EP0696036A1 - Process for the preparation of a PTC resistance and resistance obtained therefrom - Google Patents
Process for the preparation of a PTC resistance and resistance obtained therefrom Download PDFInfo
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- EP0696036A1 EP0696036A1 EP95810464A EP95810464A EP0696036A1 EP 0696036 A1 EP0696036 A1 EP 0696036A1 EP 95810464 A EP95810464 A EP 95810464A EP 95810464 A EP95810464 A EP 95810464A EP 0696036 A1 EP0696036 A1 EP 0696036A1
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- 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
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- the invention is based on a method for producing a PTC resistor according to the introductory part of patent claim 1.
- the invention also relates to a PTC resistor produced by this method and a particularly preferred use of this PTC resistor.
- a method for producing a resistor with PTC behavior is described, for example, in WO-A-9119297.
- powdery material based on a polyolefin such as in particular polyethylene, polypropylene or polybutene, or any linear polymer, such as polyamide, polyethylene terephthalate, polybutene terephthalate or polyoxymethylene, with powdery conductive material such as carbon black, a pure metal such as nickel, Tungsten, molybdenum, cobalt, copper, silver or aluminum, an alloy such as brass, a boride such as ZrB2 or TiB2, a carbide such as TaC, WC or ZrC, a nitride such as ZrN or TiO, or an oxide such as V2O3 or TiO, mixed.
- the polymer takes up at least 30 and the electrically conductive material at least 20 percent by volume of the resulting mixture.
- a plate is formed from the mixture, which is pressed together with electrodes attached to it at elevated temperature
- the temperature is set in such a way that the polymer melts at least on the grain surfaces and thus the plate is compacted into a compact body carrying electrodes.
- This body has a specific electrical cold resistance of typically 30 to 50 m ⁇ ⁇ cm and undergoes a PTC transition at elevated temperatures, for example above 80 ° C.
- the specific electrical resistance increases by many orders of magnitude. This process is particularly suitable for the production of PTC resistors based on thermoplastic polymers.
- thermoset polymer A method for producing PTC resistors based on a thermoset polymer is described in T.R. Shrout et al. "Composite PTCR thermistors utilizing conducting borides, silicides, and carbides" J. of Material Science 26 (1991) 145-154.
- Epoxy resin and fillers based on electrically conductive borides, such as titanium, niobium or zirconium boride, carbides, such as titanium carbide, or silicides, such as niobium, tungsten or molybdenum silicide, are mixed at room temperature and the resulting mixture is poured into molds and cured to resistance bodies at approx. 80 ° C. The resistance bodies are then polished and provided with electrodes.
- Resistance bodies based on an epoxy resin sold by Polysciences Inc. under the trade name Spurrs and the aforementioned borides, carbides or silicides have cold resistances of more than 5 ⁇ ⁇ cm at room temperature, depending on the type and proportion of the filler.
- the invention has for its object to provide a method of the type mentioned, with the help of which it is possible in a simple and safe manner, regardless of the type of polymer used, PTC resistors with very low cold resistance and large nominal current carrying capacity.
- the method according to the invention is characterized by method steps which are easy to carry out with common means and are easy to control. Appropriate selection and treatment of polymer and filler not only significantly reduce the specific cold resistance of the PTC resistor produced by the method according to the invention compared to comparable sized resistors according to the prior art, but at the same time a high PTC transition temperature of this resistor is ensured. A high PTC transition temperature enables a higher working temperature of the resistor.
- the resistor produced by the method according to the invention can be loaded with comparatively high nominal currents without being heated to an unacceptably high level.
- the PTC resistor produced by the method according to the invention is therefore particularly interesting for power applications and can be used with great advantage as a component with a specific cold resistance of less than 25 m ⁇ ⁇ cm and / or with a high current carrying capacity at temperatures above 100 ° C. This is particularly the case if the resistance stroke, i.e. the ratio of its ohmic resistance R hot after the PTC transition to its ohmic resistance R cold at room temperature, at least 108, in suitable cases even if the combination of polymer and filler and after carrying out suitable heat treatment steps Is 1010 to 101. Particularly high electrical field strengths can then be maintained in the hot state. Amorphous polymers such as duromers based on epoxy are particularly suitable for this.
- PTC resistors are characterized by an extremely low cold resistance.
- the epoxy shrinks and builds up internal tensions, through which the individual filler particles are pressed against each other while reducing their contact resistances.
- hard filler particles it is also achieved that when the resistance heats up to the PTC transition, the individual filler particles are quickly separated from one another as a result of the expanding polymer matrix, thus reliably preventing the particles from sticking, as is possible with comparatively soft fillers becomes.
- Amorphous polymers such as epoxides in particular, have proven particularly useful in the manufacture of PTC resistors for power applications. This is mainly because compared to a PTC resistor based on a thermoplastic, a PTC resistor based on epoxy generally has a significantly lower specific cold resistance. The epoxy shrinks when it hardens and builds up internal tension. The conductive particles of the filler are pressed against each other and can, under certain conditions, reduce the contact resistance between neighboring particles considerably. An important prerequisite here is that the individual particles are sufficiently hard and separate from one another when the polymer matrix expands due to strong heating of the resistance, for example when a short-circuit current occurs.
- thermoplastics are also suitable as a polymer.
- thermoplastics with a large crystalline fraction can be used, such as polypropylene (PP) with a melting temperature (T m ) of approx.
- thermoplastic polyurethanes TPU; T m ⁇ 120-200 ° C), polybutylene terephthalate (PBT; T m ⁇ 120-200 ° C), polyethylene terephthalate (PET; T m ⁇ 255 ° C), polyethylene naphthalate (PEN; T m ⁇ 262 ° C), polyphenylene sulfide (PPS; T m ⁇ 288 ° C), syndiotactic polystyrene (s- PS; T m ⁇ 263 ° C), polyether ether ketone (PEEK; T m ⁇ 334 ° C), polyaryl ether ketone (PAEK; T m ⁇ 380 ° C), polybenzamide azole (PBI; T m ⁇ 700 ° C), fluoroplastics ( T m to 330 ° C), thermoplastic polyimide (TPI; T m ⁇ 406 ° C) or copoly
- the resulting materials are hot pressed in a mold or molded in an injection molding process.
- the materials are post-annealed below the melting temperature.
- particularly high dimensional stability can be achieved through thermal, chemical or radiation crosslinking.
- Particularly suitable fillers - alone or in a mixture - are typically metal borides, such as TiB2 or ZrB2, metal carbides, such as TiC or VC, metal nitrides, such as TiN, metal oxides, such as RuO2, and / or metal silicides, such as MoSi2 or WSi2 and / or a metal, such as in particular Mo, Ni and / or W.
- the fillers can have solid and / or hollow particles.
- particles of core-shell structure the shell made of one of the aforementioned borides, carbides, nitrides, oxides or silicides and the core made of a practically unalloyed metal, such as Ni, W, Ti, Zr, Mo, Co or Al, an alloy such as brass, or an oxide based on Ti or V, such as in particular TiO, V2O3 or VO, is formed.
- a practically unalloyed metal such as Ni, W, Ti, Zr, Mo, Co or Al
- an alloy such as brass
- an oxide based on Ti or V such as in particular TiO, V2O3 or VO
- a PTC resistor is shown with a arranged between two connection electrodes e1, e2 resistor body w.
- This resistance body w is made of a material with a comparatively low specific cold resistance of typically a few m ⁇ .cm and has a comparatively large length in the centimeter range in relation to its cross-sectional area of, for example, a few square centimeters. Its resistance stroke is greater than 108 and is typically 1010-101 ⁇ .
- the properties mentioned favor its use for power applications in the kV voltage range because, despite its long length, it can still carry a relatively high current density under continuous load and because it can easily withstand high voltages after the PTC transition in the high-resistance state.
- the resistance body w has a high PTC transition temperature of typically more than 130 ° C. This enables a higher working temperature of the resistor. Since the cooling of the resistance caused by free or forced convection is proportional to the difference between the working temperature and the ambient temperature, and since the cooling caused by radiation is even proportional to the fourth power of the working temperature, it can Resistor can be loaded with comparatively high nominal currents without it being heated to an unacceptably high level.
- electrically conductive, powdery fillers which were previously stored and / or chemically etched under vacuum or under a non-oxidizing atmosphere, in particular under a protective gas such as nitrogen or argon, were placed in a mixer were mixed homogeneously with liquid resins based on epoxy. In order to avoid sedimentation during the subsequent processing, the resin was gelled at an elevated temperature, for example 50-80 ° C. After adding a hardener, preferably based on diciandiamide or anhydride, the resulting mixture was poured into a mold or processed by injection molding and cured at temperatures between 120 and 220 ° C. to form the resistance bodies w.
- the electrodes e 1, e 2 were generally evaporated or glued onto the polished end faces of the resistance bodies after hardening, but some were already installed in the resistor during casting and subsequent hardening.
- powdery, electrically conductive fillers which were previously stored and / or chemically etched under vacuum or under a non-oxidizing atmosphere, in particular protective gas, such as nitrogen or argon, were mixed with powdery thermoplastics. The resulting mixtures were filled into molds together with the electrodes and pressed into the resistors at elevated temperature.
- the starting materials used, the temperature conditions when curing the epoxies, the temperature and pressure conditions when pressing the thermoplastics and the physical properties of the PTC resistors produced by the process according to the invention, such as PTC transition temperature, glass transition temperature and specific electrical cold resistance, can be seen from the following two tables and from Figures 2 to 5 and 7.
- the PTC transition temperatures of the PTC resistors produced by the method according to the invention can in some cases be increased considerably by suitable heat treatment. Resistors treated in this way can be operated at higher working temperatures and therefore have a higher rated current carrying capacity than resistors that have not been heat-treated.
- a suitable heat treatment is generally curing for several hours or post-curing at a temperature which is higher than the usual curing temperature (Examples 3, 5, 8, 14) (Examples 4, 7, 9), but can also be carried out in post-curing for several hours at a comparatively low temperature exist (Example 6). With a suitable choice of epoxy, PTC transition temperatures T c of up to 200 ° C.
- the specific cold resistance rho of the heat-treated resistors often significantly exceeds that of untreated resistors. Since the specific resistance is less than 1 ⁇ ⁇ cm even at temperatures up to 150 ° C, suitably manufactured resistors (examples 4, 6, 7) can be used for rated current supply in devices in which temperatures of 100 to 150 ° C occur over long periods .
- PTC transition temperatures can be achieved with certain thermoplastic polymers. From the tables and Figures 5 and 7 it can be seen that with polyphenylene sulfide (PPS) or syndiotactic polystyrene (s-PS) as a polymer and TiB2 as a filler PTC transition temperatures of at least 250 ° C can be achieved. Since the resistivity of a resistor made from such a material is less than 1 ⁇ ⁇ cm even at temperatures of 190-220 ° C., such a resistor can carry a relatively high nominal current. By means of suitable heat treatment (example 11), the specific resistance between 180 and 270 ° C. is for the most part very considerably reduced, as a result of which the nominal current carrying capacity at the high temperatures mentioned is significantly increased compared to a non-heat-treated resistor.
- PPS polyphenylene sulfide
- s-PS syndiotactic polystyrene
- the current carrying capacity of a PTC resistor made according to the invention made of PPS and TiB2 (example 10) of approximately cuboid shape (length approx. 20 mm, cross section approx. 30 mm) was made with a prior art PTC resistor made of PE and TiB2 (example 15) compared with corresponding dimensions.
- the current value was determined at which there was just no PTC transition. This resulted in a current density of approximately 120 A / cm for the resistor according to the invention, but only a current density of approximately 50 A / cm for the resistor according to the prior art.
- the average diameter of the particles of the filler should expediently be greater than 10 ⁇ m, since on the one hand good electrical cold conductivity is achieved.
- Fig. 6 in which the specific electrical cold resistance rho (at approx. 30 ° C) of four PTC resistors I (based on polyethylene and 50 vol% TiB2), II (based on polyethylene and 35 vol% TiB2), III (based on epoxy Spurr R and 35% by volume TiB2) and IV (based on polyethylene and 60% by volume TiB2 according to Example 18) depending on the size ps of the filler particles. If the particles are larger than 60 ⁇ m or 100 ⁇ m, particularly good electrical cold conductivity is achieved.
- the size of the filler particles to 500 microns, preferably even to 200 microns.
- the filler particles can be present in the form of fractions with typical mean particle diameters between 100 ⁇ m and 200 ⁇ m or 63 ⁇ m and 100 ⁇ m or optionally also between 32 ⁇ m and 45 ⁇ m or 10 and 32 ⁇ m.
- a relatively small specific cold resistance is also achieved if the filler has a relatively large volume fraction of coarse particles with average diameters of, for example, 63 ⁇ m to 100 ⁇ m and a relatively small volume fraction of fine particles with diameters of up to 10 ⁇ m, for example.
Abstract
Description
Bei der Erfindung wird ausgegangen von einem Verfahren zur Herstellung eines PTC-Widerstandes nach dem einleitenden Teil von Patentanspruch 1. Die Erfindung betrifft auch einen nach diesem Verfahren hergestellten PTC-Widerstand sowie eine besonders bevorzugte Verwendung dieses PTC-Widerstandes.The invention is based on a method for producing a PTC resistor according to the introductory part of
Ein Verfahren zur Herstellung eines Widerstands mit PTC-Verhalten ist beispielsweise in WO-A-9119297 beschrieben. Bei diesem Verfahren wird pulverförmiges Material auf der Basis eines Polyolefins, wie insbesondere Polyäthylen, Polypropylen oder Polybuten, oder irgendeinanderes lineares Polymer, wie etwa Polyamid, Polyäthylenterephtalat, Polybutenterephtalat oder Polyoxymethylen, mit pulverförmigem leitendem Material, wie Russ, einem reinen Metall, wie Nickel, Wolfram, Molybdän, Cobalt, Kupfer, Silber oder Aluminium, einer Legierung, wie Messing, einem Borid, wie ZrB₂ oder TiB₂, einem Carbid, wie TaC, WC oder ZrC, einem Nitrid, wie ZrN oder TiO, oder einem Oxid, wie V₂O₃ oder TiO, vermischt. Das Polymer nimmt hierbei mindestens 30 und das elektrisch leitfähige Material mindestens 20 Volumenprozent der sich ergebenden Mischung ein. Aus der Mischung wird eine Platte geformt, welche zusammen mit daran angebrachten Elektroden bei erhöhter Temperatur verpresst wird.A method for producing a resistor with PTC behavior is described, for example, in WO-A-9119297. In this process, powdery material based on a polyolefin, such as in particular polyethylene, polypropylene or polybutene, or any linear polymer, such as polyamide, polyethylene terephthalate, polybutene terephthalate or polyoxymethylene, with powdery conductive material such as carbon black, a pure metal such as nickel, Tungsten, molybdenum, cobalt, copper, silver or aluminum, an alloy such as brass, a boride such as ZrB₂ or TiB₂, a carbide such as TaC, WC or ZrC, a nitride such as ZrN or TiO, or an oxide such as V₂O₃ or TiO, mixed. The polymer takes up at least 30 and the electrically conductive material at least 20 percent by volume of the resulting mixture. A plate is formed from the mixture, which is pressed together with electrodes attached to it at elevated temperature.
Die Temperatur ist hierbei so eingestellt, dass das Polymer zumindest an den Kornoberflächen schmilzt und so die Platte zu einem kompakten, Elektroden tragenden Körper verdichtet wird. Dieser Körper weist einen spezifischen elektrischen Kaltwiderstand von typischerweise 30 bis 50 mΩ·cm auf und durchläuft bei erhöhten Temperaturen, beispielsweise oberhalb 80°C, einen PTC-Übergang. Der spezifische elektrische Widerstand erhöht sich dabei um viele Grössenordnungen. Dieses Verfahren ist vor allem zur Herstellung von PTC-Widerständen auf der Basis von thermoplastischen Polymeren geeignet.The temperature is set in such a way that the polymer melts at least on the grain surfaces and thus the plate is compacted into a compact body carrying electrodes. This body has a specific electrical cold resistance of typically 30 to 50 mΩ · cm and undergoes a PTC transition at elevated temperatures, for example above 80 ° C. The specific electrical resistance increases by many orders of magnitude. This process is particularly suitable for the production of PTC resistors based on thermoplastic polymers.
Ein Verfahren zur Herstellung von PTC-Widerständen auf der Basis eines duromeren Polymers ist beschrieben in T.R.Shrout et al. "Composite PTCR thermistors utilizing conducting borides, silicides, and carbides" J. of Material Science 26(1991) 145-154. Hierbei werden Epoxidharz und Füllstoffe auf der Basis von elektrisch leitfähigen Boriden, wie Titan-, Niob- oder Zirkoniumborid, Carbiden, wie Titancarbid, oder Siliciden, wie Niob-, Wolfram- oder Molybdänsilicid, bei Zimmertemperatur vermischt und die resultierende Mischung in Formen abgegossen und bei ca. 80°C zu Widerstandskörpern ausgehärtet. Die Widerstandskörper werden sodann poliert und mit Elektroden versehen. Widerstandskörper auf der Basis eines von der Fa. Polysciences Inc. unter der Handelsbezeichnung Spurrs vertriebenen Epoxidharzes und der vorgenannten Boride, Carbide oder Silicide weisen je nach Art und Anteil des Füllstoffs bei Zimmertemperatur Kaltwiderstände von mehr als 5 Ω·cm auf.A method for producing PTC resistors based on a thermoset polymer is described in T.R. Shrout et al. "Composite PTCR thermistors utilizing conducting borides, silicides, and carbides" J. of Material Science 26 (1991) 145-154. Epoxy resin and fillers based on electrically conductive borides, such as titanium, niobium or zirconium boride, carbides, such as titanium carbide, or silicides, such as niobium, tungsten or molybdenum silicide, are mixed at room temperature and the resulting mixture is poured into molds and cured to resistance bodies at approx. 80 ° C. The resistance bodies are then polished and provided with electrodes. Resistance bodies based on an epoxy resin sold by Polysciences Inc. under the trade name Spurrs and the aforementioned borides, carbides or silicides have cold resistances of more than 5 Ω · cm at room temperature, depending on the type and proportion of the filler.
Der Erfindung, wie sie in Patentanspruch 1 angegeben ist, liegt die Aufgabe zugrunde, ein Verfahren der eingangs genannten Art anzugeben, mit dessen Hilfe es in einfacher und sicherer Weise gelingt, unabhängig von der Art des verwendeten Polymers PTC-Widerstände mit sehr geringem Kaltwiderstand und grosser Nennstromtragfähigkeit herzustellen.The invention, as specified in
Das erfindungsgemässe Verfahren zeichnet sich durch Verfahrensschritte aus, welche mit geläufigen Mitteln leicht durchzuführen und einfach zu kontrollieren sind. Durch geeignete Auswahl und Behandlung von Polymer und Füllstoff wird nicht nur der spezifische Kaltwiderstand des nach dem erfindungsgemässen Verfahren hergestellten PTC-Widerstands gegenüber vergleichbar bemessenen Widerständen nach dem Stand der Technik erheblich herabgesetzt, zugleich ist auch eine hohe PTC-Übergangstemperatur dieses Widerstands gewährleistet. Eine hohe PTC-Übergangstemperatur ermöglicht eine höhere Arbeitstemperatur des Widerstands. Da die durch freie oder erzwungene Konvektion bedingte Kühlung des Widerstands proportional der Differenz zwischen Arbeitstemperatur und der Umgebungstemperatur ist, und da die durch Abstrahlung bedingte Kühlung sogar proportional der vierten Potenz der Arbeitstemperatur ist, kann der nach dem erfindungsgemässen Verfahren hergestellte Widerstand mit vergleichsweise hohen Nennströmen belastet werden, ohne dass er unzulässig hoch erwärmt wird.The method according to the invention is characterized by method steps which are easy to carry out with common means and are easy to control. Appropriate selection and treatment of polymer and filler not only significantly reduce the specific cold resistance of the PTC resistor produced by the method according to the invention compared to comparable sized resistors according to the prior art, but at the same time a high PTC transition temperature of this resistor is ensured. A high PTC transition temperature enables a higher working temperature of the resistor. Since the cooling of the resistor caused by free or forced convection is proportional to the difference between the working temperature and the ambient temperature, and since the cooling caused by radiation is even proportional to the fourth power of the working temperature, the resistor produced by the method according to the invention can be loaded with comparatively high nominal currents without being heated to an unacceptably high level.
Der nach dem erfindungsgemässen Verfahren hergestellte PTC-Widerstand ist daher besonders interessant für Leistungsanwendungen und kann mit grossem Vorteil als Bauelement mit einem spezifischen Kaltwiderstand kleiner 25 mΩ·cm und/oder mit einer hohen Stromtragfähigkeit bei Temperaturen oberhalb 100°C verwendet werden. Dies insbesondere dann, wenn durch geeignete Kombination von Polymer und Füllstoff sowie nach Durchführung geeigneter Wärmebehandlungsschritte der Widerstandshub, das heisst das Verhältnis seines ohmschen Widerstandes Rheiss nach dem PTC-Übergang zu seinem ohmschen Widerstand Rkalt bei Raumtemperatur, mindestens 10⁸, in geeigneten Fällen sogar 10¹⁰ bis 10¹ beträgt. Es können dann im heissen Zustand besonders hohe elektrische Feldstärken gehalten werden. Hierfür besonders geeignet sind insbesondere amorphe Polymere, wie Duromere auf der Basis von Epoxid. Solche PTC-Widerstände zeichnen sich bei geeigneter Materialauswahl und Behandlung durch einen äusserst geringen Kaltwiderstand aus. Beim Aushärten schrumpft das Epoxid und baut innere Spannungen auf, durch welche die einzelnen Füllstoffteilchen unter gleichzeitiger Reduktion ihrer Kontaktwiderstände gegeneinander gepresst werden. Durch Auswahl harter Füllstoffteilchen wird zugleich erreicht, dass bei dem zum PTC-Übergang führenden Erwärmen des Widerstands die einzelnen Füllstoffteilchen infolge der sich dehnenden Polymermatrix rasch voneinander getrennt werden und somit ein Verkleben der Teilchen, wie dies bei vergleichsweise weichen Füllstoffen möglich ist, mit Sicherheit vermieden wird.The PTC resistor produced by the method according to the invention is therefore particularly interesting for power applications and can be used with great advantage as a component with a specific cold resistance of less than 25 mΩ · cm and / or with a high current carrying capacity at temperatures above 100 ° C. This is particularly the case if the resistance stroke, i.e. the ratio of its ohmic resistance R hot after the PTC transition to its ohmic resistance R cold at room temperature, at least 10⁸, in suitable cases even if the combination of polymer and filler and after carrying out suitable heat treatment steps Is 10¹⁰ to 10¹. Particularly high electrical field strengths can then be maintained in the hot state. Amorphous polymers such as duromers based on epoxy are particularly suitable for this. With suitable material selection and treatment, such PTC resistors are characterized by an extremely low cold resistance. When hardening, the epoxy shrinks and builds up internal tensions, through which the individual filler particles are pressed against each other while reducing their contact resistances. By selecting hard filler particles, it is also achieved that when the resistance heats up to the PTC transition, the individual filler particles are quickly separated from one another as a result of the expanding polymer matrix, thus reliably preventing the particles from sticking, as is possible with comparatively soft fillers becomes.
Das erfindungsgemässe Verfahren lässt sich im allgemeinen dann in vorteilhafter Weise ausführen, wenn folgende Voraussetzungen erfüllt sind:
- Wahl eines verglichen mit üblicherweise verwendeten Materialien, wie Silber und/oder Russ, harten Füllstoffs,
- Wahl eines Füllstoffs, der nur schwer ein isolierendes oxid bildet,
- Herstellung und Lagerung des Füllstoffs unter Schutzgas,
- Entfernen einer gegebenenfalls vorhandenen Oxidhaut durch chemisches Ätzen,
- Wahl von Füllstoffteilchen mit mittleren Durchmessern vorzugsweise grösser 10 µm,
- Wahl des Füllstoffgehalts vorzugsweise grösser 30 Vol%, und
- Wahl eines Epoxidharzes mit einer hohen Glasübergangstemperatur, vorzugsweise grösser 130°C, oder eines Thermoplasten mit einer hohen Schmelztemperatur, welche vorzugsweise grösser 140°C ist, oder eines thermoplastischen Elastomers, das vorzugsweise bei Temperaturen grösser 140°C vernetzt wird, oder eines Copolymeren, das wie beispielsweise Polyurethan-Copolymere ein sich durchdringendes Netzwerk, ein sogenanntes "Interpenetrating Network" (IPN) mit hoher, vorzugsweise oberhalb 140°C liegender, Schmelztemperatur bildet.
- Choice of a hard filler compared to commonly used materials such as silver and / or soot,
- Choosing a filler that is difficult to form an insulating oxide,
- Production and storage of the filler under protective gas,
- Removing any oxide skin that may be present by chemical etching,
- Choice of filler particles with average diameters, preferably larger than 10 µm,
- Choice of the filler content preferably greater than 30 vol%, and
- Choice of an epoxy resin with a high glass transition temperature, preferably greater than 130 ° C, or a thermoplastic with a high melting temperature, which is preferably greater than 140 ° C, or a thermoplastic elastomer, which is preferably crosslinked at temperatures greater than 140 ° C, or a copolymer, which, like for example polyurethane copolymers, forms an interpenetrating network (IPN) with a high melting temperature, preferably above 140 ° C.
Amorphe Polymer, wie insbesondere Epoxide, haben sich bei der Herstellung von PTC-Widerstände für Leistungsanwendungen besonders bewährt. Dies vor allem deswegen, da verglichen mit einem PTC-Widerstand auf der Basis eines Thermoplasts ein PTC-Widerstand auf der Basis von Epoxid im allgemeinen einen erheblich niedrigeren spezifischen Kaltwiderstand aufweist. Das Epoxid schrumpft nämlich beim Aushärten und baut dabei innere Spannungen auf. Hierbei werden die leitfähigen Teilchen des Füllstoffs aufeinander gepresst und können unter bestimmten Voraussetzungen den Kontaktwiderstand zwischen benachbarten Teilchen ganz erheblich reduzieren. Eine wichtige Voraussetzung ist hierbei, dass die einzelnen Teilchen ausreichend hart sind, und sich beim Expandieren der Polymermatrix infolge starker Erhitzung des Widerstandes, etwa beim Auftreten eines Kurzschlussstroms, voneinander trennen. Nur dann ist das Auftreten eines PTC-Überganges gewährleistet und wird ein Verkleben der Füllstoffteilchen, wie dies bei vergleichsweise weichem Material, wie etwa Silber möglich ist, mit Sicherheit vermieden. Als Polymere besonders bewährt haben sich amid-, insbesondere diciandiamid-, oder anhydridgehärtete Epoxide. Möglich ist auch die Zugabe eines oder mehrerer Katalysatoren. Solche Polymere weisen vergleichsweise hohe Glasübergangstemperaturen auf und verfügen zudem über einen thermischen Ausdehnungskoeffizienten grösser 10⁻⁵. Zusätzlich ist bei Duromeren oberhalb der PTC-Übergangstemperatur die Formstabilität des PTC-Widerstandes gewährleistet.Amorphous polymers, such as epoxides in particular, have proven particularly useful in the manufacture of PTC resistors for power applications. This is mainly because compared to a PTC resistor based on a thermoplastic, a PTC resistor based on epoxy generally has a significantly lower specific cold resistance. The epoxy shrinks when it hardens and builds up internal tension. The conductive particles of the filler are pressed against each other and can, under certain conditions, reduce the contact resistance between neighboring particles considerably. An important prerequisite here is that the individual particles are sufficiently hard and separate from one another when the polymer matrix expands due to strong heating of the resistance, for example when a short-circuit current occurs. Only then is the occurrence of a PTC transition guaranteed and does the filler particles stick together, as is possible with comparatively soft material, such as silver, for example. Amide-, in particular diciandiamide- or anhydride-hardened epoxides have proven particularly useful as polymers. It is also possible to add one or more catalysts. Such polymers have comparatively high glass transition temperatures and also have a thermal expansion coefficient greater than 10⁻⁵. In addition, the dimensional stability of the PTC resistor is guaranteed for thermosets above the PTC transition temperature.
Neben solchen Epoxiden sind auch Hochtemperatur-Thermoplaste als Polymer geeignet. Insbesondere Thermoplaste mit einem grossen kristallinen Anteil können verwendet werden, wie etwa Polypropylen (PP) mit einer Schmelztemperatur (Tm) von ca 165°C, thermoplastische Polyurethane (TPU; Tm≈120-200°C), Polybutylenterephtalat (PBT; Tm≈120-200°C), Polyäthylenterephtalat (PET; Tm≈255°C), Polyäthylennaphtalat (PEN; Tm≈262°C), Polyphenylensulfid (PPS; Tm≈288°C), Syndiotaktisches Polystyrol (s-PS; Tm≈263°C), Polyätherätherketon (PEEK; Tm≈334°C), Polyarylätherketon (PAEK; Tm≈380°C), Polybenzamid-azol (PBI; Tm≈700°C), Fluorkunststoffe (Tm bis 330°C), Thermoplastisches Polyimid (TPI; Tm≈406°C) oder Copolymere oder Mischungen davon.In addition to such epoxides, high-temperature thermoplastics are also suitable as a polymer. In particular thermoplastics with a large crystalline fraction can be used, such as polypropylene (PP) with a melting temperature (T m ) of approx. 165 ° C, thermoplastic polyurethanes (TPU; T m ≈120-200 ° C), polybutylene terephthalate (PBT; T m ≈120-200 ° C), polyethylene terephthalate (PET; T m ≈255 ° C), polyethylene naphthalate (PEN; T m ≈262 ° C), polyphenylene sulfide (PPS; T m ≈288 ° C), syndiotactic polystyrene (s- PS; T m ≈263 ° C), polyether ether ketone (PEEK; T m ≈334 ° C), polyaryl ether ketone (PAEK; T m ≈380 ° C), polybenzamide azole (PBI; T m ≈700 ° C), fluoroplastics ( T m to 330 ° C), thermoplastic polyimide (TPI; T m ≈406 ° C) or copolymers or mixtures thereof.
Bei der Verwendung eines Hochtemperatur-Thermoplasten, empfiehlt es sich, dass das erfindungsgemässe Verfahren einen der nachfolgend aufgelisteten Verfahrensschritte enthält:
- der Füllstoff wird mit einem Kneter in den heissen Thermoplasten eingemischt, oder
- der Füllstoff wird trocken mit Pulver aus dem thermoplastischen Material vermischt, oder
- thermoplastisches Material wird auf die Oberfläche der Füllstoffteilchen polymerisiert oder in einem Lösungsmittel gelöst mit dem Füllstoff vermischt und die Mischung anschliessend etwa durch Gefrieren oder Sprühen getrocknet.
- the filler is mixed into the hot thermoplastic with a kneader, or
- the filler is dry mixed with powder from the thermoplastic material, or
- Thermoplastic material is polymerized onto the surface of the filler particles or mixed with the filler dissolved in a solvent and the mixture is then dried, for example by freezing or spraying.
Die hieraus resultierenden Materialien werden in einer Form heissgepresst oder in einem Spritzgussverfahren geformt. Um einen erwünscht hohen Kristallinitätsgrad des Polymers zu erreichen, werden die Materialien unterhalb der Schmelztemperatur nachgetempert. Zusätzlich kann durch thermische, chemische oder Strahlenvernetzung eine besonders hohe Formstabilität erreicht werden.The resulting materials are hot pressed in a mold or molded in an injection molding process. In order to achieve a desired high degree of crystallinity of the polymer, the materials are post-annealed below the melting temperature. In addition, particularly high dimensional stability can be achieved through thermal, chemical or radiation crosslinking.
Besonders geeignete Füllstoffe - allein oder in Mischung - sind typischerweise Metallboride, wie TiB₂ oder ZrB₂, Metallcarbide, wie TiC oder VC, Metallnitride, wie TiN, Metalloxide, wie RuO₂, und/oder Metallsilizide, wie MoSi₂ oder WSi₂ und/oder ein Metall, wie insbesondere Mo, Ni und/oder W. Die Füllstoffe können massive und/oder hohle Teilchen aufweisen. Sie können aber auch Teilchen von Kern-Schale-Struktur aufweisen, wobei die Schale aus einem der vorgenannten Boride, Carbide, Nitride, Oxide oder Silizide und der Kern aus einem praktisch unlegierten Metall, wie Ni, W, Ti, Zr, Mo, Co oder Al, einer Legierung, wie Messing, oder einem Oxid auf der Basis von Ti oder V, wie insbesondere TiO, V₂O₃ oder VO, gebildet ist.Particularly suitable fillers - alone or in a mixture - are typically metal borides, such as TiB₂ or ZrB₂, metal carbides, such as TiC or VC, metal nitrides, such as TiN, metal oxides, such as RuO₂, and / or metal silicides, such as MoSi₂ or WSi₂ and / or a metal, such as in particular Mo, Ni and / or W. The fillers can have solid and / or hollow particles. But they can also have particles of core-shell structure, the shell made of one of the aforementioned borides, carbides, nitrides, oxides or silicides and the core made of a practically unalloyed metal, such as Ni, W, Ti, Zr, Mo, Co or Al, an alloy such as brass, or an oxide based on Ti or V, such as in particular TiO, V₂O₃ or VO, is formed.
Bevorzugte Ausführungsbeispiele der Erfindung und die damit erzielbaren weiteren Vorteile werden nachfolgend anhand von Zeichnungen näher erläutert.Preferred exemplary embodiments of the invention and the further advantages achievable therewith are explained in more detail below with reference to drawings.
In den Zeichnungen sind Ausführungsbeispiele der Erfindung vereinfacht dargestellt, und zwar zeigt die
- Fig. 1
- in perspektivischer Ansicht einen nach dem erfindungsgemässen Verfahren hergestellten PTC-Widerstand auf der Basis einer Polymermatrix und darin eingebetteter elektrisch leitender Füllstoffteilchen,
- Fig.2
- ein Diagramm, in dem der spezifische Widerstand [Ω·cm] eines nach dem erfindungsgemässen Verfahren hergestellten PTC-Widerstands (1) sowie von Vergleichswiderständen auf der Basis eines Epoxids (8) und eines Thermoplasts (15, 16) in Funktion der Temperatur [°C] dargestellt ist,
- Fig.3
- ein Diagramm, in dem der spezifische Widerstand [Ω·cm] von zwei nach dem erfindungsgemässen Verfahren hergestellten PTC-Widerständen (4, 9) sowie von drei Vergleichswiderständen (3, 8, 14) jeweils auf der Basis eines Epoxids in Funktion der Temperatur [°C] dargestellt ist,
- Fig.4
- ein Diagramm, in dem der spezifische Widerstand [Ω·cm] von drei nach dem erfindungsgemässen Verfahren hergestellten PTC-Widerständen (5, 6, 7), welche bei unterschiedlichen Verfahrensbedingungen hergestellt wurden, in Funktion der Temperatur [°C] dargestellt ist,
- Fig.5
- ein Diagramm, in dem der spezifische Widerstand rho [Ω·cm] von zwei nach dem erfindungsgemässen Verfahren hergestellten PTC-Widerständen (10, 11) auf der Basis eines thermoplastischen Polymers in Funktion der Temperatur [°C] dargestellt ist,
- Fig.6
- ein Diagramm, in dem der spezifischen Kaltwiderstand [mΩ·cm] von vier PTC-Widerstandsfamilien I, II, III, IV jeweils auf der Basis eines Epoxids oder Thermoplasts und mit jeweils gleichem Füllstoffanteil in Funktion vom mittleren Durchmesser der Füllstoffteilchen dargestellt ist, und
- Fig.7
- ein Diagramm, in dem der spezifische Widerstand [Ω·cm] eines PTC-Widerstands auf der Basis eines Hochtemperaturthermoplasts in Funktion der Temperatur [°C] dargestellt ist.
- Fig. 1
- a perspective view of a PTC resistor produced according to the inventive method based on a polymer matrix and electrically conductive filler particles embedded therein,
- Fig. 2
- a diagram in which the specific resistance [Ω · cm] of a PTC resistor (1) produced by the method according to the invention and of comparative resistors based on an epoxy (8) and a thermoplastic (15, 16) as a function of temperature [° C] is shown
- Fig. 3
- a diagram in which the specific resistance [Ω · cm] of two PTC resistors (4, 9) produced by the method according to the invention and of three comparison resistors (3, 8, 14) each based on an epoxy as a function of temperature [ ° C] is shown,
- Fig. 4
- 2 shows a diagram in which the specific resistance [Ω · cm] of three PTC resistors (5, 6, 7) produced by the method according to the invention, which were produced under different process conditions, is shown as a function of the temperature [° C.],
- Fig. 5
- 2 shows a diagram in which the specific resistance rho [Ω · cm] of two PTC resistors (10, 11) based on a thermoplastic polymer produced by the process according to the invention is shown as a function of the temperature [° C.],
- Fig. 6
- a diagram in which the specific cold resistance [mΩ · cm] of four PTC resistance families I, II, III, IV each based on an epoxy or thermoplastic and each with the same filler fraction as a function of the mean diameter of the filler particles is shown, and
- Fig. 7
- a diagram in which the specific resistance [Ω · cm] of a PTC resistor based on a high-temperature thermoplastic is shown as a function of temperature [° C].
In Fig.1 ist ein PTC-Widerstand mit einem zwischen zwei Anschlusselektroden e₁, e₂ angeordneten Widerstandskörper w dargestellt. Dieser Widerstandskörper w ist aus einem Material mit einem vergleichsweise geringen spezifischen Kaltwiderstand von typischerweise einigen mΩ·cm und weist im Verhältnis zu seiner Querschnittsfläche von beispielsweise einigen Quadratzentimetern eine vergleichsweise grosse, im Zentimeterbereich liegende Länge auf. Sein Widerstandshub, ist grösser 10⁸ und beträgt typischerweise 10¹⁰-10¹˙. Die genannten Eigenschaften begünstigen seine Verwendung für Leistungsanwendungen im kV-Spannungsbereich, da er trotz seiner grossen Länge bei Dauerbelastung noch eine relativ hohe Stromdichte führen kann und da er nach dem PTC-Übergang im hochohmigen Zustand problemlos hohe Spannungen halten kann. Zugleich weist der Widerstandskörper w eine hohe PTC-Übergangstemperatur von typischerweise mehr als 130°C auf. Dies ermöglicht eine höhere Arbeitstemperatur des Widerstandes. Da die durch freie oder erzwungene Konvektion bedingte Kühlung des Widerstands proportional der Differenz zwischen Arbeitstemperatur und der Umgebungstemperatur ist, und da die durch Abstrahlung bedingte Kühlung sogar proportional der vierten Potenz der Arbeitstemperatur ist, kann dieser Widerstand mit vergleichsweise hohen Nennströmen belastet werden, ohne dass er unzulässig hoch erwärmt wird.In Fig.1 a PTC resistor is shown with a arranged between two connection electrodes e₁, e₂ resistor body w. This resistance body w is made of a material with a comparatively low specific cold resistance of typically a few mΩ.cm and has a comparatively large length in the centimeter range in relation to its cross-sectional area of, for example, a few square centimeters. Its resistance stroke is greater than 10⁸ and is typically 10¹⁰-10¹˙. The properties mentioned favor its use for power applications in the kV voltage range because, despite its long length, it can still carry a relatively high current density under continuous load and because it can easily withstand high voltages after the PTC transition in the high-resistance state. At the same time, the resistance body w has a high PTC transition temperature of typically more than 130 ° C. This enables a higher working temperature of the resistor. Since the cooling of the resistance caused by free or forced convection is proportional to the difference between the working temperature and the ambient temperature, and since the cooling caused by radiation is even proportional to the fourth power of the working temperature, it can Resistor can be loaded with comparatively high nominal currents without it being heated to an unacceptably high level.
Nachfolgend werden Verfahren beschrieben, welche eine besonders vorteilhafte Fertigung dieses Widerstands ermöglicht haben: In einem Mischer wurden elektrisch leitfähige, pulverförmige Füllstoffe, welche zuvor unter Vakuum oder unter einer nichtoxidierenden Atmosphäre, insbesondere unter Schutzgas, wie Stickstoff oder Argon, gelagert und/oder chemisch geätzt wurden, mit flüssigen Harzen auf der Basis von Epoxid homogen vermengt. Um bei der nachfolgenden Weiterverarbeitung Sedimentation zu vermeiden, wurde das Harz hierbei bei erhöhter Temperatur, von beispielsweise 50-80°C, angeliert. Nach Zugabe eines Härters, vorzugsweise auf der Basis von Diciandiamid oder Anhydrid, wurde das resultierende Gemisch in eine Form gegossen oder im Spritzguss verarbeitet und bei Temperaturen zwischen 120 und 220°C zu den Widerstandskörpern w ausgehärtet. Die Elektroden e₁, e₂ wurden nach dem Aushärten im allgemeinen auf polierte Stirnflächen der Widerstandskörper aufgedampft oder aufgeklebt, wurden zum Teil aber bereits schon beim Giessen und nachfolgenden Aushärten in den Widerstand eingebaut.In the following, methods are described which have made this resistor particularly advantageous to manufacture: electrically conductive, powdery fillers which were previously stored and / or chemically etched under vacuum or under a non-oxidizing atmosphere, in particular under a protective gas such as nitrogen or argon, were placed in a mixer were mixed homogeneously with liquid resins based on epoxy. In order to avoid sedimentation during the subsequent processing, the resin was gelled at an elevated temperature, for example 50-80 ° C. After adding a hardener, preferably based on diciandiamide or anhydride, the resulting mixture was poured into a mold or processed by injection molding and cured at temperatures between 120 and 220 ° C. to form the resistance bodies w. The
In weiteren Ausführungsbeispielen wurden pulverförmige, elektrisch leitfähige Füllstoffe, welche zuvor unter Vakuum oder unter einer nichtoxidierenden Atmosphäre, insbesondere Schutzgas, wie Stickstoff oder Argon, gelagert und/oder chemisch geätzt wurden, mit pulverförmigen Thermoplasten vermischt. Die resultierenden Mischungen wurden zusammen mit den Elektroden in Formen gefüllt und bei erhöhter Temperatur zu den Widerständen verpresst.In further exemplary embodiments, powdery, electrically conductive fillers which were previously stored and / or chemically etched under vacuum or under a non-oxidizing atmosphere, in particular protective gas, such as nitrogen or argon, were mixed with powdery thermoplastics. The resulting mixtures were filled into molds together with the electrodes and pressed into the resistors at elevated temperature.
Die verwendeten Ausgangsmaterialien, die Temperaturbedingungen beim Härten der Epoxide, die Temperatur- und Druckbedingungen beim Pressen der Thermoplaste und die physikalischen Eigenschaften der nach dem erfindungsgemässen Verfahren hergestellten PTC-Widerstände, wie PTC-Übergangstemperatur, Glasübergangstemperatur und spezifischer elektrischer Kaltwiderstand, sind aus den nachfolgenden beiden Tabellen sowie aus den Figuren 2 bis 5 sowie 7 zu entnehmen.
Aus den Tabellen und Fig.2 ist ersichtlich, dass durch Wahl eines geeigneten Epoxids mit einer Glasübergangstemperatur grösser 100°C und eines geeignet ausgebildeten und vorbehandelten Füllstoffs ausreichender Härte ein PTC-Widerstand (Beispiel 1) mit einem geringen spezifischen Kaltwiderstand, mit einer hohen PTC-Übergangstemperatur und mit einem Widerstandshub grösser 10⁸ hergestellt werden kann. Gegenüber einem vergleichbar bemessenen - aber nach dem Stand der Technik hergestellten - PTC-Widerstand etwa auf der Basis von Epoxy und TiB₂ (Beispiel 8) oder Polyäthlen und TiB₂ (Beispiele 15, 16) weist ein solcher Widerstand einen geringeren Kaltwiderstand und eine höhere PTC-Übergangstemperatur auf, was seinen Einsatz für Leistungsanwendungen begünstigt. Aus Fig.2 ersichtlich ist auch die Wichtigkeit der Wahl des geeigneten Füllstoffs. Ist nämlich der Füllstoff zu weich gewählt (Beispiel 2), so verkleben die Füllstoffteilchen und tritt ein PTC-Übergang nicht mehr auf.From the tables and Fig. 2 it can be seen that by choosing a suitable epoxy with a glass transition temperature greater than 100 ° C and a suitably designed and pretreated filler of sufficient hardness, a PTC resistance (Example 1) with a low specific cold resistance, with a high PTC -Transition temperature and can be produced with a resistance stroke greater than 10⁸. Compared to a comparable dimensioned - but manufactured according to the prior art - PTC resistor, for example based on epoxy and TiB₂ (example 8) or polyethylene and TiB₂ (examples 15, 16), such a resistor has a lower cold resistance and a higher PTC resistance Transition temperature, which favors its use for power applications. The importance of choosing the suitable filler can also be seen from FIG. If the filler is too soft (example 2), the filler particles stick together and a PTC transition no longer occurs.
Aus den Tabellen und den Figuren 2, 3 und 4 ist ersichtlich, dass durch geeignete Wärmebehandlung die PTC-Übergangstemperaturen der nach dem erfindungsgemässen Verfahren hergestellten PTC-Widerstände zum Teil ganz beträchtlich erhöht werden. Derart behandelte Widerstände können bei höheren Arbeitstemperaturen betrieben werden und weisen somit eine grössere Nennstromtragfähigkeit als nicht wärmebehandelte Widerstände auf. Eine geeignete Wärmebehandlung ist im allgemeinen ein mehrstündiges Härten oder Nachhärten bei einer gegenüber der üblichen Härtetemperatur (Beispiele 3, 5, 8, 14) erhöhten Temperatur (Beispiele 4, 7, 9), kann aber auch in einem mehrstündigen Nachhärten bei einer vergleichsweise tiefen Temperatur bestehen (Beispiel 6). Bei geeigneter Wahl des Epoxids lassen sich so bei geeignet ausgeführtem Aushärten PTC-Übergangstemperaturen Tc bis zu 200°C erreichen. Der spezifische Kaltwiderstand rho der wärmebehandelten Widerstände übertrifft denjenigen unbehandelter Widerstände oft erheblich. Da der spezifische Widerstand selbst bei Temperaturen bis 150°C kleiner 1 Ω·cm ist, können geeignet hergestellte Widerstände (Beispiele 4, 6, 7) zur Nennstromführung in Vorrichtungen eingesetzt werden, in denen über grosse Zeiträume Temperaturen von 100 bis 150 °C auftreten.It can be seen from the tables and FIGS. 2, 3 and 4 that the PTC transition temperatures of the PTC resistors produced by the method according to the invention can in some cases be increased considerably by suitable heat treatment. Resistors treated in this way can be operated at higher working temperatures and therefore have a higher rated current carrying capacity than resistors that have not been heat-treated. A suitable heat treatment is generally curing for several hours or post-curing at a temperature which is higher than the usual curing temperature (Examples 3, 5, 8, 14) (Examples 4, 7, 9), but can also be carried out in post-curing for several hours at a comparatively low temperature exist (Example 6). With a suitable choice of epoxy, PTC transition temperatures T c of up to 200 ° C. can be achieved with suitably designed curing. The specific cold resistance rho of the heat-treated resistors often significantly exceeds that of untreated resistors. Since the specific resistance is less than 1 Ω · cm even at temperatures up to 150 ° C, suitably manufactured resistors (examples 4, 6, 7) can be used for rated current supply in devices in which temperatures of 100 to 150 ° C occur over long periods .
Besonders hohe PTC-Übergangstemperaturen können mit bestimmten thermoplastischen Polymeren erreicht werden. Aus den Tabellen und den Figuren 5 und 7 ist ersichtlich, dass mit Polyphenylensulfid (PPS) oder syndiotaktischem Polystyrol (s-PS) als Polymer und TiB₂ als Füllstoff PTC-Übergangstemperaturen von mindestens 250°C erreicht werden. Da der spezifische Widerstand eines aus einem derartigen Material hergestellten Widerstands selbst bei Temperaturen von 190-220°C kleiner 1 Ω·cm ist, kann ein solcher Widerstand einen verhältnismässig hohen Nennstrom tragen. Durch geeignete Wärmebehandlung (Beispiel 11) wird der spezifische Widerstand zwischen 180 und 270°C zum überwiegenden Teil ganz erheblich herabgesetzt, wodurch dessen Nennstromtragfähigkeit bei den genannten hohen Temperaturen gegenüber einem nicht wärmebehandelten Widerstand ganz wesentlich heraufgesetzt wird.Particularly high PTC transition temperatures can be achieved with certain thermoplastic polymers. From the tables and Figures 5 and 7 it can be seen that with polyphenylene sulfide (PPS) or syndiotactic polystyrene (s-PS) as a polymer and TiB₂ as a filler PTC transition temperatures of at least 250 ° C can be achieved. Since the resistivity of a resistor made from such a material is less than 1 Ω · cm even at temperatures of 190-220 ° C., such a resistor can carry a relatively high nominal current. By means of suitable heat treatment (example 11), the specific resistance between 180 and 270 ° C. is for the most part very considerably reduced, as a result of which the nominal current carrying capacity at the high temperatures mentioned is significantly increased compared to a non-heat-treated resistor.
Die Stromtragfähigkeit eines erfindungsgemäss ausgebildeten PTC-Widerstands aus PPS und TiB₂ (Beispiel 10) von annähernd quaderförmiger Gestalt (Länge ca. 20 mm, Querschnitt ca. 30 mm) wurde mit einem PTC-Widerstand nach dem Stand der Technik aus PE und TiB₂ (Beispiel 15) mit entsprechenden Abmessungen verglichen. Hierbei waren die PTC-Widerstände in einem Wasserbad (T=65°C) mit direkter Anströmung (20 l/min) der PTC-Widerstände mit Wasser von ebenfalls 65°C angeordnet. Durch die Widerstände wurde während ca. 6 min ein konstanter Strom geführt. Trat während dieser Zeit kein PTC-Übergang auf, wurde der Strom vergrössert und der Messzyklus wiederholt. Als Mass für die Stromtragfähigkeit wurde der Stromwert ermittelt, bei dem gerade noch kein PTC-Übergang auftrat. Für den Widerstand nach der Erfindung ergab sich so eine Stromdichte von ca. 120 A/cm, für den Widerstand nach dem Stand der Technik hingegen nur eine Stromdichte von ca. 50 A/cm.The current carrying capacity of a PTC resistor made according to the invention made of PPS and TiB₂ (example 10) of approximately cuboid shape (length approx. 20 mm, cross section approx. 30 mm) was made with a prior art PTC resistor made of PE and TiB₂ (example 15) compared with corresponding dimensions. Here, the PTC resistors were arranged in a water bath (T = 65 ° C) with a direct flow (20 l / min) of the PTC resistors with water likewise at 65 ° C. A constant current was passed through the resistors for about 6 minutes. If there was no PTC transition during this time, the current was increased and the measuring cycle repeated. As a measure of the current carrying capacity, the current value was determined at which there was just no PTC transition. This resulted in a current density of approximately 120 A / cm for the resistor according to the invention, but only a current density of approximately 50 A / cm for the resistor according to the prior art.
Aus den Tabellen ist ersichtlich, dass bei einem PTC-Widerstand gemäss den Beispielen 12a-12e ein Gehalt an Füllstoff von mehr als 30 Volumenprozent vorgesehen sein sollte, um einen geringen spezifischen Kaltwiderstand zu erzielen. Entsprechendes gilt auch für alle nach dem erfindungsgemässen Verfahren hergestellten PTC-Widerstände.It can be seen from the tables that a filler content of more than 30 percent by volume should be provided for a PTC resistor according to Examples 12a-12e in order to achieve a low specific cold resistance. The same also applies to all PTC resistors produced by the method according to the invention.
Die mittleren Durchmesser der Teilchen des Füllstoffs sollten zweckmässigerweise grösser 10 µm sein, da so einerseits eine gute elektrische Kaltleitfähigkeit erreicht wird. Dies ist aus Fig.6 ersichtlich, in der der spezifische elektrische Kaltwiderstand rho (bei ca. 30°C) von vier PTC-Widerständen I (Basis Polyäthylen und 50 Vol% TiB₂), II (Basis Polyäthylen und 35 Vol% TiB₂), III (Basis Epoxid SpurrR und 35 Vol% TiB₂) und IV (Basis Polyäthylen und 60 Vol% TiB₂ gemäss Beispiel 18) in Abhängigkeit von der Grösse ps der Füllstoffteilchen dargestellt ist. Sind die Teilchen grösser 60 µm bzw. 100 µm, so wird eine besonders gute elektrische Kaltleitfähigkeit erreicht. Um eine gute Verarbeitbarkeit der Ausgangskomponenten bei der Herstellung der erfindungsgemässen Widerstände zu gewährleisten, ist es zweckmässig, die Grösse der Füllstoffteilchen auf 500 µm, vorzugsweise sogar auf 200 µm zu begrenzen. Die Füllstoffteilchen können in Form von Fraktionen vorliegen mit typischen mittleren Teilchendurchmessern zwischen 100 µm und 200 µm oder 63 µm und 100 µm oder gegebenenfalls auch zwischen 32 µm und 45 µm oder aber 10 und 32 µm. Ein relativ kleiner spezifischer Kaltwiderstand wird auch dann erreicht, wenn der Füllstoff einen relativ grossen Volumenanteil an groben Teilchen mit mittleren Durchmessern von beispielsweise 63 µm bis 100 µm und einen relativ kleinen-Volumenanteil an feinen Teilchen mit Durchmessern bis beispielsweise 10 µm aufweist.The average diameter of the particles of the filler should expediently be greater than 10 μm, since on the one hand good electrical cold conductivity is achieved. This can be seen from Fig. 6, in which the specific electrical cold resistance rho (at approx. 30 ° C) of four PTC resistors I (based on polyethylene and 50 vol% TiB₂), II (based on polyethylene and 35 vol% TiB₂), III (based on epoxy Spurr R and 35% by volume TiB₂) and IV (based on polyethylene and 60% by volume TiB₂ according to Example 18) depending on the size ps of the filler particles. If the particles are larger than 60 µm or 100 µm, particularly good electrical cold conductivity is achieved. To ensure good processability of the starting components in the manufacture of the resistors according to the invention ensure, it is appropriate to limit the size of the filler particles to 500 microns, preferably even to 200 microns. The filler particles can be present in the form of fractions with typical mean particle diameters between 100 μm and 200 μm or 63 μm and 100 μm or optionally also between 32 μm and 45 μm or 10 and 32 μm. A relatively small specific cold resistance is also achieved if the filler has a relatively large volume fraction of coarse particles with average diameters of, for example, 63 μm to 100 μm and a relatively small volume fraction of fine particles with diameters of up to 10 μm, for example.
Claims (14)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19944427161 DE4427161A1 (en) | 1994-08-01 | 1994-08-01 | Process for the manufacture of a PTC resistor and resistor produced thereafter |
| DE4427161 | 1994-08-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| EP0696036A1 true EP0696036A1 (en) | 1996-02-07 |
Family
ID=6524622
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP95810464A Withdrawn EP0696036A1 (en) | 1994-08-01 | 1995-07-12 | Process for the preparation of a PTC resistance and resistance obtained therefrom |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0696036A1 (en) |
| JP (1) | JPH08191003A (en) |
| DE (1) | DE4427161A1 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0866473A1 (en) * | 1997-03-13 | 1998-09-23 | Ngk Insulators, Ltd. | Composite PTC material |
| EP0866471A1 (en) * | 1997-02-28 | 1998-09-23 | Mitsubishi Denki Kabushiki Kaisha | Polymeric PTC composition and circuit protection device made from the same |
| EP0923086A1 (en) * | 1997-12-11 | 1999-06-16 | Abb Research Ltd. | Protection element |
| EP0932166A1 (en) * | 1998-01-22 | 1999-07-28 | Mitsubishi Denki Kabushiki Kaisha | Polymeric PTC composition and circuit protection device made therefrom |
| WO2002079302A1 (en) * | 2001-03-28 | 2002-10-10 | Perplas Ltd | Composite obtainable by sintering an inorganic material with one or more polymers |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19800470A1 (en) * | 1998-01-09 | 1999-07-15 | Abb Research Ltd | Resistor element for current limiting purposes especially during short-circuits |
| DE19824104B4 (en) * | 1998-04-27 | 2009-12-24 | Abb Research Ltd. | Non-linear resistor with varistor behavior |
| DE19839631C1 (en) * | 1998-08-31 | 2000-03-30 | Siemens Matsushita Components | Production of a temperature sensor, especially a thermistor, comprises liberating the sensor element from residual moisture before encapsulating in a vacuum and dipping into a polymeric solution to form a polymer layer |
| DE10225938C1 (en) * | 2002-06-11 | 2003-12-18 | Webasto Thermosysteme Gmbh | Over-heating detector uses temperature sensor in the form of polymer element with fibres or bands extending across monitored surface |
| US20100015522A1 (en) * | 2005-05-16 | 2010-01-21 | Takashi Hasunuma | Sealing piece and battery pack using the same |
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| WO1993026014A1 (en) * | 1992-06-05 | 1993-12-23 | Raychem Corporation | Conductive polymer composition |
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| US3243753A (en) * | 1962-11-13 | 1966-03-29 | Kohler Fred | Resistance element |
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| DE3447391A1 (en) * | 1984-12-27 | 1986-07-03 | Otsuka Kagaku K.K., Osaka | ELECTRICALLY CONDUCTIVE ALKALINE METAL TITANATE COMPOSITION AND MOLDED PARTS THEREOF |
| JPH0777161B2 (en) * | 1986-10-24 | 1995-08-16 | 日本メクトロン株式会社 | PTC composition, method for producing the same and PTC element |
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| JPH0286087A (en) * | 1988-09-21 | 1990-03-27 | Tdk Corp | Polymer ptc element |
| WO1991019297A1 (en) | 1990-06-05 | 1991-12-12 | Asea Brown Boveri Ab | Method of manufacturing an electrical device |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0866471A1 (en) * | 1997-02-28 | 1998-09-23 | Mitsubishi Denki Kabushiki Kaisha | Polymeric PTC composition and circuit protection device made from the same |
| EP0866473A1 (en) * | 1997-03-13 | 1998-09-23 | Ngk Insulators, Ltd. | Composite PTC material |
| EP0923086A1 (en) * | 1997-12-11 | 1999-06-16 | Abb Research Ltd. | Protection element |
| EP0932166A1 (en) * | 1998-01-22 | 1999-07-28 | Mitsubishi Denki Kabushiki Kaisha | Polymeric PTC composition and circuit protection device made therefrom |
| WO2002079302A1 (en) * | 2001-03-28 | 2002-10-10 | Perplas Ltd | Composite obtainable by sintering an inorganic material with one or more polymers |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH08191003A (en) | 1996-07-23 |
| DE4427161A1 (en) | 1996-02-08 |
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