EP1231613A1 - Resistance elements showing PTC-behaviour - Google Patents

Resistance elements showing PTC-behaviour Download PDF

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Publication number
EP1231613A1
EP1231613A1 EP01810131A EP01810131A EP1231613A1 EP 1231613 A1 EP1231613 A1 EP 1231613A1 EP 01810131 A EP01810131 A EP 01810131A EP 01810131 A EP01810131 A EP 01810131A EP 1231613 A1 EP1231613 A1 EP 1231613A1
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EP
European Patent Office
Prior art keywords
composite
resistance
resistance element
filler
electrodes
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01810131A
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German (de)
French (fr)
Inventor
Joachim Glatz-Reichenbach
Ruzica Loitzl-Jelenic
Ralf Strümpler
Timo Jokiniemi
Erkki Rajala
Jarkko Alanen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ABB Research Ltd Switzerland
ABB Research Ltd Sweden
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ABB Research Ltd Switzerland
ABB Research Ltd Sweden
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Application filed by ABB Research Ltd Switzerland, ABB Research Ltd Sweden filed Critical ABB Research Ltd Switzerland
Priority to EP01810131A priority Critical patent/EP1231613A1/en
Publication of EP1231613A1 publication Critical patent/EP1231613A1/en
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C1/00—Details
    • H01C1/14—Terminals or tapping points or electrodes specially adapted for resistors; Arrangements of terminals or tapping points or electrodes on resistors
    • H01C1/1406—Terminals or electrodes formed on resistive elements having positive temperature coefficient
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
    • H01C17/28—Apparatus or processes specially adapted for manufacturing resistors adapted for applying terminals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
    • H01C17/28—Apparatus or processes specially adapted for manufacturing resistors adapted for applying terminals
    • H01C17/281—Apparatus or processes specially adapted for manufacturing resistors adapted for applying terminals by thick film techniques
    • H01C17/283—Precursor compositions therefor, e.g. pastes, inks, glass frits
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/02—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
    • H01C7/027—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient consisting of conducting or semi-conducting material dispersed in a non-conductive organic material

Definitions

  • the invention is based on resistance elements according to the Preambles of claims 1, 3 and 6.
  • Such resistance elements each contain a resistance body from a PTC behavior comprising composite based on a filler-filled polymer and two electrodes electrically contacting the resistance body.
  • Such Resistance elements are preferred as self-regulating heating resistors Sensors or as an overcurrent limiter, especially in the low-voltage range, used.
  • the composite is based on mixing filler an electrically conductive powder is formed in a polymer matrix. Is considered If a polymer uses a thermoplastic, the composite becomes at temperatures formed, in which the thermoplastic is flowable. It can then still from the flowable composite by thermoforming, such as extrusion or spray or Extrusion, resistance body generated and subsequent or during the formation with formation of the resistance elements with the two electrodes be provided.
  • PTC resistance elements are the electrodes as plates, foils or reticulated metal parts executed, which by means of an intermediate layer of a liquid metal or an electrically conductive polymer on the Resistor body applied or molded directly into the resistance body are.
  • a liquid metal makes it difficult to manufacture one Resistance element quite considerably.
  • the resistance element Although easy to manufacture, it is then undesirable mechanical Exposed to tension, which may affect its functionality can significantly affect. These mechanical tensions can because of the different thermal expansion coefficients of composite and electrode when cooling a resistance element during the Manufacturing process or also occur during operation and can be particularly disadvantageous with a large-sized resistance element impact, such as this for current limitation in plants and Apparatus with large operating currents and / or voltages is used.
  • the invention as defined in the claims solves the problem Specify resistance elements of the type mentioned, which is simple are to be produced, and their functionality even after multiple Current limitation in large currents and / or voltages exposed Device or system is still guaranteed with certainty.
  • At least one of the two electrodes contains each of the Resistance elements a flexible metal foam or is at least one of the formed both electrodes as a rigid metal body and has this Metal body filled with composite recesses and / or passages on or is at least one of the two electrodes formed by a composite with a polymer matrix and a powdery filler embedded in the matrix.
  • Electrodes designed in this way can be used to manufacture the electrodes according to the invention Resistance elements in a simple manner in the resistance body be melted down. Through the training of the Electrodes is achieved when the temperature of the PTC resistance elements occurring between electrode and resistance body mechanical stresses cause no damage and so the Functionality of the resistance elements is not reduced.
  • the build-up of voltages occurs in the embodiment of the PTC resistance element with flexible metal foam avoided that when heating or cooling the resistance element, the composite expands or contracts considerably more than the metal foam, which itself however, because of its high flexibility through practically force-free deformation can adapt stress-free to the changed geometry of the composite. It It is recommended that at least a part of the metal foam with composite has filled, open pores. Then it is a particularly good mechanical one Installation of the metal foam in the resistance body ensures and it will at the same time the contact resistance between the electrode and the resistance body reduced.
  • the electrode as a rigid metal body with depressions and / or passages executed, the composite material of the resistance body in the recesses and / or passages.
  • the through the different Coefficient of thermal expansion of metal and composite Mechanical stresses arising from thermal stress can thus be used Formation of a high contact force between metal body and composite and so that a desirable low contact resistance can be exploited.
  • Particularly good adhesion of the composite to the metal body is achieved if at least some of the recesses are blind holes, and / or if the depressions are formed by a roughened Surface with a surface roughness that is greater than the middle one Grain size of the filler contained in the polymer.
  • a particularly good liability is achieved when the roughness is greater than the dimensions of the largest particle provided in the filler.
  • the electrode is formed from a composite material with a Polymer matrix and a powdery filler embedded in the matrix a ductile and high electrical conductivity material or Made of a composite with a polymer matrix that has a higher melting point has as the polymer matrix of the resistance body, and one in the matrix embedded powdered filler made of an electrically conductive ceramic or a low ductility metal, such as nickel, have electrode and Resistor body of the PTC resistance element according to the invention practically have the same coefficients of thermal expansion. Mechanical stresses in the PTC resistance elements are thus avoided when exposed to temperature and it will also have a good long-term behavior of the resistance element repeated execution of a current-limiting PTC transition reached.
  • the 1 shows a PTC resistance element only partially shown Resistor body 1 made of a composite based on a filler Polymers.
  • a composite can, for example, be a Titanium diboride powder filled polyethylene.
  • the powder shows here typically 20 to 60 percent by volume of the composite and can Have grain sizes from a few to 100 and more microns.
  • Composition and The structure of the composite can vary depending on the area of application of the PTC resistance element can be changed within wide limits.
  • the resistance body 1 is electrically conductively connected to two electrodes, from which one can be seen from Fig.1.
  • This electrode has the reference symbol 2 marked.
  • the electrode 2 contains metal foam made of a metal, for example based on nickel.
  • the metal foam is preferably after Formed like a sponge and then has open composite filled with composite Pores on.
  • the electrode 2 is in an electrically conductive manner with a metallic Power connector 3 connected, which is special in manufacturing technology can advantageously be formed by pressing metal foam.
  • the to the power connection 3 pressed metal foam and the one filled with composite and metal foam forming electrode 2 were before filling the open ones Pores with composite part of a flexible body made of metal foam.
  • the PTC resistance element was integrated into the electrode 2 Part of this body and possibly a corresponding part of another one Body for the second electrode, not shown, inserted into a mold and this mold filled with liquid composite under pressure and temperature. in this connection liquid composite could enter the open pores of the metal foam body penetration. That by cooling - when using a thermoset or Elastomer as a polymer by curing - formed PTC resistance element was removed from the mold and the part of the Metal foam body deformed by pressing to the power connection 3.
  • the PTC resistance element described above heats up during of a PTC transition and then cools down again.
  • the different coefficients of thermal expansion of metal and composite Mechanical stresses caused are avoided by the fact that the Metal foam is deformed practically without force due to its high flexibility accordingly, stress-free to the changed geometry of the composite adapts. Detachment of the electrode 2 and thus an increase in the Transition resistance in the area of the electrode is certain avoided.
  • By filling part of the open pores of the metal foam with Composite is a particularly good mechanical installation of the metal foam in ensures the resistance body and at the same time becomes the contact resistance reduced between electrode 2 and resistance body 1.
  • a PTC resistance element with two nickel foam electrodes was produced from nickel foam and a polyethylene filled with 50 percent by volume titanium diboride.
  • the contact resistance Ro was measured on this PTC resistance element at room temperature (23 ° C.) immediately after production.
  • the contact resistance Ro ' was measured on the same resistance element after ten treatment cycles, each comprising 24-hour storage at 60 ° C. and cooling to room temperature.
  • the measured values of Ro and Ro ', the quotient Ro' / Ro describing the increase in the contact resistance of the PTC resistance element and the relative contact resistance in percent, based on a test resistance of 1 cm length and 0.8 cm 2 diameter, are at the end of the Description entered in a table as example 1.
  • the electrode 2 is of a rigid, predominantly plate-shaped metal body, for example made of aluminum, brass or a with nickel-coated copper body.
  • plate 6 formed part of the metal body are passages 4 filled with composite and / or depressions 5 are formed.
  • the wells 5 can at least Part be designed as blind holes, but can also be formed by a roughened surface with a surface roughness that is greater than the average grain size of the filler contained in the polymer.
  • the metal body is generally designed as a plate. He can hit the plate molded legs 7, which an additional improvement in Anchor the resistance body 1 serve. One of the legs can also be provided for carrying the power connection 3.
  • Two PTC resistance elements designed in accordance with FIGS. 2 and 3 were produced from two aluminum or brass bodies and a polyethylene filled with 50 percent by volume titanium diboride.
  • the contact resistance Ro was measured on these resistance elements at room temperature (23 ° C.) immediately after production.
  • the contact resistance Ro ' was measured on the same resistance elements after ten treatment cycles, each comprising 24-hour storage at 60 ° C. and cooling to room temperature.
  • the measured values of Ro and Ro ', the quotient Ro' / Ro describing the increase in the contact resistance of the PTC resistance element and the relative contact resistance in percent, based on a test resistance of 1 cm length and 0.8 cm 2 diameter, are in the am At the end of the description table provided as examples 2 and 3.
  • one of the PTC resistance elements according to the Invention is formed from a composite with an electrode Polymer matrix and a powdery filler embedded in the matrix a ductile and high electrical conductivity material. Electrode 2 and resistance body 1 of the PTC resistance element according to the invention have practically the same in this embodiment Coefficients of thermal expansion. Mechanical stresses in the PTC resistance element are thus avoided under temperature loads and it will good long-term behavior of the resistance element even after repeated Execution of a current-limiting PTC transition reached.
  • a suitable one Composite is one with a powder based on silver, gold and / or copper filled polymer, which is advantageously the same polymer as that in the composite the resistance body provided, for example polyethylene. On this electrically excellent conductive composite can then easily be used as a Pressure contact trained metallic power connector can be attached.
  • a PTC resistance element with a resistance body made of a titanium-containing polyethylene and two silver-polyethylene composite electrodes was produced from a polyethylene filled with 50 volume percent silver powder and a polyethylene filled with 50 volume percent titanium diboride powder.
  • This PTC resistance element was provided with two pressure contacts and the contact resistance Ro was measured immediately after manufacture at room temperature (23 ° C.). The contact resistance Ro 'was measured on the same resistance element after ten treatment cycles, each comprising 24-hour storage at 60 ° C. and cooling to room temperature, and after the pressure contacts had been applied.
  • the measured values of Ro and Ro ', the quotient Ro' / Ro describing the increase in the contact resistance of the PTC resistance element and the relative contact resistance in percent, based on a test resistance of 1 cm in length and 0.8 cm 2 in diameter, are as follows Table entered as example 4.
  • a comparative example I in which the pressure contacts were pressed directly onto the titanium diboride-containing resistor body and a comparative example II in which two nickel foils used as electrodes were embedded in the resistor body are also entered in the table.
  • the electrode can also be formed from a composite, which contains a polymer matrix that has a higher melting point than the polymer matrix of the resistance body, and one embedded in the matrix powdered filler made of an electrically conductive ceramic or a metal low ductility.
  • This electrode leads at a higher temperature than that Resistor body from a PTC transition. Will a place of Resistor body locally overheats when limiting the current and the current can over this local point continues to flow, the overheating is triggered with a time delay in the Electrode a second PTC transition, which limits the current and so prevents failure of the PTC resistance element.

Abstract

In a resistor element with a resistor body (1) of a composite material with a positive temperature coefficient (PTC) based on filled polymer and two electrodes (2), at least one of the electrodes contains a flexible metal sponge. Independent claims are also included for the following: (1) a resistor element with a body of PTC-type composite material and two electrodes, at least one of which comprises a rigid metal body with cavities and/or vias filled with composite; (2) a resistor element with a body of PTC-type composite material and two electrodes, at least one of which comprises a composite of either a polymer matrix and embedded powdered filler of a ductile, electroconductive material or a polymer matrix with higher melting point than that of the composite and an electroconductive ceramic or a metal with low ductility.

Description

TECHNISCHES GEBIETTECHNICAL AREA

Bei der Erfindung wird ausgegangen von Widerstandselementen nach den Oberbegriffen der Patentansprüche 1, 3 und 6. Solche Widerstandselemente enthalten jeweils einen Widerstandskörper aus einem PTC-Verhalten aufweisenden Verbundstoff auf der Basis eines füllstoffgefüllten Polymers sowie zwei den Widerstandskörper elektrisch kontaktierende Elektroden. Derartige Widerstandselemente werden bevorzugt als selbstregelnde Heizwiderstände, als Sensoren oder als Überstrombegrenzer, insbesondere im Niederspannugsbereich, verwendet. Der Verbundstoff wird durch Einmischen von Füllstoff auf der Basis eines elektrisch leitfähigen Pulvers in eine Polymermatrix gebildet. Wird als Polymer ein Thermoplast verwendet, so wird der Verbundstoff bei Temperaturen gebildet, bei denen der Thermoplast fliessfähig ist. Es können dann aus dem noch fliessfähigen Verbundstoff durch Warmformen, wie etwa Extrudieren oder Spritzoder Strangpressen, Widerstandskörper erzeugt und nachfolgend oder während der Formung unter Bildung der Widerstandselemente mit den beiden Elektroden versehen werden.The invention is based on resistance elements according to the Preambles of claims 1, 3 and 6. Such resistance elements each contain a resistance body from a PTC behavior comprising composite based on a filler-filled polymer and two electrodes electrically contacting the resistance body. such Resistance elements are preferred as self-regulating heating resistors Sensors or as an overcurrent limiter, especially in the low-voltage range, used. The composite is based on mixing filler an electrically conductive powder is formed in a polymer matrix. Is considered If a polymer uses a thermoplastic, the composite becomes at temperatures formed, in which the thermoplastic is flowable. It can then still from the flowable composite by thermoforming, such as extrusion or spray or Extrusion, resistance body generated and subsequent or during the formation with formation of the resistance elements with the two electrodes be provided.

STAND DER TECHNIKSTATE OF THE ART

Mit den Oberbegriffen der Patentansprüche 1, 3 und 6 nimmt die Erfindung auf einen Stand der Technik von PTC-Widerstandselementen Bezug, wie er etwa in in DE 198 42 124 A1, EP 0 758 131 A2 oder WO 97/06660 A2 angegeben ist. Bei diesen PTC-Widerstandselementen sind die Elektroden als platten-, folien- oder netzförmige Metallteile ausgeführt, welche mittels einer Zwischenschicht aus einem flüssigen Metall oder aus einem elektrisch leitenden Polymer auf den Widerstandskörper aufgebracht oder direkt in den Widerstandskörper eingeformt sind. Die Verwendung eines flüssigen Metalls erschwert die Herstellung eines Widerstandselementes ganz erheblich. Werden die Elektroden ohne flüssiges Metall direkt oder mittels eines polymeren Klebers auf den Widerstandskörper aufgebracht oder in den Widerstandskörper eingeformt, so kann das Widerstandselement zwar leicht gefertigt werden, ist dann aber unerwünschten mechanischen Spannungen ausgesetzt, welche dessen Funktionsfähigkeit gegebenenfalls wesentlich beinträchtigen können. Diese mechanischen Spannungen können wegen der unterschiedlichen Wärmeausdehnungskoeffizienten von Verbundstoff und Elektrode beim Abkühlen eines Widerstandselements während des Herstellungsprozesses oder aber auch während des Betriebseinsatzes auftreten und können sich besonders nachteilig bei einem gross bemessenen Widerstandselement auswirken, so wie dies etwa zur Strombegrenzung in Anlagen und Apparaten mit grossen Betriebsströmen und/oder -spannungen eingesetzt wird.With the preambles of claims 1, 3 and 6, the invention takes up a state of the art of PTC resistance elements reference, such as in in DE 198 42 124 A1, EP 0 758 131 A2 or WO 97/06660 A2 is specified. at These PTC resistance elements are the electrodes as plates, foils or reticulated metal parts executed, which by means of an intermediate layer of a liquid metal or an electrically conductive polymer on the Resistor body applied or molded directly into the resistance body are. The use of a liquid metal makes it difficult to manufacture one Resistance element quite considerably. If the electrodes are without liquid Metal directly or using a polymer adhesive on the resistance body applied or molded into the resistance body, the resistance element Although easy to manufacture, it is then undesirable mechanical Exposed to tension, which may affect its functionality can significantly affect. These mechanical tensions can because of the different thermal expansion coefficients of composite and electrode when cooling a resistance element during the Manufacturing process or also occur during operation and can be particularly disadvantageous with a large-sized resistance element impact, such as this for current limitation in plants and Apparatus with large operating currents and / or voltages is used.

DARSTELLUNG DER ERFINDUNGPRESENTATION OF THE INVENTION

Die Erfindung, wie sie in den Patentansprüchen definiert ist, löst die Aufgabe, Widerstandselemente der eingangs genannten Art anzugeben, welche einfach herzustellen sind, und deren Funktionsfähigkeit auch nach mehrfacher Strombegrenzung in einer grossen Strömen und/oder Spannungen ausgesetzten Vorrichtung oder Anlage noch mit Sicherheit gewährleistet ist.The invention as defined in the claims solves the problem Specify resistance elements of the type mentioned, which is simple are to be produced, and their functionality even after multiple Current limitation in large currents and / or voltages exposed Device or system is still guaranteed with certainty.

Bei der Erfindung enthält mindestens eine der beiden Elektroden jedes der Widerstandselemente einen flexiblen Metallschaum oder ist mindestens eine der beiden Elektroden als starrer Metallkörper ausgebildet und weist dieser Metallkörper mit Verbundstoff gefüllte Vertiefungen und/oder Durchlässe auf oder ist mindestens eine der beiden Elektroden von einem Verbundstoff gebildet mit einer Polymermatrix und einem in die Matrix eingebetteten pulverförmigen Füllstoff. Derartig ausgebildete Elektroden können beim Herstellen der erfindungsgemässen Widerstandselemente in einfacher Weise in den Widerstandskörper eingeschmolzen werden. Durch die vorstehend beschriebenen Ausbildungen der Elektroden wird erreicht, dass bei Temperaturbelastung der PTC-Widerstandselemente zwischen Elektrode und Widerstandskörper auftretende mechanische Spannungen keine Schäden verursachen und so die Funktionsfähigkeit der Widerstandselemente nicht herabgesetzt wird.In the invention, at least one of the two electrodes contains each of the Resistance elements a flexible metal foam or is at least one of the formed both electrodes as a rigid metal body and has this Metal body filled with composite recesses and / or passages on or is at least one of the two electrodes formed by a composite with a polymer matrix and a powdery filler embedded in the matrix. Electrodes designed in this way can be used to manufacture the electrodes according to the invention Resistance elements in a simple manner in the resistance body be melted down. Through the training of the Electrodes is achieved when the temperature of the PTC resistance elements occurring between electrode and resistance body mechanical stresses cause no damage and so the Functionality of the resistance elements is not reduced.

Sich aufbauende Spannungen werden bei der Ausführungsform des PTC-Widerstandselements mit flexiblem Metallschaum dadurch vermieden, dass sich beim Erwärmen oder Abkühlen des Widerstandselements zwar der Verbundstoff erheblich stärker ausdehnt oder zusammenzieht als der Metallschaum, dieser sich jedoch wegen seiner hohen Flexibilität durch praktisch kräftefreies Verformen spannungsfrei an die veränderte Geometrie des Verbundstoffs anpassen kann. Es empfiehlt sich, dass zumindest ein Teil des Metallschaums mit Verbundstoff gefüllte, offene Poren aufweist. Es ist dann ein besonders guter mechanischer Einbau des Metallschaums in den Widerstandskörper gewährleistet und es wird zugleich der Übergangswiderstand zwischen Elektrode und Widerstandskörper reduziert.The build-up of voltages occurs in the embodiment of the PTC resistance element with flexible metal foam avoided that when heating or cooling the resistance element, the composite expands or contracts considerably more than the metal foam, which itself however, because of its high flexibility through practically force-free deformation can adapt stress-free to the changed geometry of the composite. It It is recommended that at least a part of the metal foam with composite has filled, open pores. Then it is a particularly good mechanical one Installation of the metal foam in the resistance body ensures and it will at the same time the contact resistance between the electrode and the resistance body reduced.

Ist die Elektrode als starrer Metallkörper mit Vertiefungen und/oder Durchlässen ausgeführt, so wird der Verbundstoff des Widerstandskörpers in den Vertiefungen und/oder Durchlässen festgesetzt. Die durch die unterschiedlichen Wärmeausdehnungskoeffizienten von Metall und Verbundstoff bei Temperaturbelastung entstehenden mechanischen Spannungen können so zur Bildung einer hohen Kontaktkraft zwischen Metallkörper und Verbundstoff und damit eines wünschenswert kleinen Übergangswiderstands ausgenutzt werden. Eine besonders gute Haftung des Verbundstoffs am Metallkörper wird erreicht, wenn zumindest ein Teil der Vertiefungen als Blindbohrungen ausgeführt ist, und/oder wenn die Vertiefungen gebildet werden durch eine aufgerauhte Oberfläche mit einer Oberflächenrauhigkeit, welche grösser ist als die mittlere Korngrösse des im Polymer enthaltenen Füllstoffs. Eine besonders gute Haftung wird erreicht, wenn die Rauhigkeit grösser ist als die Abmessungen des grössten im Füllstoff vorgesehenen Teilchens.Is the electrode as a rigid metal body with depressions and / or passages executed, the composite material of the resistance body in the recesses and / or passages. The through the different Coefficient of thermal expansion of metal and composite Mechanical stresses arising from thermal stress can thus be used Formation of a high contact force between metal body and composite and so that a desirable low contact resistance can be exploited. Particularly good adhesion of the composite to the metal body is achieved if at least some of the recesses are blind holes, and / or if the depressions are formed by a roughened Surface with a surface roughness that is greater than the middle one Grain size of the filler contained in the polymer. A particularly good liability is achieved when the roughness is greater than the dimensions of the largest particle provided in the filler.

Ist hingegen die Elektrode von einem Verbundstoff gebildet mit einer Polymermatrix und einem in die Matrix eingebetteten pulverförmigen Füllstoff aus einem duktilen und eine hohe elektrische Leitfähigkeit aufweisenden Material oder aus einem Verbundstoff mit einer Polymermatrix, die einen höheren Schmelzpunkt aufweist als die Polymermatrix des Widerstandskörpers, und einem in die Matrix eingebetteten pulverförmigen Füllstoff aus einer elektrische leitfähigen Keramik oder einem Metall geringer Duktilität, wie etwa Nickel, so weisen Elektrode und Widerstandskörper des erfindungsgemässen PTC-Widerstandselementes praktisch die gleichen Wärmeausdehnungskoeffizenten auf. Mechanische Spannungen im PTC-Widerstandselement werden so bei Temperaturbelastung vermieden und es wird ein gutes Langzeitverhalten des Widerstandselementes auch nach wiederholtem Ausführen eines strombegrenzenden PTC-Überganges erreicht.If, on the other hand, the electrode is formed from a composite material with a Polymer matrix and a powdery filler embedded in the matrix a ductile and high electrical conductivity material or Made of a composite with a polymer matrix that has a higher melting point has as the polymer matrix of the resistance body, and one in the matrix embedded powdered filler made of an electrically conductive ceramic or a low ductility metal, such as nickel, have electrode and Resistor body of the PTC resistance element according to the invention practically have the same coefficients of thermal expansion. Mechanical stresses in the PTC resistance elements are thus avoided when exposed to temperature and it will also have a good long-term behavior of the resistance element repeated execution of a current-limiting PTC transition reached.

KURZE BESCHREIBUNG DER ZEICHNUNGENBRIEF DESCRIPTION OF THE DRAWINGS

Die Erfindung wird nachstehend anhand von Ausführungsbeispielen erläutert. Es zeigt:

Fig. 1
eine Ansicht einer ersten Ausführungsform des Widerstandselements nach der Erfindung im Bereich eines seiner beiden Stromanschlüsse,
Fig. 2
eine Aufsicht auf eine zweite Ausführungsform des Widerstandselements nach der Erfindung, und
Fig.3
eine von von links geführte Seitenansicht des Widerstandselements gemäss Fig.2 im Bereich eines seiner beiden Stromanschlüsse.
The invention is explained below using exemplary embodiments. It shows:
Fig. 1
2 shows a view of a first embodiment of the resistance element according to the invention in the area of one of its two current connections,
Fig. 2
a plan view of a second embodiment of the resistance element according to the invention, and
Figure 3
a left-hand side view of the resistance element according to Figure 2 in the area of one of its two power connections.

WEGE ZUR AUSFÜHRUNG DER ERFINDUNGWAYS OF CARRYING OUT THE INVENTION

In den Figuren sind gleiche Teile mit gleichen Bezugszeichen gekennzeichnet. Das in Fig. 1 nur teilweise dargestellte PTC-Widerstandselement weist einen Widerstandskörper 1 aus einem Verbundstoff auf der Basis eines füllstoffgefüllten Polymers auf. Ein solcher Verbundstoff kann beispielsweise ein mit Titandiboridpulver gefülltes Polyäthylen sein. Das Pulver weist hierbei typischerweise 20 bis 60 Volumenprozent Anteil am Verbundstoff auf und kann Körngrössen von einigen bis 100 und mehr µm aufweisen. Zusammensetzung und Struktur des Verbundstoffs können je nach Anwendungsbereich des PTC-Widerstandselementes in weiten Grenzen geändert werden.In the figures, the same parts are identified by the same reference numerals. The 1 shows a PTC resistance element only partially shown Resistor body 1 made of a composite based on a filler Polymers. Such a composite can, for example, be a Titanium diboride powder filled polyethylene. The powder shows here typically 20 to 60 percent by volume of the composite and can Have grain sizes from a few to 100 and more microns. Composition and The structure of the composite can vary depending on the area of application of the PTC resistance element can be changed within wide limits.

Der Widerstandskörper 1 ist mit zwei Elektroden elektrisch leitend verbunden, von denen eine aus der Fig.1 ersichtlich ist. Diese Elektrode ist mit dem Bezugszeichen 2 gekennzeichnet. Die Elektrode 2 enthält Metallschaum aus einem Metall, beispielsweise auf der Basis von Nickel. Der Metallschaum ist vorzugsweise nach Art eines Schwammes ausgebildet und weist dann mit Verbundstoff gefüllte, offene Poren auf. Die Elektrode 2 ist in elektrisch leitender Weise mit einem metallischen Stromanschluss 3 verbunden, welcher in fertigungstechnisch besonders vorteilhafter Weise durch Verpressen von Metallschaum gebildet werden kann. Der zum Stromanschluss 3 verpresste Metallschaum und der mit Verbundstoff gefüllte und die Elektrode 2 bildende Metallschaum waren vor dem Füllen der offenen Poren mit Verbundstoff Teil eines flexiblen Körpers aus dem Metallschaum. Beim Herstellen des PTC-Widerstandselements wurden der in die Elektrode 2 integrierte Teil dieses Körper und gegebenfalls ein entsprechender Teil eines weiterer solchen Körpers für die nicht dargestellte zweite Elektrode in eine Form eingeführt und diese Form unter Druck und Temperatur mit flüssigem Verbundstoff gefüllt. Hierbei konnte flüssiger Verbundstoff in die offenen Poren des Metallschaumkörpers eindringen. Das durch Abkühlen - bei Verwendung eines Duroplasts oder Elastomers als Polymer durch Aushärten - gebildete PTC-Widerstandselement wurde aus der Form entfernt und der nicht mit Verbundstoff gefüllte Teil des Metallschaumkörpers durch Verpressen zum Stromanschluss 3 verformt.The resistance body 1 is electrically conductively connected to two electrodes, from which one can be seen from Fig.1. This electrode has the reference symbol 2 marked. The electrode 2 contains metal foam made of a metal, for example based on nickel. The metal foam is preferably after Formed like a sponge and then has open composite filled with composite Pores on. The electrode 2 is in an electrically conductive manner with a metallic Power connector 3 connected, which is special in manufacturing technology can advantageously be formed by pressing metal foam. The to the power connection 3 pressed metal foam and the one filled with composite and metal foam forming electrode 2 were before filling the open ones Pores with composite part of a flexible body made of metal foam. At the Manufacture of the PTC resistance element was integrated into the electrode 2 Part of this body and possibly a corresponding part of another one Body for the second electrode, not shown, inserted into a mold and this mold filled with liquid composite under pressure and temperature. in this connection liquid composite could enter the open pores of the metal foam body penetration. That by cooling - when using a thermoset or Elastomer as a polymer by curing - formed PTC resistance element was removed from the mold and the part of the Metal foam body deformed by pressing to the power connection 3.

Das vorstehend beschriebene PTC-Widerstandselement erwärmt sich während eines PTC-Überganges stark und kühlt sich danach wieder ab. Durch die unterschiedlichen Wärmeausdehnungskoeffizienten von Metall und Verbundstoff verursachte mechanische Spannungen werden dadurch vermieden, dass sich der Metallschaum wegen seiner hohen Flexibilität praktisch kräftefrei verformt und sich dementsprechend spannungsfrei an die veränderte Geometrie des Verbundstoffs anpasst. Ein Ablösen der Elektrode 2 und damit eine Erhöhung des Übergangswiderstandes im Bereich der Elektrode werden so mit Sicherheit vermieden. Durch Auffüllen eines Teils der offenen Poren des Metallschaums mit Verbundstoff ist ein besonders guter mechanischer Einbau des Metallschaums in den Widerstandskörper gewährleistet und wird zugleich der Übergangswiderstand zwischen Elektrode 2 und Widerstandskörper 1 reduziert.The PTC resistance element described above heats up during of a PTC transition and then cools down again. Through the different coefficients of thermal expansion of metal and composite Mechanical stresses caused are avoided by the fact that the Metal foam is deformed practically without force due to its high flexibility accordingly, stress-free to the changed geometry of the composite adapts. Detachment of the electrode 2 and thus an increase in the Transition resistance in the area of the electrode is certain avoided. By filling part of the open pores of the metal foam with Composite is a particularly good mechanical installation of the metal foam in ensures the resistance body and at the same time becomes the contact resistance reduced between electrode 2 and resistance body 1.

Aus Nickelschaum und einem mit 50 Volumenprozent Titandiborid gefüllten Polyäthylen wurde gemäss Fig.1 ein PTC-Widerstandselement mit zwei Nickelschaumelektroden gefertigt. An diesem PTC-Widerstandselement wurde bei Raumtemperatur (23°C) der Kontaktwiderstand Ro unmittelbar nach der Fertigung gemessen. Am gleichen Widerstandselement wurde der Kontaktwiderstand Ro' nach zehn Behandlungszyklen, welche jeweils eine 24-stündige Einlagerung bei 60°C und Abkühlung auf Raumtemperatur umfassen, gemessen. Die Messwerte von Ro und Ro', der die Zunahme des Kontaktwiderstands des PTC-Widerstandselements beschreibenden Quotient Ro'/Ro und der relative Kontaktwiderstand in Prozent, bezogen auf einen Probewiderstand von 1 cm Länge und 0,8 cm2 Durchmesser, sind am Schluss der Beschreibung in einer Tabelle als Beispiel 1 eingetragen.A PTC resistance element with two nickel foam electrodes was produced from nickel foam and a polyethylene filled with 50 percent by volume titanium diboride. The contact resistance Ro was measured on this PTC resistance element at room temperature (23 ° C.) immediately after production. The contact resistance Ro 'was measured on the same resistance element after ten treatment cycles, each comprising 24-hour storage at 60 ° C. and cooling to room temperature. The measured values of Ro and Ro ', the quotient Ro' / Ro describing the increase in the contact resistance of the PTC resistance element and the relative contact resistance in percent, based on a test resistance of 1 cm length and 0.8 cm 2 diameter, are at the end of the Description entered in a table as example 1.

Bei dem in den Figuren 2 und 3 ebenfalls nur teilweise dargestellten PTC-Widerstandselement ist die Elektrode 2 von einem starren, überwiegend plattenförmigen Metallkörper, beispielsweise aus Aluminium, Messing oder einem mit Nickel beschichteten Kupferkörper, gebildet. Im einem als Platte 6 ausgebildeten Teil des Metallkörpers sind mit Verbundstoff gefüllte Durchlässe 4 und/oder Vertiefungen 5 eingeformt. Die Vertiefungen 5 können zumindest zum Teil als Blindbohrungen ausgeführt sein, können aber auch gebildet werden durch eine aufgerauhte Oberfläche mit einer Oberflächenrauhigkeit, welche grösser ist als die mittlere Korngrösse des im Polymer enthaltenen Füllstoffs. Durch die Durchlässe 4 und Vertiefungen 5 wird eine gute Haftung und Verankerung des beispielsweise in einem Spritzpressverfahren angeformten Widerstandskörpers 1 am Metallkörper und somit ein geringer Übergangswiderstand zwischen Elektrode 2 und Widerstandskörper 1 erreicht. Die durch die unterschiedlichen Wärmeausdehnungskoeffizienten von Metall und Verbundstoff bei Temperaturbelastung entstehenden mechanischen Spannungen begünstigen eine feste Verankerung von Metall und Verbundstoff und tragen so zusätzlich zu einer Erhöhung der Kontaktkraft bzw. einer Reduktion des Übergangswiderstands bei. Der Metallkörper ist im allgemeinen als Platte ausgebildet. Er kann an die Platte angeformte Schenkel 7 aufweisen, welche einer zusätzlichen Verbesserung der Verankerung des Widerstandskörpers 1 dienen. Einer der Schenkel kann zudem zum Tragen des Stromanschlusses 3 vorgesehen sein.In the case of the PTC resistance element likewise only partially shown in FIGS. 2 and 3 the electrode 2 is of a rigid, predominantly plate-shaped metal body, for example made of aluminum, brass or a with nickel-coated copper body. In one as plate 6 formed part of the metal body are passages 4 filled with composite and / or depressions 5 are formed. The wells 5 can at least Part be designed as blind holes, but can also be formed by a roughened surface with a surface roughness that is greater than the average grain size of the filler contained in the polymer. Through the Passages 4 and recesses 5 will ensure good adhesion and anchoring of the for example, a resistance body 1 molded in an injection molding process on the metal body and thus a low contact resistance between the electrode 2 and resistance body 1 reached. The through the different Coefficient of thermal expansion of metal and composite Mechanical stresses that arise from thermal stress favor firm anchoring of metal and composite and thus contribute to one Increase in contact force or a reduction in contact resistance. The metal body is generally designed as a plate. He can hit the plate molded legs 7, which an additional improvement in Anchor the resistance body 1 serve. One of the legs can also be provided for carrying the power connection 3.

Sind die Vertiefungen auf eine geeignet bemessene Oberflächenrauhigkeit zurückzuführen, so wird eine besonders gute Haftung dann erreicht, wenn die Rauhigkeit grösser ist als die Abmessungen des grössten Füllstoffteilchens. Liegen die Korngrössen beispielsweise zwischen 10 und 40 µm, so empfiehlt es sich, die Oberflächenrauhigkeit dann grösser 40 bis 50 um zu wählen.Are the depressions on a suitably dimensioned surface roughness particularly good liability is achieved if the Roughness is larger than the dimensions of the largest filler particle. Lie the grain sizes between 10 and 40 microns, for example, it is recommended that Surface roughness then greater than 40 to 50 to choose.

Aus zwei Aluminium- bzw. Messingkörpern und einem mit 50 Volumenprozent Titandiborid gefüllten Polyäthylen wurden zwei entsprechend den Figuren 2 und 3 ausgeführte PTC-Widerstandselemente gefertigt. An diesen Widerstandselementen wurde bei Raumtemperatur (23°C) der Kontaktwiderstand Ro unmittelbar nach der Fertigung gemessen. An den gleichen Widerstandselementen wurde der Kontaktwiderstand Ro' nach zehn Behandlungszyklen, welche jeweils eine 24-stündige Einlagerung bei 60°C und Abkühlung auf Raumtemperatur umfassen, gemessen. Die Messwerte von Ro und Ro', der die Zunahme des Kontaktwiderstands des PTC-Widerstandselements beschreibenden Quotient Ro'/Ro und der relative Kontaktwiderstand in Prozent, bezogen auf einen Probewiderstand von 1 cm Länge und 0,8 cm2 Durchmesser, sind in der am Schluss der Beschreibung vorgesehenen Tabelle als Beispiele 2 und 3 eingetragen.Two PTC resistance elements designed in accordance with FIGS. 2 and 3 were produced from two aluminum or brass bodies and a polyethylene filled with 50 percent by volume titanium diboride. The contact resistance Ro was measured on these resistance elements at room temperature (23 ° C.) immediately after production. The contact resistance Ro 'was measured on the same resistance elements after ten treatment cycles, each comprising 24-hour storage at 60 ° C. and cooling to room temperature. The measured values of Ro and Ro ', the quotient Ro' / Ro describing the increase in the contact resistance of the PTC resistance element and the relative contact resistance in percent, based on a test resistance of 1 cm length and 0.8 cm 2 diameter, are in the am At the end of the description table provided as examples 2 and 3.

In einer weiteren Ausführungsform eines der PTC-Widerstandselemente nach der Erfindung wird die Elektrode von einem Verbundstoff gebildet mit einer Polymermatrix und einem in die Matrix eingebetteten pulverförmigen Füllstoff aus einem duktilen und eine hohe elektrische Leitfähigkeit aufweisenden Material. Elektrode 2 und Widerstandskörper 1 des erfindungsgemässen PTC-Widerstandselementes weisen bei dieser Ausführungsform praktisch die gleichen Wärmeausdehnungskoeffizenten auf. Mechanische Spannungen im PTC-Widerstandselement werden so bei Temperaturbelastung vermieden und es wird ein gutes Langzeitverhalten des Widerstandselementes auch nach wiederholtem Ausführen eines strombegrenzenden PTC-Überganges erreicht. Ein geeigneter Verbundstoff ist ein mit einem Pulver auf der Basis Silber, Gold und/oder Kupfer gefülltes Polymer, welches mit Vorteil das gleiche Polymer wie das im Verbundstoff des Widerstandskörpers vorgesehene, beispielsweise Polyäthylen, ist. An diesen elektrisch hervorragend leitenden Verbundstoff kann dann problemlos ein etwa als Druckkontakt ausgebildeter metallischer Stromanschluss angebracht werden.In a further embodiment, one of the PTC resistance elements according to the Invention is formed from a composite with an electrode Polymer matrix and a powdery filler embedded in the matrix a ductile and high electrical conductivity material. Electrode 2 and resistance body 1 of the PTC resistance element according to the invention have practically the same in this embodiment Coefficients of thermal expansion. Mechanical stresses in the PTC resistance element are thus avoided under temperature loads and it will good long-term behavior of the resistance element even after repeated Execution of a current-limiting PTC transition reached. A suitable one Composite is one with a powder based on silver, gold and / or copper filled polymer, which is advantageously the same polymer as that in the composite the resistance body provided, for example polyethylene. On this electrically excellent conductive composite can then easily be used as a Pressure contact trained metallic power connector can be attached.

Aus einem mit 50 Volumenprozent Silberpulver gefüllten Polyäthylen und einem mit 50 Volumenprozent Titandiboridpulver gefüllten Polyäthylen wurde ein PTC-Widerstandselement mit einem Widerstandskörper aus einem titandiboridhalten Polyäthylen und zwei Silber-Polyäthylen-Verbundstoffelektroden gefertigt. Dieses PTC-Widerstandselement wurde mit zwei Druckkontakten versehen und es wurde bei Raumtemperatur (23°C) der Kontaktwiderstand Ro unmittelbar nach der Fertigung gemessen. Am gleichen Widerstandselement wurde der Kontaktwiderstand Ro' nach zehn Behandlungszyklen, welche jeweils eine 24-stündige Einlagerung bei 60°C und Abkühlung auf Raumtemperatur umfassen, und nach dem Anlegen der Druckkontakte gemessen. Die Messwerte von Ro und Ro', der die Zunahme des Kontaktwiderstands des PTC-Widerstandselements beschreibenden Quotient Ro'/Ro und der relative Kontaktwiderstand in Prozent, bezogen auf einen Probewiderstand von 1 cm Länge und 0,8 cm2 Durchmesser, sind in der nachfolgenden Tabelle als Beispiel 4 eingetragen. Zugleich sind in der Tabelle auch ein Vergleichsbeispiel I eingetragen, bei dem die Druckkontakte unmittelbar auf den titandiboridhaltigen Widerstandskörper gepresst wurden, und ein Vergleichsbeispiel II, bei dem als zwei jeweils als Elektrode verwendete Nickelfolien in den Widerstandskörper eingebettet wurden. Beispiel Ro [mΩ] Ro' [mΩ] Ro'/Ro Relativer Wert des Kontaktwiderstands in % 1 (Nickelschaum) 337 394 1.17 10 2 (Aluminiumelektrode) 425 475 1.12 10 3 (Messingelektrode) 148 168 1.14 10 4(Ag-PE-Elektrode) 15 17 1.12 6 Vergleichsprobe I (Druckkontakt) 285 354 1.24 20 Vergleichsprobe II (Ni-Folie) 307 427 1.39 5 A PTC resistance element with a resistance body made of a titanium-containing polyethylene and two silver-polyethylene composite electrodes was produced from a polyethylene filled with 50 volume percent silver powder and a polyethylene filled with 50 volume percent titanium diboride powder. This PTC resistance element was provided with two pressure contacts and the contact resistance Ro was measured immediately after manufacture at room temperature (23 ° C.). The contact resistance Ro 'was measured on the same resistance element after ten treatment cycles, each comprising 24-hour storage at 60 ° C. and cooling to room temperature, and after the pressure contacts had been applied. The measured values of Ro and Ro ', the quotient Ro' / Ro describing the increase in the contact resistance of the PTC resistance element and the relative contact resistance in percent, based on a test resistance of 1 cm in length and 0.8 cm 2 in diameter, are as follows Table entered as example 4. At the same time, a comparative example I in which the pressure contacts were pressed directly onto the titanium diboride-containing resistor body and a comparative example II in which two nickel foils used as electrodes were embedded in the resistor body are also entered in the table. example Ro [mΩ] Ro '[mΩ] Ro '/ ro Relative value of contact resistance in% 1 (nickel foam) 337 394 1.17 10 2 (aluminum electrode) 425 475 1.12 10 3 (brass electrode) 148 168 1.14 10 4 (Ag-PE electrode) 15 17 1.12 6 Comparative sample I (pressure contact) 285 354 1.24 20 Comparative sample II (Ni foil) 307 427 1:39 5

Aus dieser Tabelle ist ersichtlich, dass sich bei allen erfindungsgemäss ausgeführten PTC-Widerstandselementen der Kontaktwiderstand Ro' auch nach zehn (einem längeren Betriebseinsatz entsprechenden) Behandlungszyklen gegenüber dem Kontaktwiderstand Ro vor dem Betriebseinsatz nicht nennenswert erhöht hat, so dass diese Widerstandselemente auch nach längerem Betriebseinsatz praktisch noch vollumfänglich funktionstüchtig sind.From this table it can be seen that in accordance with the invention executed PTC resistance elements the contact resistance Ro 'also after ten treatment cycles (corresponding to a longer period of use) not noteworthy compared to the contact resistance Ro before use has increased, so that these resistance elements even after a long time Operational use are still fully functional.

Anstelle einer Elektrode aus einem Verbundstoff auf der Basis duktiles Metall und Polyäthylen kann die Elektrode auch von einem Verbundstoff gebildet werden, welcher eine Polymermatrix enthält, die einen höheren Schmelzpunkt aufweist als die Polymermatrix des Widerstandskörpers, und einen in die Matrix eingebetteten pulverförmigen Füllstoff aus einer elektrisch leitfähigen Keramik oder einem Metall geringer Duktilität. Diese Elektrode führt bei einer höheren Temperatur als der Widerstandskörper einen PTC-Übergang aus. Wird eine Stelle des Widerstandskörper beim Strombegrenzen lokal überhitzt und kann der Strom über diese lokale Stelle weiterhin fliessen, so löst die Überhitzung zeitverzögert in der Elektrode einen zweiten PTC-Übergang aus, welcher den Strom begrenzt und so ein Versagen des PTC-Widerstandselements verhindert.Instead of an electrode made of a composite based on ductile metal and In polyethylene, the electrode can also be formed from a composite, which contains a polymer matrix that has a higher melting point than the polymer matrix of the resistance body, and one embedded in the matrix powdered filler made of an electrically conductive ceramic or a metal low ductility. This electrode leads at a higher temperature than that Resistor body from a PTC transition. Will a place of Resistor body locally overheats when limiting the current and the current can over this local point continues to flow, the overheating is triggered with a time delay in the Electrode a second PTC transition, which limits the current and so prevents failure of the PTC resistance element.

BEZUGSZEICHENLISTELIST OF REFERENCE NUMBERS

11
Widerstandskörperresistance body
22
Elektrodeelectrode
33
Stromanschlusspower connection
44
Durchlässepassages
55
Vertiefungenwells
66
Platteplate
77
Schenkelleg

Claims (8)

Widerstandselement mit einem Widerstandskörper (1) aus einem PTC-Verhalten aufweisenden Verbundstoff auf der Basis eines füllstoffenthaltenden Polymers und mit zwei den Widerstandskörper elektrisch kontaktierenden Elektroden (2), dadurch gekennzeichnet, dass mindestens eine der Elektroden (2) einen flexiblen Metallschaum enthält.Resistance element with a resistance body (1) made of a composite with PTC behavior based on a filler-containing polymer and with two electrodes (2) electrically contacting the resistance body, characterized in that at least one of the electrodes (2) contains a flexible metal foam. Widerstandselement nach Anspruch 1, dadurch gekennzeichnet, dass zumindest ein Teil des Metallschaums mit Verbundstoff gefüllte, offene Poren aufweist.Resistance element according to claim 1, characterized in that at least part of the metal foam has open pores filled with composite. Widerstandselement mit einem Widerstandskörper aus einem PTC-Verhalten aufweisenden Verbundstoff auf der Basis eines füllstoffenthaltenden Polymers und mit zwei den Widerstandskörper elektrisch kontaktierenden Elektroden, von denen mindestens eine (2) als starrer Metallkörper ausgebildet ist, dadurch gekennzeichnet, dass der Metallkörper mit Verbundstoff gefüllte Vertiefungen (5) und/oder Durchlässe (4) aufweist.Resistance element with a resistance body made of a composite with PTC behavior based on a filler-containing polymer and with two electrodes electrically contacting the resistance body, of which at least one (2) is designed as a rigid metal body, characterized in that the metal body has depressions filled with composite ( 5) and / or passages (4). Widerstandselement nach Anspruch 3, dadurch gekennzeichnet, dass zumindest ein Teil der Vertiefungen (5) als Blindbohrungen ausgebildet ist.Resistance element according to claim 3, characterized in that at least part of the recesses (5) is designed as blind bores. Widerstandselement nach Anspruch 3 oder 4, dadurch gekennzeichnet, dass die Vertiefungen von einer aufgerauhten Oberfläche gebildet werden mit einer Oberflächenrauhigkeit, welcher grösser ist als die mittlere Korngrösse des im Polymer enthaltenen Füllstoffs.Resistance element according to claim 3 or 4, characterized in that the depressions are formed by a roughened surface with a surface roughness which is greater than the average grain size of the filler contained in the polymer. Widerstandselement nach Anspruch 5, dadurch gekennzeichnet, dass die Oberflächenrauhigkeit grösser ist als Korngrösse des grössten Füllstoffteilchens. Resistance element according to claim 5, characterized in that the surface roughness is greater than the grain size of the largest filler particle. Widerstandselement mit einem Widerstandskörper aus einem PTC-Verhalten aufweisenden Verbundstoff auf der Basis eines füllstoffenthaltenden Polymers und mit zwei den Widerstandskörper elektrisch kontaktierenden Elektroden, dadurch gekennzeichnet, dass mindestens eine der beiden Elektroden von einem Verbundstoff gebildet ist mit einer Polymermatrix und einem in die Matrix eingebetteten pulverförmigen Füllstoff aus einem duktilen, elektrisch leitfähigen Material oder aus einem Verbundstoff mit einer Polymermatrix, die einen höheren Schmelzpunkt aufweist als die Polymermatrix des Verbundstoffs, und einem in die Matrix eingebetteten pulverförmigen Füllstoff aus einer elektrisch leitfähigen Keramik oder einem Metall geringer Duktilität.Resistance element with a resistance body made of a composite having PTC behavior on the basis of a filler-containing polymer and with two electrodes electrically contacting the resistance body, characterized in that at least one of the two electrodes is formed by a composite with a polymer matrix and a powdery one embedded in the matrix Filler made of a ductile, electrically conductive material or of a composite with a polymer matrix that has a higher melting point than the polymer matrix of the composite, and a powdery filler embedded in the matrix made of an electrically conductive ceramic or a metal of low ductility. Widerstandselement nach Anspruch 7, dadurch gekennzeichnet, dass das duktile Material des Füllstoffs Silber, Gold und/oder Kupfer enthält.Resistance element according to claim 7, characterized in that the ductile material of the filler contains silver, gold and / or copper.
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