EP0157179B1 - Flat ceramic support with an electric resistance layer and method for adjusting the resistance value of the resistance layer - Google Patents

Description

The invention relates to a flat ceramic molded body according to the preamble of claim 1.

The elements used for space heating are in the form of finned radiators or surface radiators, generally located below window openings, so that the room air heated by them rises above the window openings and thus generates a warm air curtain in front of the window opening. Even when radiators are installed on walls, there is an air movement from the floor to the ceiling of the room heated with them, the heat radiated into the room by the radiator only playing a minor role.

Standard pure radiant heaters installed in rooms only have a locally very limited radiation area and work at high temperatures.

The prior art also includes underfloor heating systems in which heating coils acted upon by liquid heat transfer medium, but also electrical heating conductors, are accommodated in the screed or below the top floor covering. Underfloor heating systems are comparatively cumbersome and expensive to build and require comparatively complex controls.

There is therefore a need to design design elements of the space boundary itself so that they can take over the task of heating the space or a part of the space boundary to be heated or kept warm individually, in groups or as the entire space boundary or a substantial part thereof.

Examples of such design elements of room boundaries are ceramic moldings such as plates, which serve as floor or wall cladding plates for the design of the walls or the floor or the ceiling of living, business and office spaces, but also of sanitary rooms, sports and swimming pools serve. Such ceramic moldings can also be shaped stones for swimming pool linings and the like. be.

A brochure, published by Canespa KG, 3005 Hemmingen-Westerfeld, Gutenbergstrasse 13, in 1975, already shows a "Canespa-Therm" wireless heating system in which molded bodies, namely ceramic plates, a heating lacquer layer as an electrical resistance coating. is applied.

This heating lacquer layer is covered by a polyurethane foam body. However, this system could not prevail because local overheating occurred repeatedly with the resulting harmful extensions, which even put people and property at risk.

According to DE-A 14 40 971, the state of the art also includes an electric space heater which has a support with a large smooth surface and a flat, thin heating conductor which adheres directly to the surface. The carrier consists of an earthenware or quartz plate. This plate is provided on its side facing away from the visible side with a firmly adhering thin areal metallic heating conductor coating formed by precipitation from a chemical solution or carries on this side a firmly adhering heating conductor coating consisting of a very thin aluminum layer.

In such a space heater, it is necessary to provide spacers between the plate and the support surface receiving it, which in turn creates a draft channel for the room air behind the space heater with all the disadvantages already noted in other space heaters and described above. In addition, the metallic resistance layers used have a comparatively low resistance value and require high electrical power in order to achieve a sufficient heat yield.

From DE-A 19 24 202 and the unpublished DE-A 33 25 204 a sheet-like electrical heating device is known with a flat support receiving a heating element, in which the heating element is in the form of a thin layer of electrically conductive material on a Surface of the carrier is applied. Even if, as described in DE-A 33 25 204, the electrically conductive material consists entirely or partially of semiconductor material, no success can be achieved because the layers of such material cannot be reproducibly produced with respect to their electrical resistance. The heaters therefore have different heating powers from piece to piece.

In a known heating element (DE-A 25 35 622), a heating conductor layer, which is covered on the outside by a protective plastic layer and which is formed from graphite particles dispersed in a solvent, is provided on a carrier layer made of ceramic material. Since the carbon dispersion shows a negative temperature dependence, compensation particles made of metal or metal oxide are built into the heating conductor layer, which have a positive temperature dependence. This compensation is intended to achieve a uniform specific resistance of the heating conductor layer. Uniform heating conditions cannot, however, be achieved if, as a result of the roughness inherent in a ceramic shaped body, varying layer thicknesses result over the surface of the ceramic shaped body.

Finally, heating elements are also known (FR-A 2 211 832), in which a resistance coating with metallic particles embedded therein is applied to the visible side of a ceramic carrier. In another known heating element (FR-A-2 490 056), on the visible side of a carrier layer made of ceramic material, a resistance coating is applied, which is formed from several zones with different conductive particles.

The object of the invention is to provide a space heating element which not only delivers a high heat yield with low electrical power consumption, can be used as a design space limitation element and can be installed in this way, that it does not lead to the formation of channels, are forced through the room, but is also reproducible as desired, ie has the desired heating output from piece to piece.

This object is achieved by a space heating element with the features of claim 1. The present patent claims only the excess relating to the areal extent and the ratio of thickness to areal area compared to the patent corresponding to application number 85 102 230.

The non-metallic, large specific surface area, electrically conductive particles which do not significantly change their electrical conductivity when the temperature increases are preferably those made of graphite and carbon black or mixtures thereof.

With the proposal according to the invention, it is possible to create a space heating element in the form of a radiant heating element, with which one can cover, for example, an entire wall, ceiling or floor area with uniform heat radiation or heat radiation in the desired arrangement by any multiplication. There is no recirculation of the room air, and the same feeling of wellbeing can be achieved in the room with a significantly lower room temperature, which leads to considerable energy savings.

If, for example, an area of 120 x 120 cm is to be covered with panels, then a coverage of 30 x 30 cm panels, as was previously the case, results in a loss area of approx. 19.8%, calculated on the total area is not available for the radiation. This loss area is reduced to 8.8% when using the proposal according to the invention when using plates of the specified type in the size of 60 x 60 cm. These values can be improved even further if the surface dimensions of the plates are increased further.

There are plates manufactured by the applicant with dimensions of up to 200 x 200 cm, which can be provided with appropriate resistance coatings and also allow any decoration to be designed by means of division and in combination with plates of smaller dimensions. Overheating, in particular local overheating, has not been observed; rather, large plates of this type are distinguished by an extraordinarily good radiant power.

Furthermore, uniform surface heating can be achieved since the moldings are exactly reproducible with regard to their heating output.

In the event of local faults in the electrical resistance coating, the heating output is practically not interrupted. At most, there is a slight local reduction in the heating output, but not a complete interruption of the same. In addition, there is no local overheating.

The electrical resistance coating can consist of a layer of an aging-resistant synthetic resin with an electrically conductive admixture e.g. a pure graphite admixture and of such a structure that the layer has a resistance value which is necessary in accordance with the required electrical power.

The resistance value can be set to values from a few 0 to several k0 by changing the proportion of conductive, e.g. Graphite admixture and / or change in layer thickness. The layer thickness is usually between 10 and 50 Ilm.

With a 100 cm x 100 cm plate, the electrical power consumption is, for example, approximately 100 W, with a 60 x 60 cm plate, approximately 30 W.

In the case of the layer selected in accordance with the invention, aging-resistant means resistance to continuous stress up to approximately 100 ° C. over the life of the ceramic molded body.

In an alternative embodiment of the invention, the electrical resistance coating consists of an electrical resistance film which has a polyester cover layer, an electrically conductive intermediate layer provided with supply and discharge lines, e.g. has a graphite and / or carbon black layer as a resistance layer and a polyester underlayer. Such resistance foils are known per se. The supply and discharge lines to the resistance layer are generally in the form of copper strips. However, the problem of using such resistance foils is that polyester layers adhere poorly to the resistance layer, so that a ceramic molded body provided with such a resistance foil on the side facing away from the visible side can also be used when using e.g. on a plastered wall or the back of the molded body and adhesive adhering to the polyester layers, a hold of the molded body, e.g. a ceramic plate at the place of attachment is not guaranteed with sufficient certainty. On the other hand, the use of polyester as a material for the top and bottom layers is recommended because polyester is very resistant to aging. The problem that arises when using polyester material for the top and bottom layers of the resistance film can be solved, however, if, according to a modified embodiment of the invention, the resistance layer is divided into areas, leaving areas not covered by it, the link surfaces are electrically connected to one another and in the areas not covered by the resistance layer are provided with local openings in the resistance foil.

You can work with an adhesive that only adheres to plaster and ceramic surfaces, but not or only poorly to a polyester surface, because the resistance film breaks through locally, e.g. punched through and applied to the side of the ceramic body facing away from the visible side of the ceramic body via the adhesive exposed in the openings or at least partially penetrating them.

If a shaped ceramic body formed in this way is glued to a plaster layer or the like with the aid of an adhesive which is customary for adhering shaped ceramic bodies to wall surfaces or the like, then liability is given by the exposed or emerging from the openings the adhesive, and so one obtains a fixing of the ceramic molded body to the substrate provided for its reception, which is only local, but is sufficient if the opening grid is dimensioned correctly.

It is particularly advantageous to apply the electrical resistance coating in the form of a resistance glaze. This glaze is applied to the already fired shaped body and fixed by firing the shaped body again. A glaze whose melting point does not exceed 750 ° C. must be selected as the glaze. Glazes with a higher melting point have proven unsuitable.

Another possibility is to design the adhesive with which the ceramic molded body is to be fixed on the substrate as an electrical resistance. It is possible to use two different types of adhesive, the adhesive adjacent to the molded body being made of electrical resistance material, while the adhesive to be placed on the substrate is an electrically insulating adhesive. The adhesives have essentially the same thermal expansion properties and chemical compatibility, so that a particularly simple fastening of the ceramic electrical resistance molded body is possible in this way.

It is already known from DE-A 19 24 202 to apply an electrically conductive glaze on the visible side of ceramic shaped bodies. However, this glaze only serves to discharge static electricity, i.e. it is so high-impedance that it is unsuitable for heating purposes.

A material can be selected as the material for the electrically conductive resistance layer which, when exposed to electrical current, has a temperature response such that the current consumption of the material decreases sharply with increasing heating.

In DE-A 33 25 204, when using semiconductors as the conductive material for a heating element, it is stated that semiconductors in particular would have a desired negative temperature coefficient, but this is contradicted by the statements in Römpp, according to which the conductivity in semiconductors is normally strong with Temperature increases.

The electrical resistance coating is expediently contacted by contacting elements which are arranged symmetrically on the electrical resistance layer. For example, in the case of square or rectangular plates, the contacting elements can be provided in the form of contacting strips along two edges of the plate that face away from one another.

If the plate is a ceramic plate that has a relief on its back, the contacting elements are expediently placed in the channels on the edges facing away from one another between the webs delimiting them.

A further development of the invention makes it possible to subsequently fine-tune the resistance values of electrical resistance coatings on such shaped bodies to desired values.

According to the development of the invention, this is done by reducing the layer thickness of the resistance coating or heating the resistance coating to increase the resistance value.

When increasing the resistance value of the resistance coating, it is expedient to proceed in such a way that the layer cover of the resistance coating is reduced by sandblasting, electroerosion, brushing or the like, or the resistance layer is heated from the outside, for example by flaming or irradiation. However, it is also possible to conduct electrical current through the resistance coating with a considerably higher strength than during normal operation. This changes the structure of the resistance coating so that there is a corresponding increase in the overall resistance value.

• Fig. 1 eine Rückansicht eines als Platte ausgebildeten Formkörpers mit elektrischer Widerstandsschicht und Kontaktierungselementen;
• Fig. 2 eine Draufsicht auf eine keramische Platte, auf die eine elektrische Widerstandsfolie aufgebracht ist;
• Fig. 3 einen stark vergrößerten Teilschnitt durch die Platte nach Fig. 2; und in
• Fig. 4 einen Schnitt durch eine mit Widerstandbeschichtung versehene Platte.

The drawing shows in

• Figure 1 is a rear view of a shaped body formed as a plate with an electrical resistance layer and contacting elements.
• 2 shows a plan view of a ceramic plate to which an electrical resistance film is applied;
• 3 shows a greatly enlarged partial section through the plate according to FIG. 2; and in
• Fig. 4 shows a section through a plate provided with a resistance coating.

In Fig. 1, 1 generally designates a ceramic plate, the dimensions of which are e.g. 85 x 125 cm with a thickness of 0.8 cm. On the back 2 there is an electrical resistance layer. 3 and 4 denote band-like contacting elements which are glued to the electrical resistance layer or fastened to it in another way. 5 and 6 mean the power supply lines.

In FIG. 2, 31 generally designates a ceramic molded body which, as shown in FIG. 3, is made up of a ceramic plate 41, an adhesive layer 42 and a resistance film 43. The resistance film consists of a polyester cover layer 46 connected via the adhesive layer 42 to the side 45 facing away from the visible side 44 of the plate, one at the edge with supply and discharge lines in the form of copper strips 32, 33 with power supply lines 32 ', 33' (Fig. 2) provided graphite and / or carbon black intermediate layer 47 as a resistance layer and a polyester lower layer 48, via which the ceramic molded body to the supporting surface 50, for example a plastered wall is glued on. In the exemplary embodiment shown, the resistance foil 43 contains three tracks 43a, 43b, 43c with resistance layer material.

Areas 51 and 52, in which no resistive layer material is present, are located between the tracks 43a and 43b or 43b and 43c. In contrast, the web 43a borders on the region 51 via a conduction band similar to the conduction band 32 or 33. Likewise, the web 43 via a corresponding conduction band on the region 52, while the web 43b borders on the regions on both sides via conduction lines 51 and 52 adjacent. In the areas 51 and 52, in which the layers 46 and 48 lie one on top of the other, there are openings 53 through which the adhesive 42 extends and is connected to the adhesive 54 on the supporting surface 50. The individual conduits can be interconnected in any way. Instead of a single plate 31, three partial plates respectively assigned to the webs 43a, 43b and 43c can also occur.

In the case of the possible configuration of the conductive intermediate layer or resistance layer in an embodiment in which it is divided in terms of area while leaving areas not covered by it, it can e.g. are a meandering arrangement of the resistance layer or a subdivision of the same into several flat, but electrically connected or subsequently to be connected sub-layers in the form of strips, flat pieces or the like. The selection of the appropriate pattern depends on the local conditions and / or the technical requirements.

4, a ceramic plate is indicated at 91, on which a resistance layer 92 is applied. The application thickness of this resistance coating 92 is determined by means of a suitable measure, e.g. Sandblasting, electroerosion, brushing or the like reduced in thickness, in the illustrated embodiment with the aid of e.g. rotating brush 93, so that the application thickness decreases to the desired thickness, as indicated in the area 94.

This also reduces the conductivity of this layer, i.e. the surface resistance increases.

Claims (8)

1. A flat ceramic shaped body provided on one side with an electrically resistive coating exhibiting nonmetallic, electrically conductive particles having a large specific surface and not substantially altering their electric conductivity at higher temperatures, in particular graphite, characterized in that a tile is used that is pressed from a plastic ceramic starting material, rolled and baked and whose thickness is at least 1:45 000 relative to the surface area and whose surface area is at least 3600 square centimeters, the electrically resistive coating is disposed on the side of the ceramic body facing away from the visible side, and the particles are embedded in an electrically nonconductive or poorly conductive carrier substance in such a way that the resistive coating has an even electric and thermal conductivity.

2. The shaped body of claim 1, characterized in that the electrically resistive layer consists of an electrically resistive film which is fixed at least locally, preferably glued across the surface, to the side of the ceramic shaped body facing away from the visible side, and consists of a polyester cover layer, a conductive intermediate layer as a resistive layer provided with supply lines and removal lines, and a polyester bottom layer, and in that the resistive film is attached to the side of the ceramic shaped body facing away from the visible side with an adhesive that adheres both to a ceramic surface and to a polyester surface.

3. The shaped body of claim 2, characterized in that the resistive layer is divided up across its surface leaving areas not covered thereby within the resistive film, the divided areas communicating electrically with each other and local perforations being provided in the resistive film in the areas not covered by the resistive layer.

4. The shaped body of claim 1, characterized in that the electrically resistive coating consists of an electrically resistive glaze whose melting point is not higher than 750 degrees Centigrade.

5. The shaped body of claim 1, characterized in that the electrically resistive coating consists of an electrically resistive adhesive.

6. The shaped body of claim 5, characterized in that the electrically resistive adhesive is covered by an electrically insulating adhesive.

7. The shaped body of any of the above claims, characterized in that the electrically resistive layer is provided with conductive contacting elements, and in that the conductive contacting elements are made substantially of the basic material of the resistive layer in which particles of high electric conductivity or the existing conductive particles in a higher concentration are embedded additionally to increase the electric conductivity.

8. The shaped body of any of claims 1 to 7, characterized in that the distribution of the conductive particles is locally denser in the resistive layer.

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