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

Abstract

A heater, in particular a high-temperature heater, for example for domestic heating appliances, in which a layer that produces heat when a current flows through is provided on a carrier material as a heating element, wherein a first electrically conductive layer which is formed from a free-flowing, non-electrically conductive base material and carbon nano tubes dispersed therein is applied to the carrier material, wherein a protective layer is applied to this first layer and at least partly penetrates into the first layer as it is applied, or wherein a functional layer with carbon nano tubes dispersed therein is applied to the carrier material, and wherein the at least one layer or the functional layer makes contact with strip-like contact elements, and the layers applied to the carrier material or the functional layer are heated.

Claims

1. A heating installation comprising: a substrate; a first electrically conductive layer on the substrate, the first electrically conductive layer including base material and carbon nanotubes dispersed in the base material; and a protective layer provided on the first electrically conductive layer; wherein the protective layer is penetrated into the first electrically conductive layer through a surface of the first electrically conductive layer.

2. The heating installation according to claim 1, wherein at least the first electrically conductive layer is contacted with strip-shaped contact elements.

3. The heating installation according to claim 1, wherein the first electrically conductive layer and the protective layer have a combined layer thickness of less than 500 m.

4. The heating installation according to claim 1, wherein the first electrically conductive layer has a concentration of 0.1 to 3 wt % carbon nanotubes in the base material.

5. The heating installation according to claim 1, wherein the first electrically conductive layer has a concentration of 1 to 3 wt % carbon nanotubes in the base material, and a concentration of 5 to 50 wt % graphite in the base material.

6. The heating installation according to claim 1, wherein the heating installation provided by the first electrically conductive layer and the protective layer has an electrical resistance of less than 100 /Sq.

7. The heating installation according to claim 1, wherein the substrate is selected from the group consisting of: ceramic, glass ceramic, aluminium oxide ceramic, and MgO.

Description

(1) The invention as well as advantageous embodiments and further developments of the same are subsequently explained in more detail and described by means of the examples shown in the drawings. The features to be taken from the description and the drawings can be used individually or in any combination according to the invention. In the drawings:

(2) FIG. 1 is a schematic sectional representation of a first embodiment of a heating installation,

(3) FIG. 2 is a schematic side view from below of the heating installation according to FIG. 1,

(4) FIG. 3 is a schematic side view of a heating installation alternative to FIG. 1,

(5) FIG. 4 is a schematic side view of a heating installation alternative to FIG. 1 and

(6) FIG. 5 is a schematic side view of another embodiment alternative to FIG. 1.

(7) A schematic side view of a heating installation 11, particularly a high-temperature heating installation, is shown in FIG. 1. FIG. 2 shows a schematic view from underneath. The high-temperature heating installation 11 includes a substrate 12, which, for example, in use in the field of white goods, can be designed as ceramic, glass ceramic, Ceran ceramic, aluminium oxide ceramic or similar. On their underside, a heating element 14 is provided within a heating region. This heating element 14 includes a first electrically conductive layer 16, on which a protective layer 17 is applied. Preferably, the protective layer 17 completely covers the first electrical layer 16, so that this is provided as electrically insulated and mechanically protected against the environment on the substrate 12. The first electrically conductive layer 16 extends between two strip-shaped contact elements 18, which are guided up to an edge of the substrate 12, for example, for contacting the electrical layer 16. The first layer 16 extends between both contact elements 18, which are preferably running parallel to one another, and forms the heating region. The protective layer 17 covers the first layer 16, and preferably the strip-shaped contact elements 18, so that only in the edge region, for example, a free contacting point can be omitted. Alternatively, it can also be intended that the first layer 16 and the protective layer 17 are applied first of all, and then the strip-shaped contact elements 18 are brought through the heating region formed by the first layer 16 and protective layer 17.

(8) The first electrically conductive layer 16 consists of a flowable, electrically non-conductive base material, which can flow. Dispersion on an aqueous basis is also preferably intended. In this dispersion, carbon-nanotubes are dispersed as electrically conductive material. In addition, the dispersion includes a filler, particularly graphite, in order to support the electrical conductivity and to set flow capability. An adhesive agent is also preferably provided in the dispersion. This can be gum arabic, for example. Other surfactants such as SDS or triton can also be used. Through this, a pasty or flowable mass can be produced, which can be applied onto the substrate 12 in a printing process or spraying process. This dispersion is resistant to high-temperatures, thermal shock and is hydrophobic. The protective layer 17 preferably consists of a silicate, which can preferably be enriched with an adhesive agent, filler or other particles, in order to increase the adhesive qualities. Through this, the thermal shock stability as well as the mechanical bonding to the substrate can be improved. Due to the protective layer 17 penetrating into the first layer 16, these carbon nanotubes are also suitable for use at temperatures above 350 C., since the protective layer 17 seals the carbon nanotubes in an airtight manner. The electrically conductive material preferably consists of a compound of carbon nanotubes and graphite or other electrically conductive particles or components, which facilitate the forming of a pasty matter or matter, which can be sprayed.

(9) The heating element 14 shown in FIG. 1 is produced by the components of an electrical non-conductive base material and carbon nanotubes dispersed therein, or a compound of carbon nanotubes first of all being mixed with other electrically conductive materials, in order to form a pasty or flowable mass, which is applied onto the whole surface of the substrate by means of a screen printing process. Subsequently the strip-shaped contact elements 18 can be imprinted in a screen printing process, preferably by application of a conductive paste, particularly silver conductive paste. These contact elements 18 can also be provided on the substrate 12 before the application of the first layer 16. Subsequently, according to a variant of the first embodiment of the production process, this first layer 16 can be temperature-treated. This has the advantage that a hardening and drying up of the base material or the aqueous basis for the first layer 16 formed as dispersion takes place, which increases subsequent penetration of the protective layer 17. The protective layer is preferably applied by a screen printing process. Alternatively, this can also be applied without an intermediary drying process of the first layer 16. Subsequently the substrate 12 with the layers 17 applied thereon as well as the contact elements 18 are temperature-treated, so that at least the protective layer 17 is preferably sintered. Here the compression takes place and causes the conductive particles to be further pressed together, which leads to a lower spec. resistance due to the increased contact number and the compactness. This can also result in improving the conductivity in the first layer 16.

(10) High-temperature heating installations 11 comprise heating elements 14, of which the thickness can be <100 m, for example. In addition, due to the full-area arrangement of the electrically conductive layer 16 on the substrate 12, homogeneous heating and heat radiation 12 are made possible.

(11) The protective layer 17 can preferably be assigned to a reflector, in order to reflect the heat radiation coming from the heating element 14 in the opposite direction to the substrate 12, and to accelerate the heating of the substrate 12.

(12) An embodiment alternative to FIG. 1 is shown in FIG. 3, and to the effect that instead of successive application of the first layer 16 and the protective layer 17, a functional layer 21 is applied. This functional layer 21 is produced from the same base material as the protective layer 17. A silicate, particularly ethyl silicate, in which carbon nanotubes are dispersed, is used here. This functional layer 21 to the carbon nanotubes can preferably include other conductive particles, and particularly a binding agent, preferably graphite, as a further component. By means of a functional layer 21 of this type, it is made possible for a pasty matter to be given, which can be applied by a spraying process or a screen printing process. Furthermore, by means of the subsequent heating, a compression of this layer by a sinter process is also achieved, whereby the conductivity is increased. This alternative embodiment simplifies production of a heating element 14 of this type, whereby at the same time the requirements for operation at temperatures of >400 C. as well as mechanical bonding and thermal stability are also given. The strip-shaped contact elements 18 can be applied onto the substrate 12 before or after the application of the functional layer 21.

(13) An embodiment alternative to FIG. 1 is shown in FIG. 4. This embodiment differs from that in FIG. 1, in that before the application of the first electrically conductive layer 16, an electrical insulating layer 19 is applied over the whole area of the substrate 12, in order to arrange the electrically conductive layer 16 in an insulated way with regard to the substrate 12. This arrangement of the insulating layer 19 can also be intended in the event of applying a mixture consisting of the first electrically conductive layer 16 and the protective layer 17. Also, before the application of the functional layer 21 onto the substrate, an electrically insulating layer 19 can be applied over the whole surface.

(14) An embodiment alternative to FIG. 1 is shown in FIG. 5. This embodiment only differs in that instead of a full-area first electrically conductive layer 16, a strip-shaped layer 16 is formed. Bars or ribs can be adapted in geometry and contour to the corresponding cases of use. The strip geometry can heat specific areas. In addition, it favours the bonding qualities on the respective substrate. The strips can be arranged in any way, so that on a substrate, specifically different heating zones can be implemented.