PTC heating element in the form of an integral multi-component plastic part

Abstract

The invention relates to a PTC heating element (10), the connection electrodes (21, 22) of which are made of a highly conductive plastic and which as a whole constitutes an integral multi-component plastic part.

Description

Allod Werkstoff GmbH & Co. KG 00128-26 Fr / sl PTC heating element in the form of a integral multi-component plastic component Technical field of the invention

[0001] The invention relates to a PTC heating element, i.e. a heating element with a positive temperature coefficient, the terminal electrodes of which are made of a highly conductive plastic and which is overall an integral multi-component plastic component. Description of the state of the art

[0002] Positive temperature coefficient (PTC) materials are materials whose electrical resistance increases sharply with rising temperature. For example, PTC plastic materials can consist of a polymer matrix with conductive fillers (e.g., carbon black, metal, or ceramic particles). The conductive path within the material is maintained by the fillers below the threshold temperature. As the temperature increases, the polymer expands, disrupting the conductive paths and increasing the resistance.

[0003] The positive temperature coefficient makes these materials particularly useful for applications such as self-regulating heating elements, temperature sensors, and overcurrent protection devices. For example, PTC heating elements limit their own temperature because increasing resistance automatically reduces the current flow. This prevents overheating without external control. Examples of the use of PTC heating elements in the automotive sector can be found, for example, in DE 102018 113448 A1, DE 102018 113449 A1, and DE 102020 102821 A1.

[0004] With the phasing out of fossil fuels in mobility and energy supply, and the increasing use of electric drives in vehicles and heat pumps in the construction sector, the waste heat previously used for secondary processes such as defrosting in winter and evaporating condensate will no longer be available. As a replacement, electric heating processes have become established in many applications due to the increased use of electrical technologies. Polymer PTC heating elements could play a key role here; however, current challenges exist regarding cost-effective and mass-producible manufacturing as well as recyclability, particularly related to the conventional contact with metallic electrodes embedded at a certain distance within the polymer matrix.This has the disadvantages of a problematic and expensive manufacturing process using injection molding, the contact resistance between metal and plastic, the aging behavior of the contact surface due to different coefficients of thermal expansion, and the difficult recyclability of metal-plastic composite components.

[0005] The object of the invention is to provide PTC heating elements which at least partially overcome the disadvantages described. Brief description of the invention

[0006] Against this background, the invention relates to a heating element comprising a resistance element made of an electrically conductive plastic material with a positive temperature coefficient and at least two terminal electrodes arranged at a distance from one another on the resistance element. According to the invention, the terminal electrodes are made of a highly electrically conductive plastic material with a specific resistance of less than 1 Q*cm (DIN EN ISO 3915:2022-05, 23°C), wherein the plastic material of the terminal electrodes comprises a base plastic and an electrically conductive filler material comprising a fibrous filler in combination with a particulate or substantially spherical filler, and wherein the heating element is an integral multi-component component, the components of which comprise the resistance element and the terminal electrodes.

[0007] The production of the heating elements according to the invention with the monolithic structure can be carried out in particular by multi-component injection molding, by multi-component extrusion or by additive manufacturing.

[0008] The heating elements according to the invention can be used particularly in the field of electric vehicles, where no waste heat from a combustion engine is available and condensation in winter causes problems with many connections, plugs, drain hoses, sensors, etc. due to freezing. The heating elements according to the invention can also find advantageous applications in buildings and in the construction sector. Detailed description of the invention

[0009] The polymeric terminal electrodes form the anode and the cathode of the PTC heating element and are separated from each other by the resistance element made of the PTC plastic material at a defined distance within the PTC heating element.

[0010] In one embodiment, the base plastic of the terminal electrode material may comprise a polyamide (PA), polybutylene terephthalate (PBT), or polypropylene (PP). Suitable polyamides include, for example, PA 66, PA 6, PA 6T, or PA 46. These have a suitable melt flow rate for processing with many electrically conductive plastic materials in multi-component injection molding or multi-component extrusion. The melting temperature (ASTM D3418) of the base plastic should be above the cut-off temperature of the PTC plastic material (see description below) to prevent softening of the resistive element during operation of the PTC heating element.

[0011] In another embodiment, the base plastic of the terminal electrode material may comprise a thermoplastic elastomer (TPE). Suitable thermoplastic elastomers include, for example, thermoplastic polyolefins (TPO) or thermoplastic styrene block copolymers (TPS) such as styrene-ethylene-butylene-styrene (SEBS), styrene / butadiene-styrene (SBS), styrene-ethylene / propylene-styrene (SEPS), or styrene-isoprene-styrene (SIS). Here, too, the melt flow rate can be adjusted within a suitable range for processing with many electrically conductive plastic materials in multi-component injection molding, multi-component extrusion, or additive manufacturing. The use of a thermoplastic elastomer can result in a degree of flexibility in the resistive element and, consequently, the heating element, which may be advantageous in certain applications.

[0012] In yet another embodiment, the base plastic of the terminal electrode material may comprise polyvinylidene fluoride (PVDF), polyetheretherketone (PEEK), or polysulfone (PSU). These materials have high temperature resistance and / or chemical resistance and are suitable for specialized applications.

[0013] According to the invention, the plastic material of the connecting electrodes comprises a base plastic and an electrically conductive filler material, which includes a fibrous filler in combination with a particulate or essentially spherical filler. Due to their high aspect ratio, the fibers form a basic framework for conductivity. The particulate or essentially spherical fillers complement these conductive pathways and fill the gaps between the fibers to create additional contact points, thereby significantly increasing conductivity while still ensuring compatibility with injection molding. The fibrous filler can be carbon fibers. The particulate or essentially spherical filler can be carbon black, graphite, or a combination thereof. Suitable examples include conductive carbon black and expanded graphite.

[0014] The total proportion of filler material in the plastic material of the terminal electrodes can be between 30 and 70 wt.%, preferably between 40 and 60 wt.%. The proportion of fibrous filler in the total filler material can be 20 to 60 wt.%. For example, the plastic material of the terminal electrodes can comprise 30 to 60 wt.% of the base polymer, 25 to 40 wt.% carbon fibers, 10 to 25 wt.% carbon black, and 0 to 40 wt.% graphite. The aforementioned filler levels and mixtures of the different filler materials allow for a low specific resistance while maintaining processability in injection molding, extrusion, or additive manufacturing. The fibrous filler is more expensive and can be enhanced by the addition of particulate or essentially spherical filler.

[0015] Preferably, the plastic material of the connecting electrodes has a specific resistance of less than 0.5 Q*cm or, even better, less than 0.2 Q*cm (DIN EN ISO 3915:2022-05, 23°C).

[0016] The plastic material of the connecting electrodes is of crucial importance within the scope of the invention. This material replaces the metal of the PTC heating elements from the prior art and is intended to exhibit at least comparable electrical properties, be compatible with the PTC plastic material, and be processable in multi-component injection molding, multi-component extrusion, or additive manufacturing.

[0017] The plastic material of the resistive element can be designed such that, within a cutoff temperature range of 50°C to 150°C, a temperature increase of 20°C leads to an increase in electrical resistance of at least a factor of 1.5, or a temperature increase of 40°C leads to an increase in electrical resistance of at least a factor of 4.0, or both. The cutoff temperature defines the temperature at which the electrical resistance of the PTC material increases essentially exponentially with further heating, thus reducing or interrupting the current flow. This temperature threshold is crucial for the self-regulating properties of the PTC material. It is adjusted by selecting the appropriate polymer and filler materials, as well as by determining the filler content.

[0018] The plastic material of the resistance element can have a specific resistance at normal temperature of, for example, less than 500 Q*cm, or less than 200 Q*cm, or less than 100 Q*cm, or less than 75 Q*cm, or less than 50 Q*cm (DIN EN ISO 3915:2022-05, 25°C).

[0019] For the possible choice of the base plastic of the PTC plastic material of the resistance element, reference can be made to the above description of the possible base plastics of the plastic material of the connecting electrodes.

[0020] The plastic materials of the connecting electrodes and the resistance element may each contain additives to improve flowability during injection molding or to enhance material compatibility at the interface within the integral multi-component component. Improved compatibility of the plastic materials leads to enhanced aging resistance and greater stability.

[0021] The heating power can be adjusted, among other things, by the distance between the connecting electrodes and the choice of plastic material for the resistance element. The heating element can be designed for operation at, for example, 12 V, but also for operation at 230 V.

[0022] The integral multi-component component of the heating element according to the invention can, in addition to the plastic materials of the connecting electrodes and the resistance element, also include other components, for example electrically insulating plastic materials or plastics with high thermal conductivity.

[0023] The main advantages of the heating element according to the invention, compared to conventional PTC heating elements with metallic terminal electrodes, include the possibility of simpler and more cost-effective manufacturing and better recyclability of the integral multi-component plastic component.

[0024] In one embodiment, the heating element according to the invention can be plate-shaped and have at least two spaced-apart, rod-shaped terminal electrodes integrated into a plate-shaped resistance element. Such a heating element can, for example, be used for tempering smooth surfaces and can be manufactured using multi-component injection molding.

[0025] In one embodiment, the heating element according to the invention can be sleeve-shaped. The connecting electrodes can be formed by rods extending axially along the sleeve shell, which are integrated into the sleeve-shaped resistance element and optionally interrupt it. Such a heating element can be used, for example, for temperature control of pipes or connections and can be manufactured by multi-component extrusion.

[0026] The production of the heating elements according to the invention can, as already mentioned above, be carried out in particular by multi-component injection molding, by multi-component extrusion or by additive manufacturing.

[0027] Especially in the case of multi-component injection molding, when selecting the base plastics for the terminal electrodes and the resistance element, it is important to ensure that the component molded first has a higher melting point than the component molded later. If the terminal electrodes are molded first, this may mean that the base plastic of the terminal electrode material should have a melting point (ASTM D3418) greater than 200°C. Conversely, if the resistance element is molded first, this may mean that the base plastic of the terminal electrode material should have a melting point (ASTM D3418) less than 180°C.

[0028] As mentioned above, the heating elements according to the invention can be used, for example, in electric vehicles, where no waste heat from a combustion engine is available and condensation in winter causes problems with many connections, plugs, drain hoses, etc., due to freezing. Potential applications in the field of electromobility include, for example, heated floor coverings, heating applications in contacts in batteries and fuel cells, or heating applications in sensor systems for autonomous driving.

[0029] The heating elements according to the invention can also find advantageous applications in buildings and in the construction sector. Examples include, for instance, heating applications for heat pumps as well as heating and ventilation systems.

[0030] Other applications include, for example, wearables or sensors in general, even independently of buildings or vehicles or electric vehicles.

[0031] Further details and advantages of the invention will become apparent from the exemplary embodiments described below with reference to the figures. Brief description of the characters

[0032] The figures show: Fig. 1: A PTC heating element in plate form according to the invention, manufactured by multi-component injection molding. Fig. 2: A diagram of temperature and current over time for the operation of a heating element according to the invention as shown in Fig. 1. Fig. 3: Thermal images taken at three different times during the operation of the heating element according to the invention as shown in Fig. 1. Fig. 4: A PTC heating element in sleeve form according to the invention, produced by multi-component extrusion. Example 1

[0033] A plate-shaped heating element 10, as shown in Fig. 1, comprising a plate-shaped resistance element 11 made of a PTC plastic material and two parallel electrodes 21, 22 made of a highly conductive plastic material, was manufactured by 2K injection molding. The dimensions of the plate of the resistance element 11 were 70 mm x 23 mm x 3.7 mm. The dimensions of the electrodes 21, 22 were 3.9 mm x 2.7 mm. The electrode spacing was 4 mm.

[0034] The highly conductive plastic material of the electrodes 21, 22 comprised 53 wt.% of an adhesion-modified PA 66 as the base plastic, 32 wt.% carbon fibers and 13.5 wt.% conductive carbon black as fillers, and 1.5 wt.% other additives and stabilizers. The specific resistance of the highly conductive plastic material was 0.1 Q*cm (DIN EN ISO 3915:2022-05, 23°C).

[0035] The PTC plastic material of resistance element 11 comprised 67 wt% of a TPS-SEBS base plastic, 32 wt% conductive carbon black as filler, and 1 wt% other additives and stabilizers. The specific resistance of the highly conductive plastic material was 41 Q*cm (DIN EN ISO 3915:2022-05, 23°C) and is strongly temperature-dependent, with a positive temperature coefficient.

[0036] Fig. 2 shows a diagram of the temperature of the resistance element 11 and current when the electrodes 21, 22 are contacted with 12 V as a function of time. Fig. 3 shows thermal images taken at three different times during operation. It can be seen that the PTC heating element 10 reaches its cut-off temperature of approximately 70°C after about 5 minutes. The heating of the surface of the resistance element 11 is uniform, and the overall performance is satisfactory and comparable to prior art PTC heating elements with metallic electrodes.

[0037] No problems arose during the production of the heating element 10 using 2K injection molding, and the performance was, as demonstrated, very satisfactory. It would therefore be suitable for use in heating surfaces in the automotive or construction sectors and could be mass-produced cost-effectively. Its recyclability is significantly improved compared to conventional flat PTC heating elements with metallic electrodes. Example 2

[0038] A sleeve-shaped heating element 10, as shown in Fig. 4, was manufactured by 2K extrusion. The connecting electrodes 21, 22 are formed by sections extending axially along the sleeve shell, which are integrated into and interrupt the sleeve-shaped resistance element 11.

[0039] No problems arose during the manufacturing of the heating element shown in Fig. 4, and its performance was also very satisfactory. It would therefore be suitable for use in heating, for example, connections, plugs, drain hoses, etc., and could be mass-produced cost-effectively. Its recyclability is significantly improved compared to prior art sleeve-shaped PTC heating elements with metallic electrodes.

Claims

Claims 1. Heating element comprising a resistance element made of an electrically conductive plastic material with a positive temperature coefficient and at least two terminal electrodes arranged at a distance from each other on the resistance element, characterized by that the terminal electrodes are made of an electrically highly conductive plastic material with a specific resistance of less than 1 Q*cm (DIN EN ISO 3915:2022-05, 23°C), wherein the plastic material of the terminal electrodes comprises a base plastic and an electrically conductive filler material comprising a fibrous filler in combination with a particulate or substantially spherical filler, and that the heating element is an integral multi-component component, the components of which comprise the resistance element and the terminal electrodes.

2. Heating element according to claim 1, wherein the base plastic of the plastic material of the connecting electrodes comprises a polyamide, polybutylene terephthalate or a polypropylene.

3. Heating element according to claim 1, wherein the base plastic of the plastic material of the connecting electrodes comprises a thermoplastic elastomer.

4. Heating element according to claim 1, wherein the base plastic of the plastic material of the connecting electrodes comprises a polyvinylidene fluoride, a polyetheretherketone or a polysulfone.

5. Heating element according to any of the preceding claims, wherein the fibrous filler is carbon fibers, and / or wherein the particulate or substantially spherical filler is carbon black, graphite or a combination thereof.

6. Heating element according to one of the preceding claims, wherein the total proportion of the filler material in the plastic material of the connecting electrodes is between 30-70 wt.%, preferably between 40-60 wt.%.

7. Heating element according to one of the preceding claims, wherein the proportion of the fibrous filler in the total filler material is 20-60 wt.%.

8. Heating element according to one of the preceding claims, wherein the plastic material of the connecting electrodes has a specific resistance of less than 0.5 Q*cm, preferably less than 0.2 Q*cm (DIN EN ISO 3915:2022-05, 23°C).

9. Heating element according to one of the preceding claims, wherein the plastic material of the resistance element is designed such that in the range of a cut-off temperature which may be between 50°C and 150°C, a temperature increase of 20°C leads to an increase in electrical resistance by at least a factor of 1.5, or a temperature increase of 40°C leads to an increase in electrical resistance by at least a factor of 4.0, or both.

10. Heating element according to one of the preceding claims, wherein the plastic material of the resistance element has a specific resistance at normal temperature of less than 500 Q*cm, preferably less than 100 Q*cm, further preferably less than 50 Q*cm (DIN EN ISO 3915:2022-05, 23°C).

11. Heating element according to one of the preceding claims, wherein the heating element is plate-shaped and has at least two rod-shaped terminal electrodes spaced apart from each other, which are integrated into a plate-shaped resistance element.

12. Heating element according to one of the preceding claims, wherein the heating element is sleeve-shaped and the connecting electrodes are formed by rods extending axially along the sleeve shell, which are integrated into the sleeve-shaped resistance element and optionally interrupt it.

13. Method for manufacturing a heating element according to one of the preceding claims, characterized in that the heating element is manufactured by multi-component injection molding, by multi-component extrusion or by additive manufacturing.

14. Use of a heating element according to any one of claims 1-12 in an electric vehicle.

15. Use of a heating element according to any one of claims 1-12 in buildings.

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