EP4205505A1

EP4205505A1 - Flexible heating element, method for producing such a heating element, and use of a flexible heating element

Info

Publication number: EP4205505A1
Application number: EP21763093.8A
Authority: EP
Inventors: Tim Asmus; Matthias Muziol; Christoph Nick; Stefan Dietmann; Karlheinz Wienand; Carsten Neemann
Original assignee: Yageo Nexensos GmbH
Current assignee: Yageo Nexensos GmbH
Priority date: 2020-08-27
Filing date: 2021-08-20
Publication date: 2023-07-05
Also published as: US20230328847A1; KR20230043970A; CN116133540A; JP2023539080A; WO2022043210A1; DE102021104002A1; EP3962234A1

Abstract

The invention relates to a flexible heating element (10) exhibiting a temperature resistance of at least 250°C, in particular of at least 300°C, comprising: - an electrically conductive substrate (15) formed from a metal foil, - an insulation layer (20) formed on at least one side (16) of the substrate (15), and - a heating structure (30) formed on the side (21) of the insulation layer (20) facing away from the substrate (15), wherein the heating element (10) has a heating-element thickness (DH) of less than 1.0 mm, the substrate (15) has a substrate thickness (DS) of 0.02 mm - 0.5 mm, and the insulation layer (20) has an insulation-layer thickness (DI) of 0.2 µm - 30 µm.

Description

DESCRIPTION

Flexible heating element, method for manufacturing such a heating element and use of a flexible heating element

The invention relates to a flexible heating element with a temperature resistance of at least 250°C, in particular at least 300°C. Furthermore, the invention relates to a method for producing such a heating element. The invention also relates to the use of a flexible heating element according to the invention.

Different embodiments of heating elements are known from the prior art. US 2018/0093455 A1, for example, discloses a flexible, flat heater which is based on a polymer laminate. The laminate consists of a polymer layer, specifically polyimide, a primer layer and a silicone adhesive layer. A Meta II structure, which is designed as a heating structure, is laminated on the silicone adhesive layer. A disadvantage of such heating elements, however, is the use of a polymeric laminate. Use of such materials prevents use of the heating element at temperatures above 300°C. This is due to the fact that the polymers of the laminate would pyrolyze or degrade at such temperatures.

US Pat. No. 5,408,574 A in turn discloses a heating element which is based on the use of a ceramic substrate. The ceramic substrate has a thickness of 25-250 μm in order to guarantee sufficient stability. The heater has individual heating structures that can be controlled individually. These heating structures are preferably produced by means of screen printing on the basis of a paste containing noble metals. Such a heating element is designed in such a way that it reaches a temperature of 450 °C - 600 °C in two seconds with a maximum heating power of 10 - 20 W. The disadvantage of such a heating element, however, is the use of a ceramic substrate. Such ceramic substrates are neither elastic nor do they have a high breaking strength.

Proceeding from the above, it is the object of the present invention to specify such a solution which has a flexible heating element on the one hand and high temperature resistance on the other hand. A flexible design of a heating element is particularly advantageous for establishing good thermal contact with bodies in contact with uneven surfaces.

Furthermore, it is the object of the present invention to specify a method with the aid of which a flexible heating element can be produced. A further object of the invention consists in specifying a corresponding use of the heating element according to the invention.

According to the invention, this object is achieved with regard to a flexible heating element by the subject matter of claim 1, with regard to a method for producing a heating element according to the invention by the subject matter of claim 11 and with regard to a use of a heating element according to the invention by the subject matter of patent claim 15.

The invention is based on the idea of specifying a flexible heating element with a temperature resistance of at least 250° C., in particular at least 300° C., the flexible heating element comprising:

• an electrically conductive substrate formed from a metal foil,

• an insulating layer formed on at least one side of the substrate, and

• a heating structure formed on the side of the insulating layer pointing away from the substrate, the heating element having a heating element thickness of less than 1.0 mm, the substrate having a substrate thickness of 0.02 mm-0.5 mm and the insulating layer having an insulating layer thickness of 0.2 μm - has 30 pm.

In other words, a heating element is specified which on the one hand is flexible and on the other hand has a high temperature resistance of at least 250° C., in particular at least 300° C. The formation of such a heating element is made possible by the fact that the individual layers or components of the flexible heating element are further developed in terms of their materials and the respective thicknesses of the elements or layers such that flexibility is produced on the one hand and temperature resistance on the other.

In a particularly preferred embodiment of the invention, the heating element has a heating element thickness of less than 0.6 mm, particularly preferably less than 300 μm. Electrically insulating layers that electrically isolate the electrically conductive substrate from the heating structure are particularly suitable as insulating layers. In general, layers with a specific resistance of > 10E10 Q * cm are suitable for this.

The insulation layer preferably comprises a metal oxide layer, in particular an anodized metal oxide layer, or a metal nitride layer or a metal oxynitride layer. In a particularly preferred embodiment of the invention, the insulation layer is a metal oxide layer, in particular an anodized metal oxide layer, or a metal nitride layer or a metal oxynitride layer. If the insulation layer is one of the metal layers mentioned, the insulation layer has no further layers that do not fall under the preceding layer definitions.

Furthermore, it is possible for the insulation layer to be designed as a combination of different metal oxide layers, metal nitride layers or metal oxynitride layers stacked on top of one another.

The advantage of an insulation layer that is or has a metal oxide layer, a metal nitride layer or a metal oxynitride layer is that such insulation layers have both good insulating properties and can also be made as thin as possible.

Some metals, such as aluminum or FeCrAI alloys, form particularly stable metal oxide layers, so that the insulation layer does not flake off or cracks form in the insulation layer, even in the event of rapid temperature changes.

Furthermore, it is possible that the insulation layer has the following components:

Aluminum oxide (AI2O3) and/or aluminum titanate (AhTiOs) and/or titanium dioxide (TiC>2) and/or silicon dioxide (SiC>2) and/or silicon oxide (SiO) and/or magnesium oxide (MgO) and/or magnesium titanate (MgTiCh) and/or a binary zirconia alloy and/or a ternary zirconia alloy and/or boron nitride (BN) and/or aluminum nitride (AIN) and/or silicon nitride (SisN^.

In a further embodiment of the invention, it is possible for the insulation layer to be produced using an ADM process (aerosol deposition method). With the help of one Method ceramic or glass-like insulation layers can be produced. These layers have a particularly high level of electrical insulation and can also have a thin layer thickness. If the insulation layer is produced using the ADM process, the thickness of the insulation layer can be 0.2 μm - 10 μm.

In addition to the ADM method, other known deposition methods such as CVD (chemical vapor deposition) or CSD (chemical solution deposition) or PVD (physical vapor deposition) are also possible for applying an insulating layer to a metal foil.

The electrically conductive substrate is formed from a metal foil. In particular, the electrically conductive substrate consists of a metal foil.

The metal foil is preferably formed from such materials that form dense metal oxide layers with high electrical insulation during anionic oxidation. This serves to produce a corresponding insulation layer. Foils made of aluminum, steel, titanium, niobium or tantalum are therefore particularly suitable as metal foils. With regard to the steel foils, alloys containing chromium and aluminum are particularly suitable.

The metal foil is preferably formed from aluminum (Al) and/or steel and/or titanium (Ti) and/or niobium (Nb) and/or tantalum (Ta) or their alloys.

The steel is preferably an FeCrAI alloy, in particular X8CRAI20-5 or FeCr25AI5.

The substrate thickness is 0.02 mm - 0.5 mm, in particular 0.05 mm - 0.3 mm.

Due to the use of metal foils for the production of an electrically conductive substrate, in particular when using an aluminum foil, distortion of the metal foil during the heating up of the flexible heating element is prevented.

The use of a metal foil to form an electrically conductive substrate also has the advantage that, for example, in contrast to the use of polymeric substrates, the insulation layer can be applied using variable methods.

Since the metal foil can be exposed to high temperatures, the insulation layer can also be applied by means of such a method, with a high accompanied by temperature exposure. This is the case, for example, when applying metal-containing pastes. Such pastes or layers of sintering paste are regularly to be sintered at high temperatures of, for example, 1000.degree. Due to the use of a metal foil, such thermal loads can be applied without further ado.

An anodized metal oxide layer differs from an atmospheric metal oxide layer in having higher electrical insulation. An anodized metal oxide layer can be produced, for example, by anodizing a metal surface. In other words, an insulating layer that is an anodized metal oxide layer can be produced by anodizing the metal surface of the substrate. Due to electrolytic oxidation, the surface of the metal foil is converted into a metal oxide layer.

A further advantage of forming an insulating layer on the basis of a thermally or anodically oxidized substrate relates to the connection of the insulating layer to the substrate. An insulation layer produced or provided in this way has a higher connection to the substrate than is the case, for example, by means of subsequently applied ceramic layers. Thermally oxidized, in particular anodized, substrates can also be mechanically processed, in particular punched, after the thermal oxidation process has been carried out, in particular after an anodizing process has been carried out. With this mechanical processing, especially with punching, the insulation layer is not further damaged. In fact, in this case, the insulation layer is prevented from flaking off.

An anodizing process is a surface technology method for producing an oxidic protective layer through anodic oxidation. In contrast to galvanic coating processes, the protective layer is not deposited on the workpiece, but rather an oxide or hydroxide is formed by converting the top metal layer. A 5 pm - 25 pm thin layer is formed, which protects and insulates the underlying layers or elements, namely the substrate.

Another way to produce a metal oxide layer is a hard anodizing process. As in the anodizing process, the metal foil is immersed in an electrolyte and connected as an anode. The surface of the metal foil is oxidized in the process, so that a metal oxide layer is formed. In this case, the volume of the metal foil increases. By appropriately selecting the material of the metal foil of the electrically conductive substrate, an appropriate selection can be made with regard to the insulation layer to be formed thereon.

Prior to oxidation of the metal surface, surface pretreatment steps such as etching, pickling, honing, electropolishing, mechanical polishing, sandblasting, particle blasting, or grinding may be performed. A combination of several of the pretreatment steps mentioned is also possible.

When using a steel foil made of an FeCrAl alloy, oxidation of this layer in air at elevated temperatures can also produce a metal oxide layer.

When using an FeCrAl alloy with an aluminum content of 6%, for example, an electrically insulating insulation layer, in particular an electrically insulating aluminum oxide layer, of up to 5 μm can be produced in an oxygen-containing atmosphere in a furnace at oxidation temperatures of 1,000° C. to 1,100° C .

In a further embodiment of the invention, it is also possible to use steel foils with a low CrAl content, provided such a steel foil is aluminated on at least one surface or on at least one side. An alitizing process provides that a layer containing aluminum is applied to the substrate metal foil, with this layer containing aluminum then being annealed at temperatures of 800 °C to 1,200 °C. This results in dense A^Os layers with a thickness of > 20 pm. The AhOs layer is in the a phase. Due to this process, an insulating layer is formed on at least one side of the substrate. Such an insulation layer is an electrically insulating metal oxide layer.

A flexible heating element is to be understood in particular as a heating element that can be deflected in a direction perpendicular to a front side or a rear side without the deflection leading to a significant change in resistance and/or cracks and/or fractures and/or similar damage to the heating element leads. Heating even when bent is expressly possible.

The flexibility of the heating element is a reversible deflection of a front or a back of the heating element with a bending radius of at least 30 mm, in particular of at least 25 mm, in particular at least 20 mm, in particular at least 10 mm, in particular at least 0.5 mm.

Reversibility also means that a metal foil that has already been deformed also has a spring effect. After a forced additional bending of the metal foil, it returns completely or at least partially to its pre-embossed starting position. Due to the spring effect, a curved heating element can independently exert a force on surrounding parts after it has been installed in a holder and thus nestle against them.

The at least one heating structure is preferably applied directly to the insulation layer. In other words, the at least one heating structure is applied directly to the side of the insulation layer facing away from the substrate. In such an embodiment of the invention, no further layers are formed between the heating structure and the side of the insulating layer pointing away from the substrate.

In a preferred embodiment of the invention, the heating structure is not in direct contact with the substrate. In other words, the heating structure is completely electrically isolated from the substrate by forming the insulating layer. The heating structure is preferably not in contact with the electrically conductive substrate.

However, embodiments are also possible in which adhesion promoter layers, such as titanium/titanium oxide or tantalum/tantalum oxide layers, are formed between the insulation layer and the heating structure.

Preferably, the heating structure consists of a Meta II structure. The heating structure preferably has an electrical resistance of 0.5 to 30.0 Ω, in particular 0.5 to 10.0 Ω. The electrical resistance is formed between two terminals of the heating structure.

The heating structure describes such a structured element that triggers the actual heating process of the flexible heating element.

The heating structure, made in particular of a metal structure, can have any shape. For example, it is possible to form a heating structure in a square shape. It is also possible to form a heating structure with an essentially straight line structure. In particular, the heating structure has a meandering shape. Such a meandering shape can be formed, for example, from a coherent, interwoven and/or nested and/or interlocking line structure.

The individual sections, in particular the individual line sections, can be made relatively thin.

The heating structure, which is present in particular in a meandering form, can cover an area of any size due to the structure formed. Such a large area of the object to be heated leads to a homogeneously generated surface temperature.

The heating structure can be formed from a structured metal foil. If such an embodiment with regard to the heating structure is present, the heating structure can be produced in a separate process and then applied to the insulation layer.

In a further embodiment of the invention, the heating structure, which is preferably formed from a structured metal foil, can be laid floating on the insulation layer and fixed to the insulation layer.

Furthermore, it is possible for the heating structure to be produced from a metal-containing paste and/or a metal-containing ink. Such a metal-containing paste and/or ink can be applied to the insulation layer as part of a printing process, in particular as part of a screen printing process.

In a particularly preferred embodiment of the invention, the heating structure is made from a paste containing noble metals. In particular, the noble metals can be platinum and/or silver and/or gold.

In a further embodiment of the invention, the heating structure is a Meta II structure produced by means of thin-film metal deposition.

The at least one heating structure preferably has at least two contact pads or is connected to at least two contact pads. The at least two contact pads are preferably formed on the side of the insulation layer facing away from the substrate. If the heating structure of the flexible heating element has no contact pads, the heating structure has at least two connections, each of which has to be electrically connected to the outside.

In a further embodiment of the invention, on the heating structure, i. H. a passivation layer can be formed at least in sections on the side of the heating structure pointing away from the substrate. Such a passivation layer is preferably a glass and/or ceramic layer. It is possible for the passivation layer to have polymer materials, in particular crosslinked polymers.

In one possible embodiment of the invention, the passivation layer is produced using an ADM (aerosol deposition method) process.

Furthermore, it is possible that the flexible heating element is completely surrounded by a passivation layer, in particular by an electrically insulating glass and/or ceramic layer, or is encapsulated in such a layer. In such an embodiment of the invention, formed contact pads and/or connections of the heating structure are to be left uncovered at least in sections by such a passivation layer. In other words, at least the two contact pads and/or at least two connections of the heating structure are not completely coated with a passivation layer.

In a further embodiment of the invention, the heating structure can be formed between two substrate sections, the two substrate sections being formed by folding the substrate. Such an embodiment of the invention enables good heat transfer between the heating structure and the substrate.

Furthermore, it is possible for the heating structure to be formed between two substrate sections, with the substrate sections being formed separately from one another. In other words, the heating structure can be formed between two separate substrate sections such that a sandwich structure is formed. Such a design of a heating structure formed between two substrate sections is possible in particular when using, in particular superficially, oxidized metal foils as the substrate. A connection of the substrate parts can also be produced by roll cladding or laser welding. The internal heating structure can also be held and pressed against one another by bracing at least two substrate parts will. Such embodiments of the invention enable good heat transfer between the heating structure and the substrate.

In a further embodiment of the invention, the substrate sections can be designed differently. This applies, for example, to the materials of the substrate sections. It is possible that differently oxidized metal foils form two different substrate sections. In such an embodiment of the invention, the flexible heating element can be specifically specified and adapted to the respective installation situation or with regard to the specific area of application.

If a heating structure is formed between two separate substrate sections, two insulating layer sections are also formed. The insulating layer sections are formed separately from each other or formed by folding a single insulating layer. In other words, the heating structure is formed between two insulating layer sections, the insulating layer sections in turn being formed between two substrate sections.

It is possible for the insulation layer sections to be welded to the substrate sections, in particular welded at certain points.

The flexible heating element according to the invention with a temperature resistance of at least 250° C. has a flat design due to the material selection according to the invention and the layer thickness selection according to the invention. Such a flat design enables the flexible heating element to be used in structurally restricted applications.

With the help of the flexible heating element according to the invention it is possible to have larger surfaces, i. H. form larger front and / or back sides of the flexible heating element. Because of such large surfaces or large front and/or rear sides, good heat transfer from the flexible heating element to an object to be heated is possible.

In one possible embodiment of the invention, the flexible heating element is not flat. The flexible heating element can be curved, for example. In one possible embodiment, the flexible heating element is bent into a hollow body. In other words, the flexible heating element has the shape of a hollow body, in particular the shape of a cylinder.

If the flexible heating element is designed as a hollow body, in particular in the form of a cylinder, the hollow body has a round cross section. The cross section is preferably at least 2 mm, in particular at least 3 mm. With the help of the flexible heating element it is therefore possible to provide such a heating element which can be positioned in small components. In particular, it is possible to use a flexible heating element according to the invention in an electric smoking device.

In order to form a flexible heating element in the hollow body, in particular in the form of a cylinder, two side edges of the substrate are bent towards one another, for example. The side edges then pointing to one another can, for example, be arranged so that they rest against one another.

Furthermore, it is possible for the side edges of the substrate, which point towards one another due to the bending of the flexible heating element, to be designed to overlap or be spaced apart from one another. If the side edges pointing to one another are spaced apart from one another, a cylindrical shape with a longitudinal gap is formed. The actual arrangement of the mutually facing side edges can be designed variably depending on the later installation situation or depending on the area of application of the flexible heating element.

It is also possible, if the flexible heating element has a curved design, to lock the flexible heating element in the curved shape by means of a fastening element. In other words, the flexible heating element can have a fastening element, the curved shape of the flexible heating element being maintained by means of the fastening element.

In one embodiment of the invention, the fastening element can be designed in the manner of a flange. Such a flange-like fastening element can have the form of a ring or a sleeve. The flange-like fastening element can be made of metal or ceramic, for example. These materials have proven to be particularly thermally stable.

Due to the spring effect of the flexible heating element, it is particularly easy to the flexible heating element nestles against the flange-like fastening element, so that the shape of the flexible heating element can be easily maintained.

In a further embodiment of the invention, the fastening element can be designed in the manner of a cover. Such a cover or a cover-like fastening element is preferably arranged on at least one end of the hollow body formed, in particular of the cylinder formed. A cover-like fastening element is preferably pushed onto one end of the hollow body, in particular the cylinder, so that the cover-like fastening element stabilizes the hollow body, in particular the cylinder.

In a further embodiment of the invention it is possible to adapt or select the shape of the substrate of the flexible heating element in such a way that in a bent state of the flexible heating element, i. H. in the formation of a hollow body, in particular a cylinder, corresponding openings, in particular slots, are produced in the hollow body, in particular in the cylinder.

For example, it is possible for the substrate of the flexible heating element to have lateral recesses. For example, the substrate of the flexible heating element can have a meandering side edge profile. The lateral recesses of the substrate of the flexible heating element can extend up to the middle of the substrate.

Furthermore, it is possible for lateral recesses of the substrate to be formed on opposite side edges of the substrate in such a way that they alternately extend to the middle of the substrate or beyond the middle of the substrate.

In a further embodiment of the invention it is possible that a curved flexible heating element, in particular a hollow body-like, in particular a cylinder-like, flexible heating element is arranged in a sleeve. Such a sleeve can also be referred to as a cover sleeve. The sleeve is preferably made of metal, in particular aluminum or steel. Such a sleeve, in particular such a cover sleeve, protects the flexible heating element. In a preferred embodiment, the sleeve is electrically isolated from the heating element or at least from the conductor track located on the heating element. In the preferred embodiment, the sleeve is heated by the flow of heat through the mechanical contact between the heating element and the sleeve. In a particularly preferred embodiment, the curved heating element is pressed against the sleeve wall by its own spring force. The flexible configuration allows improved thermal contact between the flexible heating element and an object to be heated with an uneven surface, and thus rapid and energy-efficient heating of the object.

The formation of an insulating layer from the specified materials and with the specified layer thicknesses enables rapid and energy-efficient heating of the substrate.

Due to the choice of material and/or layer thickness in connection with the flexible heating element, the heating element also has a low thermal mass, so that rapid and energy-efficient heating of the heating element is made possible.

A further aspect of the invention relates to a method for producing a flexible heating element according to the invention. With regard to individual aspects of the method, reference is made to the explanations in connection with the heating element according to the invention. In the preceding part of the description, individual aspects relating to the production of the heating element are already contained.

The method according to the invention for producing a heating element according to the invention comprises the steps: a) providing a substrate which is formed from a metal foil, b) forming at least one insulating layer on at least one side of the substrate, and c) applying a heating structure to the side facing away from the substrate the insulation layer.

In step b), to form the insulating layer: an anodized metal oxide layer is produced by means of an anodizing process or hard anodizing process, or an oxidation process is carried out at an oxidation temperature of at least 800° C., or an aluminum layer is applied to at least one side of the substrate and an aluminum oxide layer is then produced by means of oxidation at temperatures of 800 °C to 1,200 °C, or an electrically insulating layer by means of ADM processes or CVD processes or CSD processes or PVD processes on at least applied to one side of the substrate.

In step c), for applying the heating structure: a structured metal element, in particular a structured metal foil element, is applied to the insulation layer, or the heating structure is formed on the insulation layer by means of a thin-film metal deposition, or the heating structure is formed on the insulation layer by printing a metal-containing paste or a metal-containing ink educated.

A further embodiment of the method according to the invention provides for a passivation layer to be applied at least in sections to the heating structure.

A passivation layer is preferably applied to the entire upper side of the heating structure. If the heating structure has contact pads, the contact pads are provided with a passivation layer at most in sections. The contact pads are preferably formed completely without a passivation layer. This makes it possible to make electrical contact with the contact pads in a correspondingly simple manner.

The method according to the invention for producing a heating element is characterized by a particularly simple method and a cost-effective implementation.

In a further embodiment of the method according to the invention, steps a) to c) are carried out on a substrate strip and/or a substrate plate.

The shapes of individual substrates are applied to the substrate strip and/or the substrate plate. For this purpose, the substrates on the sides of the substrate tape and/or the substrate plate separately. The substrates are not detached from the substrate band and/or the substrate plate at corners and/or individual side sections, so that the individual substrates continue to be connected to the substrate band and/or the substrate plate.

The individual substrates can then be processed further in this form, so that steps b) and c) can be carried out together.

Finally, the individual substrates are separated from the substrate belt and/or the substrate plate.

The method according to the invention for producing a heating element according to the invention can also include step d). In step d), the substrate can be mechanically processed with regard to its shape. In step d), the substrate can be cut and/or punched. Step d) can be carried out between steps b) and c).

Alternatively, it is possible for step d) to be carried out after step c). In other words, mechanical processing of the substrate can also be carried out after a heating structure has been applied to the insulation layer. Such an execution of step d) is possible in particular if the insulation layer is formed from the substrate as a result of an oxidation process. In particular, this is possible if a thermal oxidation process or an anodizing process is used to produce the insulating layer.

Due to the possibility of carrying out step d), it is possible to design the shape of the flexible heating element variably, with no restrictions to the effect that the shape must already be taken into account during production of the substrate.

This simplifies the production of a heating element according to the invention.

A further aspect of the invention relates to the use of a flexible heating element according to the invention. The use according to the invention provides for the use of the flexible heating element in combination with a temperature sensor and/or in combination with a temperature sensor chip and/or in an electric smoking device. It is possible to use the flexible heating element according to the invention as a temperature sensor. In such an application, the resistance of the heating structure is measured, it being possible to detect the temperature to be measured by means of a temperature-resistance characteristic.

Furthermore, it is possible for the flexible heating element to have a temperature sensor. The temperature sensor can be arranged on the insulating layer of the flexible heating element. It is possible for the temperature sensor to be designed in the form of a Meta II structure, in particular in the form of a platinum structure.

Furthermore, it is possible for a temperature sensor chip to be integrated on and/or in the flexible heating element.

The flexible heating element according to the invention can be used in particular for heating and tempering objects of any kind. This is due to the advantageous flexible and at the same time temperature-resistant design of the flexible heating element.

Particularly preferably, the flexible heating element can be used for rapid heating of flat objects with a small mass or of liquids or gases. The flexible heating element can in such a case be pressed against the (flat) surface of the object to be heated to enable effective heat transfer. The force for pressing the heating element to its surroundings can also be based on the spring action of a bent heating plate.

Due to the flat and flexible design of the flexible heating element, the heating element according to the invention can also be used in arrangements that should not be brought into contact with thick or rigid heating elements. An example is the use of flexible heating elements in cell stacks, such as fuel cells or battery packs.

Furthermore, it is possible to apply the heating element according to the invention to electronic components such as semiconductors or sensors. Electronic components such as semiconductors or sensors can be heated to a desired operating temperature with the aid of the heating element according to the invention and the corresponding operating temperature can then be maintained. A further use of a flexible heating element according to the invention is the use in combination with textiles and/or items of clothing.

Furthermore, the flexible heating element can be used as a heating head and/or heating strip for laminating or welding plastics.

Furthermore, a flexible heating element according to the invention can be used in an electric smoking device. Preferably, it is an electric smoking device for combustion-free smoking of herbal substances such. As tobacco, or organic liquids or alcoholic extracts. The liquids can be, for example, nicotine-containing solutions.

If the electric smoking device is to be used for combustion-free smoking of herbal substances, herbal substances are pressed into a pad and mixed with additives, such as e.g. B. glycerin, added. Such a pad is placed on a flexible heating element of the electric smoking device and is pressed onto the flexible heating element by means of a mechanical lock.

Due to the flexibility of the heating element, the heating element adapts to the surface shape of the pad and forms good thermal contact. The flexible heating element is electrically heated to temperatures of up to 300 °C in order to be able to extract the pad's ingredients without burning them.

Since the flexible heating element has no polymers or other organic compounds, no organic decomposition products are produced when the flexible heating element is heated, which are detrimental to the inhalation of the aerosols produced.

If the electric smoking device is used for smoking liquids without combustion, the liquid is transported from a reservoir in the direction of the surface of the flexible heating element and vaporized there. In particular, the liquid gets from the reservoir to the surface of the flexible heating element with the aid of a wick or a porous body. In the following, according to Embodiments 1 to 5, various flexible heating elements and various methods for manufacturing these flexible heating elements are given.

Embodiment 1:

The flexible heating element includes an electrically conductive substrate formed from anodized aluminum foil. The substrate has a substrate thickness of 100 μm. The insulating layer is formed from the aluminum oxide layer. The insulation layer thickness is approx. 5 pm. The aluminum oxide layer has a high level of electrical insulation between the surface of the oxide and the metallic core of the metal foil. This applies in particular to low electrical voltages.

The heating structure is formed from a metal foil, specifically a nickel-chromium (NiCr) foil. The heating element thickness is approx. 50 μm. The heating structure is designed in such a way that a meander with a line width of 1 mm and a length of 50 mm is punched out of the nickel-chromium foil (specific resistance Ro=132 pΩ*cm). At the respective ends of the heating structure, i. H. at the connections, there are contact pads. These contact pads have a width of 5 mm. There is an electrical resistance of 1.3 Ω between the two contact pads.

After the heating structure has been produced, the heating structure is placed on the side of the insulation layer (aluminum oxide layer) facing away from the substrate. The metal foil (aluminum foil) is then folded, so that the heating structure is formed or arranged between two substrate sections. The heating structure lies loosely in a pocket made of anodised aluminum foil and can be moved freely in this pocket.

The structure present in this way can be arched in order to fix the heating structure in the substrate pocket formed. Furthermore, good heat transfer between the heating structure and the substrate is ensured due to the curvature.

Embodiment 2:

The structure of the substrate and the insulation layer corresponds to the structure according to embodiment 1.

The heating structure is made of an iron-nickel (FeNi) foil (Ro=72 pQ * cm).

The electrical resistance of the heating structure is consequently 0.72 Ω. The advantage of such a Material selection related to the heating structure is that iron-nickel has a high positive temperature coefficient of resistance and consequently the heating structure has self-regulating properties.

This means that the electrical resistance of the heating structure increases with increasing temperature and overheating of the heating structure is prevented.

Embodiment 3:

The substrate and the insulating layer are manufactured according to the structure described in Embodiment 1. The heating structure is made by screen printing. For this purpose, a silver sinter paste is applied through a sieve to one of the sides of the insulating layer facing away from the substrate. The silver sinter paste can also contain metal oxides and/or organic components and/or ground glass frit.

The silver sinter paste is then baked at a temperature of approx. 400 °C. Due to the use of a metal foil, in particular an aluminum foil, as the electrically conductive substrate, exposure to such a temperature is possible.

Embodiment 4:

According to this embodiment, a so-called KAT sheet metal is used as the substrate. Such a sheet is formed from an iron-chromium-aluminum (FeCrAl) alloy. To form an insulating layer, the KAT sheet metal is oxidized at over 1,000 °C, in particular at 1,050 - 1,200 °C in air. The edges of the sheet are thus also oxidized. The heating structure can then be applied to the insulation layer as a silver sinter paste.

Embodiment 5:

Embodiment 5 also provides for the use of a KAT sheet. The individual substrates, which preferably have a rectangular shape, are separated from a panel consisting of a sheet of KAT sheet metal, without completely detaching it from the panel. Such an arrangement is made by separating the individual substrates from the panel at their sides. The individual substrates remain connected to the panel at the corners. The substrates can be further processed in this arrangement, ie in the state associated with the panel. In particular, the anodizing and the application of a heating structure to the individual substrates can be carried out in a single step for all substrates. The substrates can be separated from the panel, for example, by means of punching and/or laser cutting.

The invention is explained in more detail below using exemplary embodiments with reference to the accompanying drawings.

In these show:

1a shows a flexible heating element according to the invention in a plan view;

1b shows the flexible heating element in a side view; and

2 shows a further embodiment with regard to a flexible heating element.

The flexible heating element 10 according to the invention essentially comprises five layers or elements.

The heating element 10 has a substrate 15 , an insulation layer 20 , a heating structure 30 , contact pads 31 and 32 and a passivation layer 40 .

The flexible heating element 10 has a temperature resistance of at least 250°C.

The electrically conductive substrate 15 is formed from a metal foil. The substrate has a first side 16 facing up and a second side 17 facing down.

An insulating layer 20 is formed on the first side 16 of the substrate 15 . The insulation layer 20 in turn has a first side 21 and a second side 22 . The second side 22 rests on the substrate 15 in this case. In contrast, the first side 21 of the insulation layer 20 faces away from the substrate 15 .

A heating structure 30 is formed on the side 21 of the insulating layer 20 facing away from the substrate 15 . The heating structure 30 has a meandering shape. Preferably this Heating structure 30 formed as a structured metal foil element. This metal foil element 30 can be applied to the first side 21 of the insulation layer 20 .

A passivation layer 40 is additionally applied to the side 33 of the heating structure pointing away from the substrate 15 or the insulating layer 20 . Due to the meandering shape of the heating structure 30, the passivation layer 40 also reaches the sections of the side 21 of the insulation layer 20 that are not covered with a heating structure 30.

The heating structure 30 has contact pads 31 and 32 at both ends or is connected to these contact pads 31 and 32 . The passivation layer 40 completely covers the heating structure. Furthermore, the contact pads 31 and 32 are partially covered by the passivation layer 40 .

The heating element thickness DH shown is less than 1.0 mm. The substrate 15 has a substrate thickness DS of 0.02 mm to 0.5 mm. The insulation layer 20 has an insulation layer thickness DI of 0.2 μm to 30 μm.

The heating element 10 is flexible, with the flexibility of the heating element 10 as a relative deflection of the front side 11 or the rear side 12 of the heating element 10 with a bending radius of at least 30 mm, in particular at least 25 mm, in particular at least 20 mm, in particular at least 10 mm, in particular at least 0.5 mm, is defined.

The flexible heating element according to the invention is produced according to the following method steps: a) First, the substrate 15, which is formed from a metal foil, is provided. The metal foils used are preferably foils made from materials which form dense metal oxide layers with high electrical insulation during anionic oxidation. Aluminum, steel, titanium, niobium or tantalum foils are particularly suitable as metal foils. Alloys containing chromium and aluminum are particularly suitable for steel foils. These are, for example, FeCrAI alloys. b) In this step, at least one insulating layer is formed on the first side 16 of the substrate 15. The insulation layer 20 is, for example, by anionic oxidation produced. Such an insulation layer 20 is an anodized metal oxide layer. c) In this step, the heating structure 30 is applied to the side 21 of the insulation layer 20 facing away from the substrate 20 . The heating structure 30 can be provided in an upstream process by producing a structured metal foil element. This can subsequently be applied to side 21 of insulating layer 20 .

The contact pads 31 and 32 can be formed as a section of the heating structure 30 . Alternatively, it is possible for the contact pads 31 and 32 to be made available as separate elements or components.

It is possible, for example, for the contact pads 31 and 32 to be formed from sintered paste material. Such a sintered paste material is applied to the side 21 of the insulation layer 20 . If the contact pads 31 and 32 are separate components, the heating structure 30 must be connected to the contact pads 31 and 32 .

Finally, a passivation layer 40 is applied to the upward-facing side 33 of the heating structure 30 . The contact pads 31 and 32 are also partially coated with the passivation layer 40 .

In Fig. 2 an alternative embodiment with regard to a heating element 10 is shown. It can be seen that a heating element 10 can also have a plurality of substrate sections, namely a first substrate section 15a and a second substrate section 15b.

The illustrated substrate sections 15a and 15b are formed separately from one another. The substrate sections 15a and 15b can be formed from different materials.

An insulating layer section 20a or 20b is in turn formed on a respective first side 16 of the respective substrate section 15a and 15b. The respective first side 16 of the substrate section is the inwardly directed sides. The second sides 17 of the substrate sections 15a and 15b each face outwards and thus form the outer surfaces of the heating element. FIG. 2 shows that the flexible heating element 10 can be bent. In particular, the heating element 10 can be further bent in such a way that the heating element 10 forms the shape of a cylindrical hollow body. Depending on the extent to which the side edges 18 of the substrate sections 15a and 15b are spaced apart from one another or are designed to overlap, for example, the hollow body, in particular the cylindrical hollow body, can also have a slot-shaped recess.

The heating structure 30 is formed between the two insulating layer sections 20a and 20b. Due to the design shown in FIG. 2, a type of sandwich arrangement of a heating element 10 is formed. The heating structure 30 is arranged by the electrically conductive substrate sections 15a and 15b in such a way that these are not in contact with one another or are not in direct electrical contact with one another.

The heating structure 30 is embedded between the insulation layer sections 20a and 20b in such a way that the insulation layer sections 20a and 20b each point towards one another on the first sides 21 or at least bear against one another in sections.

The individual layers of the heating element 10 can be connected to one another, for example, by the spot welds 50 shown. A flexible heating element 10 as shown in FIG. 2 is particularly suitable for use in an electric smoking device.

Reference List

10 heating element

11 Front heating element

12 Rear heating element

15 substrate

15a, 15b substrate sections

16 first side substrate

17 second side substrate

18 side edge

20 insulation layer

20a, 20b insulating layer sections

21 first side insulation layer

22 second side insulation layer

30 heating structure

31 first contact pad

32 second contact pad

33 side heating structure

40 passivation layer

50 spot weld

DH thickness heating element

DS thickness substrate

DI Thick insulation layer

Claims

25

EXPECTATIONS

1. Flexible heating element (10) with a temperature resistance of at least 250 ° C, in particular at least 300 ° C, comprising:

- an electrically conductive substrate (15) formed from a metal foil,

- an insulating layer (20) formed on at least one side (16) of the substrate (15), and

- A heating structure (30) formed on the side (21) of the insulating layer (20) pointing away from the substrate (15), the heating element (10) having a heating element thickness (DH) of less than 1.0 mm, the substrate (15) having a Substrate thickness (DS) of 0.02 mm - 0.5 mm and the insulation layer (20) has an insulation layer thickness (DI) of 0.2 pm - 30 pm.

2. Flexible heating element (10) according to claim 1, characterized in that the insulating layer (20) is a metal oxide layer, in particular an intrinsically grown or anodized metal oxide layer, or a metal nitride layer or a metal oxynitride layer.

3. Flexible heating element (10) according to claim 2, characterized in that the insulating layer (20) is aluminum oxide (Al2O3) and/or aluminum titanate (A^TiOs) and/or titanium dioxide (TiC>2) and/or silicon dioxide (SiC>2 ) and/or silicon oxide (SiO) and/or magnesium oxide (MgO) and/or magnesium titanate (MgTiCh) and/or a binary zirconia alloy and/or a ternary zirconia alloy and/or boron nitride (BN) and/or aluminum nitride ( AIN) and/or silicon nitride (SisN^.

4. Flexible heating element (10) according to one of the preceding claims, characterized in that the insulating layer (20) is produced by means of ADM processes (aerosol deposition method).

5. Flexible heating element (10) according to any one of the preceding claims, characterized in that the flexibility of the heating element (10) as a reversible deflection of a front side (11) or a rear side (12) of the heating element (10) with a bending radius of at least 30 mm, in particular at least 25 mm, in particular at least 20 mm, in particular at least 10 mm, in particular at least 0.5 mm, is defined. Flexible heating element (10) according to one of the preceding claims, characterized in that the metal foil is made of aluminum (AI) and/or steel and/or titanium (Ti) and/or niobium (Nb) and/or tantalum (Ta) or their alloys is formed. Flexible heating element (10) according to Claim 6, characterized in that the steel is an FeCrAI alloy, in particular X8CRAI20-5 or FeCr25AI5. Flexible heating element (10) according to one of the preceding claims, characterized in that the at least one heating structure (30) is applied directly to the insulation layer (20). Flexible heating element (10) according to one of the preceding claims, characterized in that the at least one heating structure (30) is formed between two substrate sections, the two substrate sections being formed by folding the substrate (15). Flexible heating element (10) according to one of the preceding claims, characterized in that the at least one heating structure (30) has at least two contact pads (31, 32) or is connected to at least two contact pads (31, 32), the at least two contact pads ( 31, 32) are formed on the side (21) of the insulating layer (20) facing away from the substrate (15). A method for producing a heating element (10) according to any one of claims 1 to 10, comprising the steps of: a) providing a substrate (15) formed from a metal foil, b) forming at least one insulating layer (20) on at least one side

(16) of the substrate (15), and c) application of a heating structure (30) to the side (21) of the insulating layer (20) facing away from the substrate (20). Method according to Claim 11, characterized in that in step b) for forming the insulating layer (20)

- an anodized metal oxide layer is produced by means of an anodizing process or hard anodizing process, or

- an oxidation process is carried out at an oxidation temperature of at least 800 °C, or

- An aluminum layer is applied to at least one side (16) of the substrate (15) and an aluminum oxide layer is then produced by means of oxidation at temperatures of 800° C.-1,200° C., or

- An electrically insulating layer is applied to at least one side (16) of the substrate (15) by means of ADM processes or CVD processes or CSD processes or PVD processes. Method according to Claim 11 or 12, characterized in that in step c) for applying the heating structure (30)

- a structured metal element, in particular a structured metal foil element, is applied to the insulating layer (20), or

- the heating structure (30) is formed on the insulating layer (20) by means of a thin-film metal deposition, or

- by printing a metal-containing paste or metal-containing ink Heating structure (30) is formed on the insulating layer (20). The method according to any one of claims 11 to 13, characterized by at least partially applying a passivation layer (40) on the

heating structure (30). Use of a flexible heating element (10) according to any one of claims 1 to 10, in combination with a temperature sensor and/or in combination with a temperature sensor chip and/or in an electric smoking device.