the bubble-free or low-bubble application on the metallic carrier, the insulation strengths required for the respective heating voltages can be achieved by single or multiple printing or by application using spray technology.

A conductive paste with a defined resistance value is applied to this insulating layer. It is particularly advantageous here to apply carbon-conductive lacquers which have a specific resistance in the range from 1 to 1000 ohms / area unit and are temperature-resistant and resistant to resistance in the required temperature range.

Depending on the required heated surfaces and the resulting performance and resistance value, the printed surface consists of a full-surface design or a sequence of individual conductor tracks, which can consist, for example, of a meandering or spiral shape, but also of alternately thick and thinner conductor tracks. There are no limits to the specific design. The individual pastes are cured at a maximum temperature of 300 ° C. This limitation of the curing temperature does not result in any visible changes in the metallic carrier substance.

The same insulating lacquers can be used for the final protective covering of the heating element, as a result of which a complete enclosure of the electrically conductive structure is achieved.

In this protective cover, those areas are kept free where the power connections are to be made later. The electrical connection can be made, for example, using plug-in tabs that are glued directly onto the electrically conductive heating element with conductive adhesive. Another possibility is, for example, the application of conductive lacquers based on silver or copper or other solderable metals in the area of the connection points. Another option is to attach pegs or strands to the heating element using suitable soldering or welding processes. An alternative possibility is the use of specially designed surface pressure contacts with a surface that is good electrical conductivity and thus ensures safe current transfer.

Known from the prior art NTC and PTC elements, paste prints or connecting lines, as well as mechanical thermostats or electronic controls are possible for controlling the heating power.

The direct application of the temperature-resistant insulation layer to the metallic carrier and the use of electrical resistance pastes such as carbon conductive varnishes allow short-term power densities of up to 30 W / cm ² with sufficient energy dissipation.

With the method according to the invention, however, electrically insulating materials such as plastics, metal oxides and metal nitrites can also be printed. Due to the self-insulating property of the carrier material, there is no need to apply a basic insulation layer.

A carbon conductive lacquer preferred for the method according to the invention consists of coal dust and graphite with grain sizes between 5 and 7 μm. The solids content is preferably 67% and the specific weight 1.15. It is a one- or two-component, thermosetting resin mixture.

The surface heating element produced by the method according to the invention can be used for voltages up to 400V AC or 600V DC be used. However, the preferred area of application is 12 to 24 V DC or AC, and 230 to 400 V AC.

The particular advantages of the surface heating element according to the invention lie in the fact that geometrically shaped carrier materials of any shape can be used, which in turn can consist of any material. Thus, both electrically conductive carrier materials, for example made of aluminum, copper or steel, can be used, as well as those made of non-conductive material, such as plastic, metal oxide, metal nitrite, or also electrically conductive carriers, onto which an electrically insulating coating, for example, is made in a previous manufacturing step Enamel or glass was applied.

Another advantage is that there can be no detachment of the heat-generating electrical conductor and thus no overheating problems which affect the life of the heating element due to the formation of bubbles. Furthermore, due to the low process temperatures in the manufacturing process, no post-processing such as grinding or polishing is required.

If the electrical safety regulations regarding the contact voltage are adhered to, the outer insulating and covering layer can also be omitted under certain circumstances, without this endangering the durability of the electrically conductive layer.

From today's perspective, the main area of application is applications in the range up to about 100 ° C and low wing loads.

The invention is explained in more detail below by the embodiment variants shown in the figures. Show it:

Figure 1 shows a first embodiment of the invention in section.

2 shows a further embodiment variant of the invention in section;

3 shows a view of a further embodiment variant; and

Fig. 4 shows the variant of Fig. 3 in an axonometric view.

The surface heating element according to the invention is shown by way of example in the figures. However, it is expressly not limited to these embodiments. Therein Fig. 1 a carrier material 1, on which an insulating layer 2, two adjacent conductor tracks 3 and a covering insulating layer 4 are applied in successive process steps.

2 shows a carrier material 1, on which an insulating layer 2, two adjacent conductor tracks 3, a further insulating layer 5, a full-surface conductor 6 and a covering insulating layer 4 are applied in successive process steps.

3 shows a top view of a surface heating element according to the invention, the conductor tracks 3 covered by the insulating layer 4 being indicated by broken lines. Contact surfaces 7 are left free for the electrical connection when the insulating layer 4 is applied.

FIG. 4 shows the surface heating element from FIG. 3 in an oblique view, current connections 8 being recognizable on the contact surfaces 7.

Claims

PATENT CLAIMS

1. A method for producing a surface heating element as a resistance heater in a multilayer structure, which converts electrical energy supplied into heat energy and emits it to a carrier material and wherein the carrier material has a flat, curved or a multi-dimensionally shaped surface, characterized in that the heat-generating electrical conductor is applied to the substrate to be heated using a screen printing process and dried, the electrical conductor is then covered with an insulating layer on a plastic basis using a screen printing process or by spraying or rolling, and the insulating layer is dried and cured at temperatures of up to 300 ° C.

2. The method according to claim 1, characterized in that the carrier material consists of an electrically insulating material, such as plastic, metal oxide, metal nitrite or an electrically conductive carrier, on which in an earlier manufacturing step an electrically insulating coating, for example made of enamel or glass was applied.

3. The method according to claim 1, characterized in that the carrier material itself consists of an electrically conductive material, such as aluminum, copper or steel, and that before the application of the heat-generating electrical conductor, an insulating layer based on plastic is applied to the carrier material and at temperatures of maximum 300 ° C is dried and cured, and then the heat-generating electrical conductor is applied.

4. The method according to any one of claims 1 to 3, characterized in that a conductive paste made of a carbon conductive varnish is used as the heat-generating electrical conductor, which has a solids content of more than 60% and in addition to coal dust also graphite with a grain size of preferably 5 to 7 μm contains.

5. The method according to any one of claims 1 to 4, characterized in that a solder resist or an electrical insulation lacquer or an impregnating lacquer for electrical and / or electronic components is used as the insulating layer.

6. The method according to any one of claims 1 to 5, characterized in that the heat-generating electrical conductor is formed over the entire surface or is formed as a conductor track structure of any geometry.

7. The method according to any one of claims 1 to 6, characterized in that a plurality of layers of heat-generating electrical conductors are applied to the carrier material, which are separated from one another by insulating layers, with an insulating layer being followed by a drying step at temperatures of at most 300 ° C. after each application.

8. The method according to any one of claims 1 to 7, characterized in that the carbon conductive paint has a specific surface resistance of 1 to 1000 ohms / unit area.

9. The method according to any one of claims 1 to 8, characterized in that the electrically conductive paste is applied by screen printing with a thickness of about 10 to 50 microns.

10. The method according to any one of claims 1 to 9, characterized in that the insulating layer is applied by screen printing or by spraying or rolling with a thickness of about 20 to 200 microns according to the required test voltage.

11. The method according to any one of claims 1 to 10, characterized in that additional electrically conductive layers are applied with corresponding insulation layers, which are connected to the ground or a screen in order to comply with the necessary safety regulations, improve the equipotential bonding or influence the electromagnetic behavior ,

12. The method according to any one of claims 1 to 11, characterized in that the contact points provided for the electrical connection are kept clear when applying the insulating layer.

13. The method according to any one of claims 1 to 12, characterized in that the electrical connection is carried out by sticking tabs or other suitable metal electrodes with an electrically conductive adhesive or in a known manner by soldering or welding tabs or strands.

14. The method according to any one of claims 1 to 12, characterized in that the electrical connection is made by specially formed surface pressure contacts with an electrically highly conductive surface.

15. The method according to any one of claims 1 to 14, characterized in that the maximum specific surface load is 30 W / cm ² .

16. surface heating element as resistance heating in a multi-layer structure, which converts electrical energy supplied into thermal energy and emits it to a carrier material (1) which has a flat, curved or a multi-dimensionally shaped surface, and a heat-generating electrical conductor (3), characterized that the heat-generating electrical conductor (3) is applied to the carrier material (1) to be heated by means of a screen printing method and is covered with an insulating layer (4, 5) based on plastic, and that an insulating layer (2) between a metallic carrier and the heating element consists of a Solder resist or an electrical insulation varnish or impregnating varnish for electrical and / or electronic components, preferably in the thickness of 20 to 200 μm, and the resistance heater made of a carbon conductive varnish with a solid content of more than 60%, which in addition to carbon dust and graphite with a preferred grain size of 5-7 μm, a specific surface resistance of 1 - 1000 ohms / unit area and a thickness of 10 - 50 μm.

17. The method for using the surface heating element according to claim 16, characterized in that the surface heating element is used for voltages up to 400V AC or 600V DC, preferably for 12 to 24 V DC or AC, or for 230 to 400 V AC.