Method for manufacturing a heat-generating element

Abstract

Method for producing a heat-generating element (18) in which at least two electrical conductor elements (6) provided with perforations are placed on a film (4) covered with an adhesive mass (5) and pressed against the film (4) in such a way that the mass (5) is forced into the perforations, followed by placing at least one PTC element (14) on one of the conductor elements (6a) and then placing the other of the conductor elements (6b) together with the film (4) adhering to it on the PTC element (14) opposite one of the conductor elements (6a).

Description

[0001] The present invention relates to a method for producing a heat-generating element of an electric heating device. In particular, the present invention aims to specify the production of a heat-generating element of an electric auxiliary heater of a motor vehicle and such a heat-generating element.

[0002] The present invention relates in particular to a method for producing a heat-generating element with a PTC element and conductor elements applied to both sides thereof, as well as an electrical insulation applied to the outside of the conductor elements.

[0003] Such a heat-generating element is known from EP 1 916 873 A1. This document discloses an embodiment in which the conductor element in the form of contact plates is coated on the outside with an insulating layer formed by a ceramic plate.

[0004] In the embodiment of EP 1 916 873 A1, the ceramic plate is connected together with the associated conductor element in the form of a contact plate by overmolding to a plastic frame.

[0005] EP 1 768 457 A1, EP 3 101 999 A1 and EP 2 873 296 B1 disclose other solutions in which the electrical insulation is glued in the form of a multi-layer insulation layer onto a contact sheet forming the conductor element.

[0006] DE 10 2017 223 785 A1 is prior art according to Section 3 (2) No. 1 of the German Patent Act (PatentG). It discloses a method in which a shielding foil is partially covered with an electrically insulating layer. Two conductor elements, one of which is connected to a PTC element, are placed on the electrically insulating layer and connected to it. The shielding foil is folded in such a way that a layer is formed from the PTC element and the conductor tracks adjacent to it on both sides. Finally, the foil is folded in such a way that a free end of the foil, including the layer, is placed from the outside against a section of the shielding foil surrounding the layer and connected to it. This creates an overlap region that lies on a main lateral surface of the PTC element.

[0007] US 6 084 206 A discloses a thermal blanket comprising an outer layer of protective glass fiber foam which ensures the safety of the operator, a layer of closed-cell silicone foam which provides thermal and electrical insulation, a layer of thermally conductive mesh, a further layer of thermally conductive silicone with cut holes, the holes containing positive temperature coefficient (PTC) heating elements, a further layer of conductive mesh, a layer of thermally conductive silicone and an inner layer of moderately conductive, cured silicone or foam.

[0008] Such a design offers the advantage that the contact plate and insulation are joined together to form a single unit, meaning only this unit needs to be handled and installed in a positioning frame. However, this results in a multi-layered structure from the PTC element to the outer surface that dissipates the heat. Each individual layer must be penetrated by the heat to be dissipated to the outside. Conductive disturbances for the heat to be dissipated to the outside can occur at each layer. Such resistances reduce efficiency because, due to its self-regulating properties, the PTC element does not absorb any power current when overheated. This reduces the efficiency of the PTC element.

[0009] The present invention is based on the problem of providing a simple and therefore economical method for producing a heat-generating element. The heat-generating element according to the invention should be easy to manufacture and allow for good heat dissipation of the heat generated by the PTC element to the outside.

[0010] To solve the procedural problem, the present invention proposes a method having the features of claim 1.

[0011] In this process, electrical conductor elements are applied to a foil coated with an adhesive compound. These electrical conductor elements are placed on the foil at a distance from one another. The electrical conductor elements serve to supply current to a PTC element with different polarities. The adhesive compound is applied to the side of the foil on which the conductor elements are applied. Thus, after the conductor elements are applied, a certain degree of adhesion is created between the conductor elements and the foil, which is mediated by the adhesive compound. According to the invention, the conductor elements are provided with perforations. They are electrical conductor elements.

[0012] The conductor elements are preferably pressed against the foil in such a way that the compound is forced into the openings. This creates intimate contact between the compound and the conductor elements, so that they are already solidly connected to the foil after being pressed against the foil.

[0013] Subsequently, at least one PTC element is placed on one of the conductor elements. The other of the conductor elements, along with the foil attached to it, is then placed on the PTC element opposite the first of the conductor elements.

[0014] The PTC element is typically metallized on opposing main surfaces. This metallization serves to conduct the power current across the entire surface of the PTC element.

[0015] This results in a layered structure in which the foil forms the outer surface of each heat-generating element. The adhesive mass is located on the inner surface of the foil facing the PTC element. Due to the pressure applied, this mass is at least partially in the plane of the conductor element. The PTC element is located between the conductor elements.

[0016] The conductor element with perforations is typically an electrically conductive element formed as a braid, knitted fabric, perforated sheet, or expanded metal. In a plan view of the conductor element, i.e., a view perpendicular to the main side surface of the track-shaped conductor element, the element is typically at least partially transparent. Thus, the perforations typically extend completely through the conductor element in the vertical direction. The perforations are preferably provided on a sheet in a uniform pattern distributed over the entire surface of the conductor element adjacent to the PTC element.

[0017] A wire mesh within the meaning of the present invention is usually formed from braided wire material. In this case, a wire strand is placed alternately under and over further strands extending transversely to this wire strand. The wire strand adjacent to the wire strand is provided exactly offset therefrom, so that a woven fabric is produced with wire strands extending at right angles to it, which are each positively and / or non-positively connected to one another in order to form a stable woven fabric. The greatest height of the mesh is usually achieved at the turning points of the individual wire strands, i.e. at the positions where the wire strand is in contact with a wire strand extending transversely thereto. This highest point determines the thickness of the wire mesh. The strands can also be welded.

[0018] This wire mesh can be made of a metallic wire or an electrically conductive wire made of another material, such as carbon. It is also possible to combine wire strands of different materials in the mesh or fabric to ensure the necessary integrity of the wire structure, sufficient electrical conduction, and ultimately the lowest possible weight. It is advantageous to make the wires thin. The wires should have a thickness of 0.15 mm (mesh 0.3 mm) to a maximum of 0.3 mm (mesh 0.6 mm). Compressing reduces the thickness by approximately 30-50% and increases rigidity. This allows for a larger aperture, saving costs and material. This allows for less adhesive to be used, which improves heat transfer. The thinner the wires, the lower the stability. The thicknesses stated above refer to a wire compressed by approximately 50%.The compression to increase strength can be between 30% and 50%. The wire mesh can be compressed using pressure. This results in greater stability and less deformability. The electrical and thermal contact resistances are improved.

[0019] The conductor element should preferably be designed such that it forms discrete support points on its inner surface adjacent to the PTC element, through which the conductor element is electrically connected to the PTC element. These support points project toward the PTC element, with essentially a surface overlap (fully or partially) between the conductor element and the PTC element or insulation. Such a more point-based contact is preferable with regard to the reliable introduction of the power current to the PTC element.

[0020] Particularly when the conductor element is made of perforated sheet metal or expanded metal, the terminal lugs projecting beyond the PTC element are usually formed directly into the conductor element as a single piece. Such terminal lugs serve to connect the heat-generating element. The terminal lugs are typically formed from sheet metal strips. The terminal lugs can be soldered, welded, or electrically bonded to a braid or knitted fabric forming the conductor element.

[0021] The compound is typically a compound with good thermal conductivity. The compound preferably has a thermal conductivity of at least 3 W / (m×K), particularly preferably at least 5 W / (m×K). The compound can be applied to the film using a technology used in the production of adhesive tapes, in which the film is passed over rollers through a bath consisting of the compound. To adjust the viscosity of the compound, it can be mixed with a solvent. The compound preferably used is a plastic compound which sets or cures completely or partially after the film has been coated with the compound. A crosslinking plastic is preferably used, although after the film has been coated, this can also cure or crosslink more quickly by adding heat and / or exposure to radiation.The device used usually has a heating or irradiation section through which the film coated with the mass passes.

[0022] In addition to the previously mentioned coating of the film, the mass can also be applied to the film by printing, calendering or spraying, whereby in the case of printing, doctoring is preferable.

[0023] The compound may contain a filler to adjust its thermal conductivity or electrical properties. The filler may be ceramic and / or metallic particles.

[0024] The mass may, for example, be a two-component silicone to which gasoline or toluene is added for dilution during production in order to obtain a viscosity in a range of between 4 and 15 Pa s, preferably between 5 and 8 Pa s, at 25°C.

[0025] The method according to the invention offers the advantage that by pressing the conductor elements onto the foil, they are positioned and secured. Once the two conductor elements are placed on the PTC element, the mass can also position the conductor elements relative to the PTC element.

[0026] The compound can have a relatively high filler content, which is formed from particles of an electrically insulating material. A material with good thermal conductivity is preferably used, such as aluminum oxide. The filler content should be at least 50 vol.%, particularly preferably between 75 vol.% and 95 vol.%. The filler particles must be designed to fit the openings so that the filler particles cannot block the openings within the conductor element when the compound is pressed through it. The filler particles should have a diameter that does not exceed 10% of the equivalent diameter of the openings. While the filler content improves the thermal conductivity of the compound, a high filler content also impairs the flowability of the compound and thus hinders the penetration of the compound into the openings of the conductor element.A lower filler content is therefore advantageous for a conductor element with a small aperture. A relatively solid conductor element with only a few and / or small openings for admitting the mass into the plane of the conductor element also allows for good thermal conductivity within the plane containing the conductor element due to its solidity. Thus, in a relatively solid conductor element, the filler content can be low or even completely absent.

[0027] For this purpose, according to a preferred development of the present invention, the mass is pushed through the conductor element when it is pressed on, so that the mass is provided on the side of the conductor element opposite the foil. Both conductor elements can undergo this treatment. Alternatively, only the conductor element onto which the PTC element is placed can be pressed on in the manner described above. The mass should be pressed through the conductor element in such a way that the mass does not protrude, or only slightly protrudes, above the plane of the support points. When the PTC element is placed on, it should be electrically conductively connected to the conductor element, if necessary after applying a certain contact pressure. The mass is pushed back into the openings by the pressed-on PTC element.The PTC element is bonded to the corresponding conductor element and the foil, so that only a few parts have to be handled during production.

[0028] The mass should fill the openings as completely as possible so that no cavities or blowholes remain in the plane of the heat-generating element defined by the conductor element, which improves the coupling of the heat generated by the PTC element.

[0029] The method according to the invention can be carried out using two pieces of foil, each of the pieces of foil being connected to one of the conductor elements. To further simplify the method according to the invention, it is proposed to place the at least two conductor elements one behind the other on a continuous foil. In this method, the other of the conductor elements is placed onto the PTC element by folding the foil over. The foil is preferably folded over using a rod which is placed against the PTC element at its end, has approximately the same thickness as the PTC element (extension in the vertical direction), and is enclosed by the foil when it is folded over. The rod is then located between the fold in the foil and the PTC element.For example, the rod has a semicircular cross-sectional shape, with the foil extending around the convex circumferential section of the rod and the straight circumferential section of the rod resting against an end face of the PTC element.

[0030] In the method according to the invention, it should be ensured that after the conductor elements have been placed on the foil, the ground is pressed as far as possible through the conductor elements by pressing the conductor elements against the foil, so that the ground on both conductor elements is also provided on the inner surface of the conductor elements opposite the foil. After the other of the two conductor elements has been placed on the PTC element, the ground is accordingly located immediately adjacent to and / or in contact with the PTC element. These variants are conceivable, for example, at a single interface between the conductor element and the PTC element. This is because the conductor element is usually planar orThe ground contacts the PTC element over its entire surface, and it is conceivable that in certain surface areas the ground extends above the plane of the conductor element before the PTC element is applied, whereas in other surface areas of the conductor element the ground is positioned at the same height as the surface of the conductor element facing the PTC element or remains lower than this inner surface of the conductor element. For a conductor element provided with support points, a full-surface contact means that all support points provided over the entire surface of the conductor element are in contact with the contact surface of the PTC element.

[0031] After applying the other of the conductor elements, a layered structure consisting of the foil layers with the compound, the conductor elements, and the PTC element provided between them should preferably be pressed together. This ensures that the conductor elements are electrically connected to the PTC element over their entire surface. Furthermore, the flow of the compound in the plane of the conductor element should fill any voids and defects with the compound. This results in a good thermally conductive connection between the PTC element and the outer surface of the foil. The foil forms the outer surface of the finished product. A heat-emitting element, such as a corrugated fin element of an air heater, can be applied to this foil to transfer the heat generated by the PTC element to the air to be heated. The heat-generating element manufactured in the manner described above can equally well be inserted into a U-shaped pocket of a water heater.

[0032] With regard to the positioning of the connection lugs or the positioning of the heat-generating element in an electric heating device used in a motor vehicle, the aforementioned layered structure is preferably located in a frame-shaped housing made of an insulating material, for example plastic. The connection lugs usually protrude beyond the housing. The housing has a housing opening which is adapted to accommodate the aforementioned layered structure. The layered structure is usually only pressed into the housing after it has been inserted. Mass pressed laterally over the PTC element can fill gaps between the frame-shaped housing and the layered structure, thereby improving the heat extraction from the PTC element and / or achieving an adhesive connection between the housing and the layered structure.Examples of such frame-shaped housings are described in EP 1 768 457 A1 or EP 2 637 474 A1. To avoid electrical arcing and voltage carryover, the conductor elements usually have a base area that is smaller than the opposite main side surface of the PTC element against which the conductor element rests. The conductor element can offset inwards by 1 to 5 mm compared to the outer circumferential surface of the PTC element. The foil, however, is larger than the conductor element and projects completely beyond the conductor element. The foil is usually also larger than the PTC element. The foil therefore usually projects completely beyond the base area of ​​the PTC element. This also applies to the wrap, for which purpose it is folded around the rod. Such a layered structure is usually only projected laterally by the connection lugs.The connection lugs to the conductor elements, which each supply current to the PTC element with different polarity, usually protrude beyond the layer structure at one end, which enables the electrical connection to the heat-generating element.

[0033] According to a preferred embodiment of the present invention, the compound is a plastic compound that is applied flatly to the film and adjusted to a Shore A hardness of between 25 and 40 for the application of the conductor elements. The film has a thickness of between 50 µm and 100 µm. The layer density of the compound is typically between 200 µm and 350 µm.

[0034] This hardness allows the conductor elements to be easily pressed into the mass.

[0035] According to a preferred embodiment of the present invention, the compound is a crosslinking plastic compound. The compound is pre-crosslinked before the sheet metal elements are applied. In the pre-crosslinked state, the compound typically has the aforementioned hardness values. The degree of crosslinking of the compound is between 40 and 70%. The final crosslinked compound has a Shore A hardness of > 70. This final crosslinking is typically achieved at the end of the heat-generating element's production and not only after continuous operation of the heat-generating element in an electric heating device.

[0036] According to a further preferred embodiment of the present invention, after the other of the conductor elements has been applied, the compound is finally crosslinked together with the adhering foil by applying external pressure and an elevated temperature. The pressure should be between 2 and 3.5 N / mm 2The elevated temperature should be between 100°C and 200°C. This pressure can be so high that the mass is displaced into the plane occupied by the PTC element and this mass completely surrounds the PTC element. In this way, the PTC element is absorbed by the mass. Only the connection lugs protrude through the mass and beyond the foil. The heat-generating element can comprise, in a manner known per se, a positioning frame which holds several PTC elements in a predetermined position, as is known from EP 1 768 457 A1 or EP 2 873 296 B1. Such a positioning frame can cover and seal the PTC elements at the edges, as is already known from this prior art.

[0037] In the element manufactured according to the method according to the invention, the mass is provided in the plane of at least one of the conductor elements, resulting in a good connection between the conductor element provided with a perforation and the insulation. Furthermore, the outer surface of the heat-generating element is shifted toward the PTC element, thus reducing the heat conduction path while maintaining good insulation.

[0038] With this element, the PTC element adheres preferentially to the conductor element through the ground, thus easily creating a permanent bond between the PTC element and the insulation. Typically, only the conductor element itself and the ground are located in the plane of the conductor element. This ensures good thermal conductivity.

[0039] The heat-generating element can also be provided with EMC protection, for example, by being covered with an electrically conductive foil. Edge areas of the heat-generating element can also be overmolded for sealing and sealing.

[0040] Further details and advantages of the present invention will become apparent from the following exemplary embodiment of the invention with the accompanying drawings. In these drawings: Fig. 1 a perspective view of a wire mesh as an embodiment of an electrical conductor element provided with perforations; Fig. 2a to 2d are plan views of various method steps in carrying out an embodiment of the method according to the invention and Fig. 3a to 3d Longitudinal sectional views of different phases of the embodiment.

[0041] The Fig. Figure 1 shows a perspective view of a wire mesh 1 with a plurality of interwoven wire strands 2. The wire strands 2 extend at right angles to each other and are alternately threaded over and under each other, forming the mesh in the conventional manner.

[0042] At the intersection points of the wire strands, upper and lower discrete support points are formed, with which the wire mesh, which represents an embodiment of an electrical conductor element provided with perforations, rests pointwise but also flatly on the opposite layers of a layer structure to be described below.

[0043] The Fig. 2 shows a plan view of a film provided with a mass; the Fig. 3a shows a corresponding longitudinal sectional view of an enlarged detail of the film with the compound, where the film is identified by reference numeral 4 and the compound by reference numeral 5. This film is cut from a supply as a single length. The supply contains a film 4 previously coated with compound 5. The film 4 can be a polyimide film. The compound is a two-component silicone, which is provided with a thinner to achieve a relatively low viscosity. This makes compound 5 relatively flowable. Compound 5 is already partially crosslinked in the supplied starting material. It has a Shore A hardness of between 25 and 40.

[0044] As the Fig. 2b and Fig. 3b, electrical conductor elements 6 are placed on this mass 5. The electrical conductor elements 6 are identically shaped cut-outs of the Fig. 1. The foil 4 with the applied mass 5 is clearly wider than the conductor element. Thus, the foil 4 with the mass 5 projects beyond the conductor element 6 in the width direction on both sides. The foil 4 with the mass 5 also has a corresponding projection at the free end faces. There is a free space between the two conductor elements 6. The conductor elements 6 are spaced apart from each other.

[0045] How Fig. As shown in Figure 3b, the conductor element is not only placed on the mass 5, but is also pressed into the mass 5. The conductor element 6 is pressed into the mass 5 in such a way that discrete support points, designated by reference numeral 10, at the intersection points of the wire strands 2 are located at approximately the same height as the outer surface of the mass 5, designated by reference numeral 12.

[0046] The Fig. 2c and 3c respectively illustrate the embodiment after placing the PTC element, which is identified by reference numeral 14, on the right conductor element 6a. The base area of ​​the PTC element 14 is larger than the base area of ​​the conductor element without the terminal lugs 8. The size ratios are shown in Fig. 2c by dash-dotting the contour of the left conductor element 6a. Fig. 2c or 3c also illustrates a rod 16 made of an insulating material, which is placed at its end against the PTC element 14 and between the two conductor elements 6 on the ground 5.

[0047] In Fig. 2c shows the embodiment in a plan view after folding over the foil 4. The opposing foil sections 4 overlap. They form the outer surface of the heat-generating element designated by reference numeral 18, which is only projected beyond by the two connecting lugs 8. Fig. 2b The connecting lugs 8 provided offset from one another in the longitudinal direction have the same extension in the longitudinal direction of the heat-generating element 18, but are offset from one another in the width direction, whereby the air and creepage distance between the two connecting lugs 8, which serve to supply the heat-generating element 18 with the power current, is increased.

[0048] How Fig. 3d shows the other, in Fig. 2b and Fig. 2c right shows the conductor element 6b with its associated support points 10 against the surface of the PTC element 14.

[0049] As the sectional view after Fig. As illustrated in Figure 3d, the rod 16 rests with a straight outer peripheral section against the essentially straight end face of the PTC element 14. The rod 16 is semicircular. The convex area is enclosed by the film 4. List of reference symbols 1 wire mesh 2 stranded wires 4 slides 5 Mass 6 ladder element 8 connection lug 10 support point 12 outer surface of mass 5 14 PTC element 16 bars 18 heat-generating element

Claims

[1] Method for producing a heat-generating element (18), in which at least two electrical conductor elements (6) provided with perforations are placed on a film (4) provided with an adhesive mass (5) and at a distance from one another on the film (4) and pressed against the film (4) in such a way that the mass (5) is forced into the perforations, then at least one PTC element (14) is placed on one of the conductor elements (6a) and then the other of the conductor elements (6b) is placed together with the film (4) adhering thereto opposite to one of the conductor elements (6a) on the PTC element (14). [2] Method according to claim 1, characterized by that the mass (5) is pressed through the conductor element (6) when it is pressed on, so that the mass (5) is provided on the side of the conductor element (6) opposite the film (4). [3] Method according to claim 1 or 2, characterized bythat at least two conductor elements (6a; 6b) are placed one behind the other on a continuous foil (4) and that the other of the conductor elements (6b) is placed on the PTC element (14) by folding the foil (4). [4] Method according to one of the preceding claims, characterized by that after the other of the conductor elements (6b) has been placed, the layer structure consisting of the layers of the foil (4) is pressed with the mass (5), the conductor elements (6) and the PTC element (14) provided therebetween. [5] Method according to one of the preceding claims, characterized by that the mass (5) is a plastic mass which is applied flatly to the film (4) and is adjusted to a Shore A hardness of between 25 and 40 for laying the conductor elements (6). [6] Method according to one of the preceding claims, characterized by that the mass (5) is a cross-linking plastic mass which is pre-cross-linked before the conductor elements (6) are applied. [7] Method according to one of the preceding claims, characterized by that after the other of the conductor elements (6b) has been placed together with the foil (4) adhering thereto, the mass (5) is finally cross-linked by applying external pressure and an elevated temperature.

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