EP2457412B1 - Heater, in particular high-temperature heater, and method for the production thereof - Google Patents

Description

The invention relates to a method for producing a heater, in particular high-temperature heating, as well as such a heater, in particular a high-temperature heating, in which on a carrier material at a current flow heat generating layer is provided.

Such heaters, especially high-temperature heaters, are used for products of white goods, for example as a heater for an oven, toaster or hobs or glass ceramic hobs. To heat these objects up to temperatures of> 400 ° C so far heating rods are used, from which a heat radiation took place in order to heat the adjacent carrier material. The use of such heating elements leads to an inhomogeneous warm-up process. A targeted focus on the food or to be heated Good is not given. Furthermore, there is an air cushion between the heating wires and the carrier material, which has a negative effect on the heat transfer.

To avoid an inhomogeneous heating process, for example induction hobs are known in which the heat is generated directly in the cooking pot by eddy currents. As a result, although a homogeneous heating of the cooking material is achieved, however, the initial cost is complex, and it requires special pots for heating the food. However, this high-temperature heating can not be easily transferred to any white goods.

From the DE 10 2005 049 428 A1 is a plate-shaped heating element has become known, which is used for the air conditioning of homes and buildings. On a composite panel, a heating layer of a carbon-fiber mixture with non-conductive materials has become known, which is applied to a gypsum board or composite panel provided on the backside with a composite building material. For contacting the heating layer strip-shaped contact elements are provided, so that a surface heating of the layer is made possible on carbon-fiber mixture. Such sheet-like heaters allow due to their design of the heating layer only temperatures in a range of <50 ° C and are not suitable for the use of white goods. In addition, the application of such fiber blends or fiber fabrics is very costly.

The same applies, for example, for those from the DE 20 2005 013 822 have become known sheet-like heating elements, which are constructed analogously to the heating element for room air conditioning. Such composite systems with a paper-like fiber structure are complex to manufacture and costly. In addition, the adaptation to any geometry and easy application is difficult.

From the DE 100 01 330 A1 is an electric hotplate with at least one cooking zone has become known which uses glass ceramic, glass or ceramic as the carrier material. On the underside, an electrical insulation layer is provided for heating the cooking zones and a thermally insulating cover layer, wherein a Heizwiderstandsmaterial is provided therebetween lying. The heating resistor material consists of electrically conductive carbon, graphite particles or carbon fibers which are contacted with electrodes. The heating resistor element may be mixed with a binder of heat-resistant organic or inorganic substances. The second thermally insulating covering layer applied thereon terminates airtight with respect to the atmosphere of the heating resistance element, wherein the covering layer consists of heat-resistant glass or an enamel layer. The assembly of the hot plate body is carried out by electrochemical bonding of the superimposed layers, wherein it is provided that the heating resistance element is brought by heating to a temperature above 400 ° C and in addition an electrical voltage of more than 400 V to the hotplate body and the Heizwiderstandselement is applied.

This layer structure of the cooking zone has the disadvantage that a complex representation of the adhesion properties is given by high voltages and no free choice of the contacting method is possible because the contact must be directly on the conductive layer.

From the DE 103 36 920 A1 Furthermore, an electric roasting oven plate for heating, which is based on a structure of the electric hotplate according to of the DE 100 01 330 A1 Reference, this structure for electric baking, cooking or electric roasting ovens should be used.

From the DE 20 2009 000 136 U1 An infrared CNT heating device is known, which comprises a thermally loadable molded body with an electrically conductive structural layer, which generates infrared heat rays when current flows through. The electrically conductive structural layer consists of CNT materials, which are obtained by extraction or manual application of CNT suspensions and applied to the molding with suitable support materials such as gel or pasty emulsions. A functional coating of thermally treated ceramic, metal, enamel, blocking, adhesive or insulating layer may be present between the shaped body and the conductive structural layer.

The invention has the object of providing a method for producing a heater, in particular a high-temperature heating and a heater, in particular a high-temperature heating to propose, in which a heating element in a simple manner can be applied over the entire surface as a thin layer and allows homogeneous heat transfer.

This object is achieved by a method for producing a heater, in particular for thermal household appliances, in which on the carrier material, a first electrically conductive layer is applied, which is formed from a flowable base material and carbon nanotubes dispersed therein that on the first Layer, a protective layer is applied, which penetrates by applying to the first layer in this, by compressing the layers by a temperature treatment and to prepare the protective layer, a silicate is used to form an inorganic layer.

This method makes it possible to produce a very thin heating element which can be heated up very quickly and allows a uniform heat transfer to the carrier material. The heat treatment process after applying the first layer and the protective layer has surprisingly revealed that the carbon nanotube selected as the conductive material is temperature resistant in the first layer and the protective layer can be introduced and burning is avoided. By using a silicate as a protective layer, the carbon nanotubes dispersed in the base material can be completely incorporated or protected from the environment, so that especially at elevated temperatures oxidation protection of the carbon nanotubes is given, since they begin to degrade at these high temperatures , By penetrating the protective layer and the subsequent compression of this degradation is counteracted. As a result, a heating element is provided which enables a corresponding thermal shock stability and a mechanical adhesion to the carrier material. By the heat treatment or by heating, in addition to the first layer and the protective layer, a compression of the layers is achieved. This has the advantage that such Hochtemperaturheizelemente be compressed air or oxygen tight. As a result, the temperature stability of the dispersed carbon nanotubes can be achieved.

According to a preferred embodiment of the method, it is provided that the at least one layer is contacted with contact elements and the layers applied to the carrier material are heated. As a result, an increased mechanical adhesion between the contact element and the carrier material can be achieved.

A further preferred embodiment of the method provides that the contact elements are strip-shaped. As a result, a sheet-like heating can be achieved.

According to a preferred embodiment of the method is provided that the applied first layer and protective layer is heated in particular to a temperature between 300 ° C to 700 ° C. By this temperature treatment, a sintering process of the layers takes place. This can be done in particular a compression of the layers. This has the advantage that such high-temperature heaters are compressed by the sintering oxygen-tight and thus suitable for operation at temperatures of> 400 ° C and are resistant.

A preferred embodiment of the method provides that the first layer is dried after application and then the protective layer is applied. This drying process has the advantage that the first layer is at least slightly compressed, in particular water-soluble constituents can evaporate before the further protective layer is applied. As a result, a thin structure of the heating element can be favored.

According to a further preferred embodiment of the method, it is provided that the first layer and separately the protective layer or the functional layer are applied by a spray method by knife coating or a printing process. For example, a screen printing method can be provided, by which the in particular pasty first layer is applied in a simple manner to the carrier material. Subsequently, the likewise preferred pasty trained second protective layer can be applied in the same way. Thus, known technologies can be used for the production of high-temperature heating elements. Alternatively, a spraying method or a spraying method may be provided in order to apply the first and second layer to the carrier material. Here, a so-called spray coating, a dip coating, so a dip coating or a spin coating can be realized.

A further preferred embodiment of the method provides that the first layer is applied over the entire surface or in adjacent strips, the protective layer is applied over the entire surface of the first layer and this completely envelopes the substrate, in particular before or after the application of the first layer strip-shaped contact elements be applied. Thereby, the first layer is connected as an electrically conductive layer with the strip-shaped contact elements and then allows electrical insulation through the protective layer with the exception of connection points on the strip-shaped contact elements. The complete encapsulation of the first electrically conductive layer by the protective layer further makes it possible to use water-soluble materials as the basis for a dispersion for the production of the first electrically conductive layer. These in turn have the advantage that processing without the use of solvents is possible and thus harmless to health.

A further preferred embodiment of the method provides that before applying the first layer to the carrier material in the heating region, an electrically insulating layer is applied to the carrier material. This is done in particular when the carrier material is not made of a dielectric material, but of an electrically conductive or weakly electrically conductive material.

A preferred embodiment of the method provides that an aqueous solution, in particular water or distilled water, is used for producing the first layer as electrically non-conductive base material, which preferably comprises a dispersant, such as gum arabic. This allows easy application, in particular as a full-surface layer, without using solvents for the preparation of the dispersion as well as for the cleaning of machines.

A further preferred embodiment of the method provides that incorporated into the electrically non-conductive base material fillers of carbon nanotubes and / or graphite and this paste can then be printed. The last step describes the application of the protective layer (TopCoat), which preferably consists of ethyl silicate with graphite.

In this case, single, double or multiwalled nanotubes can preferably be used. In particular, the combination of graphite and carbon nanotubes has the advantage that a flowable dispersion for the first layer for full-surface application to a carrier material is achieved.

• 1) Haftung durch Penetration; 2) Isolierung gegen Luftsauerstoff; 3) leitfähige, CNT freie Schicht zur Durchkontaktierung.

According to a further preferred embodiment of the method, it is provided that a filler, in particular graphite, is dispersed in the protective layer. This has the advantage that, in particular in the first alternative embodiment of the method when penetrating the protective layer into the first electrically conductive layer, the filler ratio is increased, as a result of which the conductivity in the second layer also increases. As a result, the contacting can be applied at any desired time and flexibly attached to different locations. The protective layer is not only used for insulation against atmospheric oxygen, By the addition of graphite, which is more stable in air temperature than the CNTs, a functional layer for effective via contact is also given after the penetration and the resulting shift of the weight percentages of the fillers. Overall, this layer has three characteristics:

• 1) liability by penetration; 2) insulation against atmospheric oxygen; 3) conductive, CNT-free layer for via.

Furthermore, it is preferably provided that an adhesive, in particular gum arabic, is dispersed into the first layer. As a result, an adhesion mediation between the first layer and a carrier material can be improved. The gum arabic is used before the application of the protective layer (TopCoat) as a primer. This guarantees that when printing the protective layer (TopCoat) this does not destroy the first layer (PreCoat).

During the penetration of the layers, the gum arabic is burned out. Before the protective layer forms gas-tight, the volatile constituents of gum arabic diffuse out. As an alternative to gum arabic, other surfactants such as SDS or Triton are also conceivable.

The object is further achieved according to the invention by a heating element, in particular a high-temperature heating element, for example for thermal household appliances, in which a first electrically conductive layer consisting of a base material and a carbon nanotube dispersed therein and a protective layer are provided on the carrier material the first layer is penetrated and that the protective layer consists of silicate. This special design of the heating element allows high temperature resistance and thermal shock stability to be achieved. At the same time, any desired geometries for the heating elements on a carrier material, in particular for forming a high-temperature heating, can thereby be selected.

A preferred embodiment of the heating element provides that the layers are contacted with contact elements. As a result, a simple connection can be created.

Preferably, the contact elements are strip-shaped.

Eint further preferred embodiment of the heating provides that the layers are compressed by a temperature treatment. As a result, the temperature resistance and / or thermal shock stability can be further increased.

Furthermore, it is preferably provided that the first layer and the protective layer form a heating element with a layer thickness of less than 500 μm, in particular less than 100 μm. Due to the choice of materials, an ultra-thin application may be possible. At the same time, a homogeneous heat generation within the first electrically conductive layer and thus of the carrier material can take place.

The heater preferably has a first layer, which has a concentration of 0.1 to 100 wt% CNT in the flowable base material, in particular in water or distilled water. This can be given a high electrical conductivity, so that you can work with low voltages. Preferably, a concentration of 1 to 3 wt% CNT and 5 to 50 wt% graphite is provided as a filler in the base material. By adding graphite, the flowability of the first layer or the mixture can be increased.

The heating element preferably has a heating element with a first layer and a protective layer which has an electrical resistance of less than 100 ohms / sq. having. This allows a temperature generation of> 400 ° C on large substrates by means of a conventional power supply in the home. In addition, the layers could be made even thinner to ensure even better mechanical stabilities.

To produce the heating, a carrier material is preferably provided which consists of ceramic, glass ceramic, ceran ceramic, aluminum oxide ceramic, MgO, KER 520. As a result, a variety of applications, especially in the white goods, allows. At the same time, a cost-effective production can be achieved.

Figur 1

eine schematische Schnittdarstellung einer ersten Ausführungsform einer Heizung,

Figur 2

eine schematische Seitenansicht von unten auf die Heizung gemäß Figur 1,

Figur 3

eine schematische Seitenansicht einer alternativen Heizung zu Figur 1 und

Figur 4

eine schematische Seitenansicht einer weiteren alternativen Ausführungsform zu Figur 1.

The invention as well as further advantageous embodiments and developments thereof are described below with reference to the drawings illustrated examples described and explained. The features to be taken from the description and the drawings can be applied individually according to the invention individually or in combination in any combination. Show it:

FIG. 1

a schematic sectional view of a first embodiment of a heater,

FIG. 2

a schematic side view of the bottom of the heater according to FIG. 1 .

FIG. 3

a schematic side view of an alternative heating to FIG. 1 and

FIG. 4

a schematic side view of another alternative embodiment to FIG. 1 ,

In FIG. 1 is a schematic side view of a heater 11, in particular a high-temperature heating shown. FIG. 2 shows a schematic view from below. The high-temperature heating 11 comprises a carrier material 12, which may be formed, for example, when used in the field of white goods as ceramics, glass ceramic, Cerankeramik, alumina ceramics or the like. On the underside of a heating element 14 is provided within a heating area. This heating element 14 comprises a first electrically conductive layer 16, on which a protective layer 17 is applied. Preferably, the protective layer 17 completely surrounds the first electrical layer 16, so that it is electrically insulated and mechanically protected against the environment on the substrate 12 is provided. The first electrically conductive layer 16 extends between two strip-shaped contact elements 18, which are guided for contacting the electrical layer 16, for example, to an edge region of the carrier material 12. Between the two preferably parallel to each other extending contact elements 18, the first layer 16 extends and forms the heating area. The protective layer 17 covers the first layer 16 and preferably the strip-shaped contact elements 18, so that only for example in the edge region a free contact point can be recessed. Alternatively, it can also be provided that initially the first layer 16 and the protective layer 17 are applied and then the strip-shaped contact elements 18 are brought to the heating zone formed by the first layer 16 and protective layer 17.

The first electrically conductive layer 16 consists of a flowable, electrically non-conductive base material. Preferably, an aqueous-based dispersion is provided. Carbon nanotubes are dispersed in this dispersion as an electrically conductive material. In addition, the dispersion comprises a filler, in particular graphite, in order to support the electrical conductivity and to adjust the flowability. In addition, an adhesive is preferably provided in the dispersion. This may be, for example, gum arabic. Other surfactants such as SDS or Triton can be used. As a result, a flowable or pasty mass can be produced, which can be applied to the carrier material 12 by a printing process or spraying process. This dispersion is high-temperature, thermoshock-stable and hydrophobic. The protective layer 17 is preferably made of a silicate, which may preferably be enriched with adhesive, filler or other particles in order to increase the adhesion properties. As a result, the thermal shock stability and the mechanical adhesion to the substrate can be improved. By penetrating the protective layer 17 into the first layer 16, these CNTs are also suitable for use at temperatures above 350 ° C., since the protective layer 17 encloses the CNTs airtight. The electrically conductive material preferably consists of a composite of CNTs and graphite or further electrically conductive particles or constituents which make it possible to form a pasty mass or a sprayable mass.

This in FIG. 1 shown heating element 14 is prepared by first mixing the components of an electrically non-conductive base material and carbon nanotubes dispersed therein or a composite of carbon nanotubes with other electrically conductive materials to form a flowable or pasty mass, which by means of a Screen printing process is applied over the entire surface of the substrate 12. Subsequently, the strip-shaped contact elements 18 can preferably be printed by applying a conductive paste, in particular silver conductive paste, by screen printing. These contact elements 18 can also be provided on the carrier material 12 before the application of the first layer 16. Following this For example, according to a variant of the first embodiment of the production method, this first layer 16 can be subjected to temperature treatment. This has the advantage that hardening and drying of the base material or the aqueous base takes place for the first layer 16 formed as a dispersion, whereby a subsequent penetration of the protective layer 17 is improved. Subsequently, the protective layer 17 is preferably applied by a screen printing method. Alternatively, this can also be applied without an intervening drying process of the first layer 16. Subsequently, the carrier material 12 is treated with the layers 17 applied thereto as well as the contact elements 18, so that at least the protective layer 17 is preferably sintered. Here the compression takes place and requires a further "compression" of the conductive particles, which due to the increased number of contacts and the compactness to a lower spec. Resistance leads. This in turn can be used to create a conductivity improvement in the first layer 16.

Such high-temperature heaters 11 have heating elements 14, the thickness of which may be formed, for example, <100 μm. In addition, due to the full-surface arrangement of the electrically conductive layer 16 on the carrier material 12, a homogeneous heating and thermal radiation of the carrier material 12 is made possible.

Preferably, the protective layer 17 may be associated with a reflector to reflect the heat radiation from the heating element 14 in the opposite direction to the carrier material 12 and to accelerate the heating of the carrier material 12.

In FIG. 3 is an alternative embodiment to FIG. 1 shown. This embodiment differs from that in FIG FIG. 1 from that prior to the application of the first electrically conductive layer 16, an electrical insulating layer 19 is applied over the entire surface of the carrier material 12 in order to arrange the electrically conductive layer 16 relative to the carrier material 12 in isolation. This arrangement of the insulating layer 19 may also be provided when applying a mixture consisting of the first electrically conductive layer 16 and the protective layer 17. Likewise, before applying the functional layer 21 on the substrate an electrically insulating layer 19 are applied over the entire surface.

In FIG. 4 is an alternative embodiment to FIG. 1 shown. This embodiment differs only in that instead of a full-surface first electrically conductive layer 16, a strip-shaped layer 16 is formed. Such webs or ribs can be adapted in geometry and contour to the corresponding applications. The strip geometry can heat targeted areas. In addition, it further favors the adhesion properties of the respective substrate. The strips can be arranged as desired, so that different heating zones can be implemented on a substrate in a targeted manner.

Claims (17)

1. Method for producing a heating installation, particularly for thermal household appliances, in which a layer generating heat by electricity flow is provided on a substrate (12) as a heating element (14), and on the substrate (12), a first electrically conductive layer (16) is applied, which is formed from a flowable base material, and carbon nanotubes dispersed therein, characterised in

   - that on this first layer (16), a protective layer (17) is applied, which by means of the application onto the first layer (16) penetrates into this,

   - that the layers (16, 17) are compressed by temperature-treatment and

   - that for producing the protective layer (17), a silicate is used to form an inorganic layer.
2. Method according to claim 1, characterised in that the at least one layer (16, 17) contacts with preferably strip-shaped contact elements (18), and the layers (16, 17), applied to the substrate, are heated, in particular are only heated by applying a voltage to the contact elements (18).
3. Method according to any one of the preceding claims, characterised in that the layers (16, 17), applied on the substrate (12), are heated to a temperature of 300 °C to 700 °C.
4. Method according to claim 1, characterised in that the first electrically conductive layer (16) is dried after application on the substrate (12), and the protective layer (17) is subsequently applied.
5. Method according to any one of the preceding claims, characterised in that the first electrically conductive layer (16), and, separately, the protective layer (17) are applied by a spraying process, by squeegee or a printing process.
6. Method according to any one of the preceding claims, characterised in that the first electrically conductive layer (16) is applied onto the substrate (12) over the whole area or in strips, whereby the protective layer (17) is subsequently applied onto the first layer (16) over the whole area, and covering the substrate (12), whereby before or after the application of the first electrically conductive layer (16) or protective layer (17), strip-shaped contact elements (18) are applied on the substrate (12).
7. Method according to any one of the preceding claims, characterised in that before the application of the first electrically conductive layer (16) in the heating region, an electrically insulating layer (19) is applied onto the substrate (12).
8. Method according to any one of the preceding claims, characterised in that for producing a first electrically conductive layer (16), as a non- electrically conductive, flowable base material, an aqueous solution, particularly water or distilled water is used, which preferably includes a dispergent, such as gum arabic, for example.
9. Method according to any one of the preceding claims, characterised in that carbon nanotubes and/or graphite are dispersed as an electrically conductive, flowable material into the base material, of the first electrically conductive layer (16).
10. Method according to claim 1, characterised in that a filler, particularly graphite, is dispersed into the protective layer (17).
11. Method according to claim 1, characterised in that an adhesive agent, particularly gum arabic, is dispersed into the first layer (16).
12. Heating installation, particularly high-temperature heating installation, in particular for household appliances, which comprise a layer generating heat by electricity flow on a substrate (12) as a heating element (11), characterised in that on the substrate (12), a first electrically conductive layer (16) consisting of a base material and carbon nanotubes dispersed therein and a protective layer (17) is provided, which is penetrated into the first layer (16), and that the protective layer (17) consists of silicate.
13. Heating installation according to claim 12, characterised in that the layers (16, 17) are contacted with particularly strip-shaped contact elements (18).
14. Heating installation according to claim 12 or 13, characterised in that the first and second layer (16, 17) comprise a layer thickness of less than 500 µm, particularly less than 100 µm.
15. Heating installation according to claim 12 to 14, characterised in that the first electrically conductive layer (16) has a concentration of 0.1 to 100 wt% carbon nanotubes in the flowable base material, or that a matrix of a concentration of 1 to 3 wt% carbon nanotubes and 5 to 50 wt% graphite is provided in the base material.
16. Heating installation according to claim 12 to 15, characterised in that the heating element (14) produced by the first and second layer (16, 17) has an electrical resistance of less than 100 Ω/Sq.
17. Heating installation according to claim 12 to 16, characterised in that the substrate (12) consists of ceramic, glass ceramic, Ceran ceramic, aluminium oxide ceramic, MgO, KER500.

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