HYBRID PRINTED HEATER WITH OPTIONAL PTC EFFECT

Abstract

A method of producing an electric heating device, in particular for automotive application, includes steps of: cutting through a sheet of electrically highly conductive material of appropriate thickness for obtaining a predetermined line pattern having at least one electrically conductive line with electrically conductive bridge members interconnecting portions of the at least one electrically conductive line; depositing a layer of curable adhesive material onto a surface of a dielectric, planar, flexible carrier; placing the obtained line pattern onto the layer of adhesive material; curing the adhesive material below the line pattern with the exception of the adhesive material below the bridge members; 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 removing the cut bridge members.

Claims

1. A method of producing an electric heating device for automotive application, including at least the following steps: providing a sheet of electrically highly conductive material of appropriate thickness, obtaining a predetermined line pattern by cutting through the sheet, the predetermined line pattern comprising at least one electrically conductive line with electrically conductive bridge members interconnecting portions of the at least one electrically conductive line, providing a dielectric, planar, flexible carrier, depositing a layer of curable adhesive material onto a surface of the flexible carrier, placing the obtained line pattern onto the layer of adhesive material, curing the adhesive material below the line pattern with the exception of the adhesive material below the bridge members, 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 removing the cut bridge members.

2. The method as claimed in claim 1, wherein the predetermined line pattern includes at least two electrically conductive lines, and the method further comprises subsequent steps of depositing curable electrically resistive ink at a plurality of predetermined locations to be in electric contact with the at least two electrically conductive lines and of curing the attached electric resistive ink for obtaining electrically resistive lines.

3. The method as claimed in claim 2, wherein the step of depositing curable electrically resistive ink includes applying a screen printing or an ink jet printing process.

4. The method as claimed in claim 1, further comprising a subsequent step of depositing a continuous dielectric protection layer as a top layer, covering the electrically conductive line or lines and, if applicable, the electrically resistive lines.

5. The method as claimed in claim 1, wherein the step of cutting through each bridge member at all ends comprises applying a kisscut process or a laser cutting process.

6. The method as claimed in claim 1 wherein the step of cutting through the sheet for obtaining a predetermined line pattern includes obtaining a subset of the bridge members that interconnect portions of the at least one electrically conductive line or other bridge members from an outside direction.

7. A pre-stage of an electric heating device for automotive application, comprising: a dielectric, planar, flexible carrier, and a predetermined line pattern including at least one electrically conductive line, and a plurality of electrically conductive bridge members interconnecting portions of at least one electrically conductive line, wherein only the at least one electrically conductive line is fixedly attached to a surface of the flexible carrier by a layer of adhesive material.

8. The pre-stage of the electric heating device as claimed in claim 7, wherein the predetermined line pattern has a thickness between 5 μm and 100 μm.

9. The pre-stage of the electric heating device as claimed in claim 7, wherein the predetermined line pattern includes a plurality of electrically conductive lines and a plurality of electrically resistive lines that are electrically connected in parallel by the plurality of electrically conductive lines.

10. The pre-stage of the electric heating device as claimed in claim 7, wherein the electrically resistive line comprises or the electrically resistive lines comprise at least one out of carbon black, graphite, graphene, an electrically conductive textile or a material that has an electrical resistivity with a positive temperature coefficient.

11. The pre-stage of the electric heating device as claimed in claim 7 wherein the flexible carrier is formed by a foil that is made for the most part from a plastic material that is selected from a group of plastic materials consisting of: 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.

12. The pre-stage of the electric heating device as claimed in claim 7, wherein the flexible carrier is stretchable, and the predetermined line pattern comprises stretchable electrically conductive textile.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:

[0037] FIG. 1 illustrates steps of a method in accordance with the invention of producing an electric heating device in a sectional side view, and

[0038] FIG. 2 schematically shows a detail of a pre-stage of an electric heating device in accordance with the invention in a plan view.

DETAILED DESCRIPTION

[0039] FIG. 1 illustrates steps of two possible embodiments of a method in accordance with the invention of producing an electric heating device 10, 10′ which is intended to be used in an automotive application, for instance for automatically heating a vehicle steering wheel right after start-up at cold ambient conditions. A detail of a pre-stage of the electric heating device 10 is schematically shown in FIG. 2.

[0040] The pre-stage of the electric heating device 10 comprises a dielectric, planar, flexible carrier 12, formed by a foil, which can be made for the most part or completely from polyethylene terephthalate (PET). In other embodiments, the flexible carrier 12 can also be stretchable and can for instance be made from a 25 μm polyimide foil. With a width of 40 mm, such polyimide foil can be stretched by an amount of 5% by applying a force of about 90 N.

[0041] The pre-stage of the electric heating device 10 further includes a predetermined line pattern 16. The predetermined line pattern 16 comprises an electrically conductive line 22 to serve as an electric heating member and at least two electrically conductive lines designed as electrically highly conductive feed lines 18, 20 (in the following also briefly referred to as feed lines) that are electrically connected to ends of the electrically conductive line 22. Further, the pre-stage of the electric heating device 10 includes a plurality of electrically conductive bridge members 24, 26 by which portions of the electrically conductive line 22 are interconnected. A subset 26 of the plurality of bridge members 24, 26 interconnect portions of other bridge members 24 from an outside direction, i.e. in a frame-like manner.

[0042] In FIG. 2, the two electrically highly conductive feed lines 18, 20 are shown as undulated lines disposed along longer side edges of the flexible carrier 12. The electrically conductive line 22 arranged between the feed lines 18, 20 is continued such that each feed line 18, 20 is connected to the adjacent portion of the electrically conductive line 22, and the portions of the electrically conductive line 22 are alternately connected so as to form a meander (not shown). The electrically conductive line 22 has a much smaller width than the feed lines 18, 20 (FIG. 2 is not to scale) to generate a heating effect mainly in the electrically conductive line 22 when the electric heating device 10 is energized.

[0043] In the following, two possible embodiments of the method in accordance with the invention will be described with reference to FIGS. 1 and 2. In one step 40 of the method, a sheet 14 of electrically highly conductive material of appropriate thickness is provided. The sheet 14 can be formed by a copper sheet, and its thickness can range between 5 μm and 100 μm. In this specific embodiment, the copper sheet thickness is 40 μm.

[0044] In another step 42 of the method, the sheet 14 is cut through for obtaining the predetermined line pattern 16. The cutting process can for instance be performed by employing a die or by using a laser cutting process. In a step 44 of the method that can be carried out in parallel or subsequently, a dielectric, planar, flexible and stretchable carrier 12, which is formed by a 25 μm polyimide foil of rectangular shape, is provided. In a next step 46, a layer of curable adhesive material 28 is deposited onto a surface of the flexible carrier 12. The adhesive material 28 can for instance be applied by a coating or printing process or by distributing the adhesive as powder.

[0045] The predetermined line pattern 16 is placed onto the layer of adhesive material 28 in another step 48. This step 48 is greatly facilitated or even made possible by the presence of the plurality of bridge members 24, 26 (FIG. 2). In the next step 50 then (FIG. 1), the adhesive material 28 below the line pattern 16 is cured with the exception of the adhesive material 28 below the bridge members 24, 26. To this end, the line pattern 16 except for the bridge members 24, 26 can be heated up to a temperature above the curing temperature of the adhesive material 28, or the adhesive material 28 below the line pattern 16 except for the bridge members 24, 26 can be illuminated, depending on the type of adhesive material 28. After this step 50, which completes the pre-stage of the electric heating device 10, the line pattern 16 is fixedly attached to the flexible carrier 12 with the exception of the bridge members 24, 26, which lie loosely on the adhesive material 28.

[0046] The pre-stage can be made in two more steps 52, 54 to the finished electric heating device 10. In one of the steps 52, each bridge member 24, 26 is cut through at all ends between portions of the electrically conductive lines 22 and the feed lines 18, 20 interconnected by the respective bridge member 24, 26. This step 52 can include applying a kisscut-process or a laser cutting process. In the other step 54, the cut bridge members 24, 26 are removed.

[0047] In principle, the electric heating device 10 is finished at this stage. For better protection against outer influences and for improving reliability and lifetime, an additional, subsequent step 56 of depositing a continuous dielectric protection layer 30 as a top layer, covering the electrically conductive line lines 22 and the feed lines 18, 20, can be carried out. As a material for the protection layer 30, for instance acrylic adhesive, rubber or polyurethane can be employed, but also other materials that appear to be suitable to those skilled in the art can be used.

[0048] In an alternative embodiment of the pre-stage of the electric heating device 10′, only one undulated electrically conductive line 22 instead of six portions forming a meander is arranged between the two electrically highly conductive feed lines 18, 20, which also serves as a feed line (return line) and is running parallel to the side edges of the flexible carrier 12.

[0049] The alternative embodiment of the pre-stage of the electric heating device 10′ further includes a plurality of electrically conductive lines that are designed as electrically conductive heater lines and are 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 having an electrical resistivity with a positive temperature coefficient (PTC).

[0050] For producing the alternative embodiment of the pre-stage of the electric heating device 10′, the method further comprises steps to be carried out after the step 54 of removing the cut bridge members 24, 26.

[0051] In one 58 of these steps, curable electrically resistive ink 32 is deposited at a plurality of predetermined locations to be in electric contact with at least two electrically conductive lines 18, 20, 22, i.e. with one of the two feed lines 18, 20 and with the return line 22. The step 58 of depositing curable electrically resistive ink 32 can be executed by applying a screen printing or an ink jet printing process.

[0052] This step 58 is followed by a step 60 of curing the attached electric resistive ink 32 for obtaining the electrically conductive heater lines. An additional, subsequent step 56 of depositing a continuous dielectric protection layer 30 as a top layer, covering the electrically conductive lines 18, 20, 22 as well as the electrically conductive heater lines can be carried out.

[0053] While embodiments of the invention have 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 invention is not limited to the disclosed embodiments.

[0054] Other variations to be 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, which is meant to express a quantity of at least two. The mere fact that certain 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 scope.