Hybrid printed heater with optional ptc effect

Abstract

A method of manufacturing an electric heating device (10), in particular for automotive applications, comprising the steps of: (42) cutting through a sheet (14) of a highly conductive material of a suitable thickness to obtain a predetermined line pattern (16) comprising at least one electrically conductive line (18, 20, 22), wherein electrically conductive bridge members (24, 26) interconnect portions of the at least one electrically conductive line (18, 20, 22), (46) depositing a layer of a curable adhesive material (28) onto a surface of a dielectric planar flexible carrier (12), (48) placing the obtained line pattern (16) onto the layer of adhesive material (28), (50) curing the adhesive material (28) under the line pattern (16) except for the adhesive material (28) under the bridge members (24, 26), (52) cutting through each bridge member (24, 26) at all ends between portions of the at least one electrically conductive line (18, 20, 22) interconnected by the respective bridge member (24, 26), and (54) removing the cut bridge members (24, 26).

Description

TECHNICAL FIELD

[0001] The present invention relates to the technical field of electric heating, in particular for automotive applications. More specifically, the present invention relates to electric heating of interior parts of a vehicle such as steering wheel, armrest, door, etc. BACKGROUND

[0002] Electric heating devices employing one or more electric heating members are widely used in the automotive industry to provide passenger comfort, e.g. by heating the overall vehicle cabin and / or the passenger seats and / or armrests and / or panels. Electric heating devices with flexible and / or stretchable heater members are known to be used in vehicle steering wheels to be heated immediately after the vehicle engine has been started in cold ambient conditions.

[0003] For such electric heating devices it is considered a requirement that the electric heating device should be inconspicuous for the vehicle user in the non-operational state. Other requirements can be a heat density as uniform as possible during operation, e.g. in the range of a few degrees Celsius, in order to avoid hot spots which can become conspicuous for the vehicle user and also to avoid material fatigue due to the occurrence of thermal stresses. A current requirement for such applications is of course miniaturization.

[0004] While having an excellent capability to carry high current densities, the requirements of these combinations typically exclude the use of conventional heating wires, e.g. made of copper.

[0005] To meet the above requirements, solutions have been proposed in the prior art employing foil heater members, i.e. heater members having the appearance of a thin flexible foil or film.

[0006] For example, international application WO2015 / 024909A1 describes a foil heater for heating a panel. The foil heater comprises a first spiral electrically resistive heating trace and a second spiral electrically resistive heating trace formed in a first layer and a second layer, respectively, which conform to a flat or curved surface. The first spiral electrically resistive heating trace and the second spiral electrically resistive heating trace can be manufactured by (rotary) screen printing, gravure printing, flexographic printing or inkjet printing of a conductive ink, followed by a curing / sintering step. Each of the first electrically resistive heating trace and the second electrically resistive heating trace has a center and at least one outer end. An electrically insulating layer is arranged between the first layer and the second layer. The electrically insulating layer comprises an opening accommodating an electrical via through which the first electrically resistive heating trace and the second electrically resistive heating trace are in electrical contact with each other. The foil heater is compatible with operation at lower temperatures. Due to its spiral shape, the heating traces can be densely routed over the entire heating surface with substantially no crossings. Thus, a significantly more uniform temperature distribution can be achieved.

[0007] Another approach has been taken by international application WO 2013 / 050621 A2, which describes an electrically conductive fabric for occupant sensing and / or heating applications, wherein sensors and / or heaters can be attached from the back side to surfaces such as driver seat, passenger seat, rear seat, steering wheel, door side of the vehicle cabin, gear lever, etc.

[0008] The flexible heater and / or electrode comprises a woven fabric material having a warp direction and a weft direction. The fabric material comprises at least one region having a low electrical conductivity and at least two regions having a high electrical conductivity. The at least two regions having a high electrical conductivity are adjacent to the at least one region having a low electrical conductivity. At least one of the at least two regions having a high electrical conductivity is operatively connected to a connection terminal of the heater and / or electrode, wherein the connection terminal is for connecting the heater and / or electrode to an electronic control circuit.

[0009] The resistive heating traces made by (rotary) screen printing, gravure printing, flexographic printing or inkjet printing of electrically conductive inks can easily be integrated close to the surface to be heated. Resistive inks with a positive temperature coefficient (PTC) are desirable because such materials are inherently self-limiting, and such resistive inks are readily available on the market. However, their use for the feeder lines is limited because the required sheet resistances can only be achieved with inks having a high silver loading. This has a large impact on cost efficiency and also results in a significant reduction in mechanical robustness in terms of resistance to bending of the printed conductor paths, because highly conductive silver inks are known to be mechanically fragile. Any compression, bending and / or elongation stresses that can be applied by an operator during installation, or for example by a seat occupant in the case of a seat heating device, can increase the resistance of one or more resistive heater elements due to cracks or fissures formed, resulting in a reduction of the heating power, up to a point where the electric heating device can eventually become inoperable. SUMMARY

[0010] It is therefore desirable to provide an improved electric heating device, in particular for automotive applications.

[0011] In one aspect of the invention, the object is achieved by a method of manufacturing an electric heating device, in particular for automotive applications, comprising at least the following steps:

[0012] providing a sheet of highly conductive material of a suitable thickness,

[0013] cutting through the sheet to obtain a predetermined line pattern, the predetermined line pattern comprising at least one electrically conductive line, wherein electrically conductive bridge members interconnect portions of the at least one electrically conductive line,

[0014] providing an electrically dielectric planar flexible carrier,

[0015] depositing a layer of a curable adhesive material onto a surface of a flexible carrier,

[0016] placing the obtained line pattern onto the layer of adhesive material,

[0017] the adhesive material under the cured line pattern, in addition to the adhesive material under the bridge members,

[0018] cutting through each bridge member at all ends between portions of the at least one electrically conductive line interconnected by the respective bridge member, and

[0019] removing the cut bridge members.

[0020] The term "automobile" as used in this patent application is to be understood in particular as applying to vehicles including passenger cars, trucks, semi-trailer trucks and buses.

[0021] The proposed method can enable a simple and cost-effective manufacturing of an electrical heating device, in particular for automotive applications, with an excellent capability to carry high current densities in the electrical feed lines forming part of a predetermined line pattern. The method allows manufacturing an electrical heating device, wherein the electrical heating members are based on a series circuit, and wherein the electrical feed lines as well as at least one electrical heating member are made of a sheet of highly conductive material. The bridge members, which are removed at the end of the manufacturing method, provide for better handling properties of the predetermined line pattern obtained after the step of cutting through the sheet, or even enable its handling. Furthermore, the method is able to manufacture an electrical heating device, which can be integrated with low visibility and haptically into the outer surface of a close-by object.

[0022] If the adhesive material is photocurable, the step of curing the adhesive material can comprise irradiation. If the adhesive material is heat-curable, the step of curing the adhesive material can comprise applying a heat source to the line pattern for heating the line pattern to a temperature above the curing temperature, in addition to the adhesive material under the bridge members. In the latter case, the step of curing the adhesive material can further comprise dissipating heat from the bridge members or actively cooling the bridge members.

[0023] The highly conductive material can be selected from, but is not limited to, copper, copper alloys (e.g. brass), aluminum and conductive fabric. The phrase "conductive fabric" as used in the present application shall in particular encompass a fabric having a continuous layer of conductive material attached to and covering at least a major portion of at least one surface. The continuous layer of conductive material can be attached to the at least one surface by applying a physical vapor deposition (PVD) method (e.g. evaporation or sputtering) or can be galvanically attached by electroplating. The electrical resistance of the continuous layer of conductive material attached to e.g. a surface of a fabric can be adjusted by selecting the type of fabric, the material used for the conductive material and the area weight of the applied conductive material. This design freedom can allow to cover any heating power requirements of e.g. steering wheel heater devices and a wide range of other automotive electric heating device applications (e.g. vehicle armrests, door or dashboard heaters etc.).

[0024] The scope of the present application also includes that the proposed method of manufacturing an electric heating device can be used in the field of building technology or printed circuit board (PCB) manufacturing technology, with the advantage that the etching process is omitted, which can make the PCB manufacturing more environmentally friendly.

[0025] In a preferred embodiment, wherein the predetermined line pattern comprises at least two conductive lines, and the method further comprises the subsequent steps of depositing a curable resist ink at a plurality of predetermined positions to be in electrical contact with the at least two conductive lines, and curing the attached resist ink to obtain a resist line.

[0026] This embodiment of the method allows to manufacture an electric heating device having a plurality of electric heating members based on the obtained series connection of resist lines, and wherein the electric feed line is made of a sheet of highly conductive material, thereby exhibiting superior capabilities to carry high current densities.

[0027] Preferably, the step of depositing a curable resist ink comprises applying a screen printing or inkjet printing process. The application of these high precision, cost effective manufacturing methods can facilitate low manufacturing tolerances, in particular with respect to dimensions in a direction perpendicular to the surface of the planar flexible carrier, which can enable uniform heating and high reliability of the plurality of electric heating members.

[0028] In a preferred embodiment, the method further comprises the subsequent step of depositing a continuous dielectric protective layer as a top layer, the top layer covering the one or more conductive lines and, where applicable, the resist line. In this way, an electric heating device having high reliability and long lifetime can be manufactured.

[0029] Preferably, the step of cutting through each bridge member at all end portions comprises applying a kiss cut process or a laser cutting process. Thereby, the cutting step can be performed in an efficient and reliable manner.

[0030] In a preferred embodiment of the method, the step of cutting through the sheet to obtain the predetermined line pattern comprises obtaining a subset of bridge members, the subset interconnecting portions of the at least one conductive line or another bridge member from an external direction. In this way, the handling properties of the predetermined line pattern obtained after the step of cutting through the sheet can be further improved.

[0031] In another aspect of the application, a pre-stage structure of an electric heating device, in particular for automotive applications, is provided. The pre-stage structure of the electric heating device comprises a dielectric planar flexible carrier and a predetermined line pattern. The predetermined line pattern comprises at least one electrically conductive line and a plurality of electrically conductive bridge members interconnecting portions of the at least one electrically conductive line. Only the at least one or more electrically conductive lines are fixedly attached to a surface of the flexible carrier by a layer of adhesive material.

[0032] The proposed electric heating device can have an excellent capability of carrying high current densities in the electrically conductive lines designed as electric feed lines forming part of the predetermined line pattern. The pre-stage structure of the proposed electric heating device can be easily transformed into an operable state by cutting through both end portions of each bridge member and removing the cut bridge members.

[0033] The electrically conductive lines designed as electric feed lines can be used to connect end portions of the at least one electrically conductive line designed as electrically resistive lines (in the following also simply referred to as resistive lines) for use as heating members.

[0034] Preferably, the predetermined line pattern has a thickness in the range between 5 pm and 100 pm. Thereby, the capability of carrying high current densities in the electrically conductive lines designed as electric feed lines can be realized, which allows covering most of the requirements from automotive applications.

[0035] In a preferred embodiment of the pre-stage structure of the electric heating device, the predetermined line pattern comprises a plurality of electrically conductive lines and a plurality of electrically resistive lines electrically connected in parallel through the plurality of electrically conductive lines. Thereby, the excellent capability of carrying high current densities in the electrically conductive lines designed as electric feed lines can be advantageously combined with uniform heating properties due to the plurality of electrically resistive lines.

[0036] Preferably, the one or more electrically resistive lines comprise at least one of the following: carbon black, graphite, graphene, an electrically conductive fabric or a material having a positive temperature coefficient resistivity. In this way, an effective heating function of the one or more electrically resistive lines can be ensured. If a material having a positive temperature coefficient resistivity is employed, the one or more electrically resistive lines can be laid out to be self-limiting.

[0037] In a preferred embodiment of the structure in the early stage of the electric heating device, the flexible carrier is formed by a foil, which is mostly made of a plastic material selected from the group of plastic materials formed by polyethylene terephthalate (PET), polyimide (PI), polyetherimide (PEI), polyethylene naphthalate (PEN), polyoxymethylene (POM), polyamide (PA), polyphthalamide (PPA), polyether ether ketone (PEEK), thermoplastic polyurethane (TPU) and combinations of at least two of these plastic materials.

[0038] The term "mostly" used in this application shall be particularly understood as a volume equal to or greater than 50%, more preferably greater than 70% and most preferably greater than 80% and shall encompass a portion of 100%, i.e. the planar flexible carrier foil is completely made of the selected plastic material or plastic materials, respectively.

[0039] These plastic materials can allow for an easy manufacturing and can provide a durable, cost-effective electrically insulating sheet as a base for the planar flexible carrier foil with low manufacturing tolerances.

[0040] Preferably, the planar flexible carrier is stretchable and the predetermined line pattern comprises a stretchable conductive fabric. The term "stretchable" used in this application shall be understood such that the planar flexible carrier can be stretched by an amount between 1% and 3%, preferably up to 4% and most preferably up to 5% of the mechanically unloaded extension length by an operator during installation or by a user of the electric heating device (e.g. a vehicle seat occupant). By employing a stretchable planar flexible carrier foil, the flexible electric heating device can be particularly advantageously used in applications with large surface curvatures, such as vehicle steering wheels. In such applications, the at least one electric heating member can be installed in a way that it highly adapts to the surface profile of the object to be heated (3D integration) and a good heat transfer of the object can be achieved. Conductive fabric materials are available in a large variability and there is a lot of experience regarding mechanical properties and manufacturing methods. Thus, the appropriate material can be chosen from a large pool to meet existing application requirements.

[0041] These and other aspects of the present application will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0042] It should be noted that features and steps, which have been individually described in the foregoing description, can be combined in any technically meaningful manner with each other and show further embodiments of the present application. The description is particularly characterized and detailed in connection with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0043] Further details and advantages of the present application will become apparent from the following detailed description of non-limiting embodiments with reference to the drawings, in which:

[0044] Figure 1 The steps of a method for manufacturing an electric heating device according to the present invention are shown in a side sectional view, and

[0045] Figure 2 The details of the early stage structure of the electric heating device according to the invention are schematically shown in a plan view. Detailed Implementation

[0046] Figure 1 The steps of two possible embodiments of a method for manufacturing an electric heating device 10, 10' according to the present invention are shown, the electric heating device being intended for automotive applications, for example, for automatically heating the steering wheel of a vehicle immediately after startup in cold environmental conditions. Figure 2 The details of the early stage structure of the electric heating device 10 are schematically shown.

[0047] The initial stage structure of the electric heating device 10 includes a dielectric planar flexible carrier 12 formed of foil, which may be made mostly or entirely of polyethylene terephthalate (PET). In other embodiments, the flexible carrier 12 may also be stretchable and may be made, for example, of a 25 μm polyimide foil. With a width of 40 mm, such a polyimide foil can be stretched by 5% by applying a force of approximately 90 N.

[0048] The preliminary stage structure of the electric heating device 10 also includes a predetermined line pattern 16. The predetermined line pattern 16 includes a conductive line 22 serving as an electric heating element and at least two highly conductive feed lines 18, 20 (hereinafter also simply referred to as feed lines) designed to be electrically connected to the ends of the conductive line 22. Furthermore, the preliminary stage structure of the electric heating device 10 includes a plurality of conductive bridge members 24, 26, through which portions of the conductive lines 22 are interconnected. A subset 26 of the plurality of bridge members 24, 26 interconnects portions of other bridge members 24 from an external direction (i.e., in a frame-like manner).

[0049] exist Figure 2 In the diagram, two highly conductive feed lines 18 and 20 are shown as wavy lines arranged along the longer side of the flexible carrier 12. A conductive line 22 is made continuous between the feed lines 18 and 20, such that each feed line 18 and 20 is connected to an adjacent portion of the conductive line 22, and portions of the conductive line 22 are alternately connected, thus forming a meander (not shown). The conductive line 22 has a much smaller width than the feed lines 18 and 20. Figure 2 (Not drawn to scale) so that when the electric heating device 10 is energized, the heating effect is mainly produced in the conductive wire 22.

[0050] In the following text, reference will be made to Figure 1 and Figure 2Two possible embodiments of the method according to the invention are described. In one step 40 of the method, a sheet 14 of highly conductive material of appropriate thickness is provided. The sheet 14 can be formed of a copper sheet and its thickness can be in the range between 5 μm and 100 μm. In this particular embodiment, the copper sheet thickness is 40 μm.

[0051] In another step 42 of the method, the sheet 14 is cut through to obtain the predetermined line pattern 16. The cutting process can be performed by employing a die or by using a laser cutting process, for example. In a step 44 of the method, which can be performed in parallel or subsequently, a dielectric planar flexible stretchable carrier 12 is provided, which is formed of a rectangular shaped 25 μm polyimide foil. In a next step 46, a layer of curable adhesive material 28 is deposited onto the surface of the flexible carrier 12. The adhesive material 28 can be applied by a coating or printing process, for example, or can be applied by distributing the adhesive as a powder.

[0052] In a further step 48, the predetermined line pattern 16 is placed on the layer of adhesive material 28. The presence of the plurality of bridge members 24, 26 Figure 2 ) will greatly facilitate, if not make possible, step 48. Then, in a next step 50 Figure 1 ), the adhesive material 28 under the line pattern 16 is cured, except for the adhesive material 28 under the bridge members 24, 26. To this end, the line pattern 16 can be heated to a temperature above the curing temperature of the adhesive material 28, except for the bridge members 24, 26, or the adhesive material 28 under the line pattern 16 can be irradiated, except for the bridge members 24, 26, depending on the type of adhesive material 28. After this step 50, which completes the pre-stage structure of the electrical heating device 10, the line pattern 16 is fixedly attached to the flexible carrier 12, except for the bridge members 24, 26, which are loosely positioned on the adhesive material 28.

[0053] The pre-stage structure can be processed in two further steps 52, 54 to obtain the completed electrical heating device 10. In one of the steps 52, each bridge member 24, 26 is cut through at all ends between the portions of the conductive lines 22 and the feed lines 18, 20 that are interconnected by the respective bridge member 24, 26. This step 52 can include the application of a kiss-cut process or a laser cutting process. In a further step 54, the cut bridge members 24, 26 are removed.

[0054] In principle, the electrical heating device 10 is completed at this stage. In order to better protect against external influences and to increase reliability and lifetime, an additional subsequent step 56 can be carried out, namely depositing a continuous dielectric protective layer 30 as a top layer covering the electrically conductive lines 22 and the feed lines 18, 20. As a material for the protective layer 30, for example, an acrylic adhesive, a rubber or a polyurethane can be used, but other materials can also be used which appear suitable to the person skilled in the art.

[0055] In an alternative embodiment of the pre-stage structure of the electrical heating device 10', only one wave-shaped electrically conductive line 22 is arranged between the two highly conductive feed lines 18, 20 instead of forming six sections of the flow path, the electrically conductive line 22 also serving as a feed line (return line) and extending parallel to the side edges of the flexible carrier 12.

[0056] The alternative embodiment of the pre-stage structure of the electrical heating device 10' also comprises a plurality of electrically conductive lines designed as electrically conductive heater lines and connected in parallel by the two feed lines 18, 20 and the return line 22. The electrically conductive heater lines comprise a carbon black material, which has an electrical resistivity with a positive temperature coefficient (PTC).

[0057] In order to manufacture the alternative embodiment of the pre-stage structure of the electrical heating device 10', the method also comprises a step carried out after the step 54 of removing the cut bridge members 24, 26.

[0058] In one of these steps 58, a curable resistive ink 32 is deposited at a plurality of predetermined locations to be in electrical contact with at least two electrically conductive lines 18, 20, 22, i.e. with one of the two feed lines 18, 20 and the return line 22. The step 58 of depositing the curable resistive ink 32 can be carried out by applying a screen printing or an inkjet printing process.

[0059] This step 58 is followed by a step 60 of curing the attached resistive ink 32 to obtain electrically conductive heater lines. An additional subsequent step 56 can be carried out, namely depositing a continuous dielectric protective layer 30 as a top layer covering the electrically conductive lines 18, 20, 22 and the electrically conductive heater lines.

[0060] While the application has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the application is not limited to the disclosed embodiments.

[0061] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality, meaning at least one. The mere fact that measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0062] List of reference signs

[0063] 10 electric heating device

[0064] 12 dielectric planar flexible carrier

[0065] 14 sheet of highly conductive material

[0066] 16 predetermined line pattern

[0067] 18 highly conductive feed line

[0068] 20 highly conductive feed line

[0069] 22 conductive line

[0070] 24 conductive bridge member

[0071] 26 conductive bridge member

[0072] 28 adhesive material

[0073] 30 dielectric protective layer

[0074] 32 resistive ink

[0075] Method steps:

[0076] 40 providing a sheet of highly conductive material

[0077] 42 cutting through the sheet to obtain a predetermined line pattern

[0078] 44 providing a dielectric planar flexible and stretchable carrier

[0079] 46 depositing an adhesive material onto the surface of the flexible carrier

[0080] 48 placing the predetermined line pattern on the adhesive material layer

[0081] 50 curing the adhesive material except for the material under the bridge members

[0082] 52 cutting through all bridge member ends

[0083] 54 removing the cut bridge members

[0084] 56 depositing a dielectric protective layer

[0085] 58 depositing a resistive ink

[0086] 60 curing the resistive ink

Claims

1. A method of manufacturing an electric heating device (10), the method comprising at least the steps of: (40) providing a sheet (14) of electrically conductive material of predetermined thickness, (42): cutting through the sheet (14) to obtain a predetermined line pattern (16) comprising at least one electrically conductive line (18, 20, 22), wherein electrically conductive bridge members (24, 26) interconnecting different portions of the at least one electrically conductive line (18, 20, 22), (44) providing a dielectric planar flexible carrier (12), (46) depositing a layer of curable adhesive material (28) onto a surface of the flexible carrier (12), (48) placing the obtained line pattern (16) onto the layer of adhesive material (28), (50) curing the adhesive material (28) under the line pattern (16) except for the adhesive material (28) under the bridge members (24, 26), (52) cutting through each bridge member (24, 26) at all ends between different portions of the at least one electrically conductive line (18, 20, 22) interconnected by the respective bridge member (24, 26), and (54) removing the cut bridge members (24, 26).

2. The method of claim 1, wherein, The predetermined line pattern (16) comprises at least two electrically conductive lines (18, 20, 22), and the method further comprises the subsequent step (58) of depositing a curable resistive ink (32) at a plurality of predetermined locations to be in electrical contact with the at least two electrically conductive lines (18, 20, 22), and the subsequent step (60) of curing the attached resistive ink (32) to obtain a resistive line.

3. The method of claim 2, wherein, The step (58) of depositing a curable resistive ink (32) comprises applying a screen printing or inkjet printing process.

4. The method according to any one of claims 2-3, further comprising the subsequent step (56) of depositing a continuous dielectric protective layer (30) as a top layer covering one or more of the electrically conductive lines (18, 20, 22) and, where applicable, the resistive line.

5. The method of any of claims 1-3, wherein, The step (52) of cutting through each bridge member at all ends comprises applying a kiss-cutting process or a laser cutting process.

6. The method of any of claims 1-3, wherein, The step (42) of cutting through the sheet (14) to obtain a predetermined line pattern (16) comprises obtaining a subset of the bridge members (26) interconnecting different portions of the at least one electrically conductive line (18, 20, 22) from an external direction or other bridge members (24).

7. The method of claim 1 or 2, wherein, The electric heating device (10) is for automotive applications.

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