EP0992042A1 - Non-linear resistance with varistor behaviour and method for the production thereof - Google Patents

Non-linear resistance with varistor behaviour and method for the production thereof

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Publication number
EP0992042A1
EP0992042A1 EP99915429A EP99915429A EP0992042A1 EP 0992042 A1 EP0992042 A1 EP 0992042A1 EP 99915429 A EP99915429 A EP 99915429A EP 99915429 A EP99915429 A EP 99915429A EP 0992042 A1 EP0992042 A1 EP 0992042A1
Authority
EP
European Patent Office
Prior art keywords
particles
varistor
electrically conductive
fraction
filler
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.)
Granted
Application number
EP99915429A
Other languages
German (de)
French (fr)
Other versions
EP0992042B1 (en
Inventor
Petra Kluge-Weiss
Felix Greuter
Ralf Struempler
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
Original Assignee
ABB Research Ltd Switzerland
ABB Research Ltd Sweden
Priority date (The priority date 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 date listed.)
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Publication date
Application filed by ABB Research Ltd Switzerland, ABB Research Ltd Sweden filed Critical ABB Research Ltd Switzerland
Publication of EP0992042A1 publication Critical patent/EP0992042A1/en
Application granted granted Critical
Publication of EP0992042B1 publication Critical patent/EP0992042B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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
    • H01C7/10—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 voltage responsive, i.e. varistors
    • H01C7/12—Overvoltage protection resistors
    • 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
    • H01C7/10—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 voltage responsive, i.e. varistors
    • H01C7/105—Varistor cores
    • H01C7/108—Metal oxide
    • H01C7/112—ZnO type

Definitions

  • the invention is based on a nonlinear resistor with varistor behavior according to the preamble of claim 1.
  • This resistor contains a matrix and a powdery filler embedded in the matrix.
  • the filler contains a sintered varistor granulate with predominantly spherical particles made of doped metal oxide.
  • the particles are made up of crystalline grains separated by grain boundaries. Since complex sintering processes turn out to be much simpler than comparable-acting resistors based on a sintered ceramic, such composite resistors can be produced relatively easily and in a wide variety of shapes.
  • the invention also relates to a method for producing this resistor.
  • This resistor consists of a polymer filled with a powder.
  • the powder used is a granulate which was produced by sintering a spray-dried varistor powder based on a zinc oxide doped with oxides of Bi, Sb, Mn, Co, Al and / or other metals. These granules have spherical particles shaped like a soccer ball with varistor behavior, which are made up of crystalline grains separated by grain boundaries.
  • the diameter of these particles are up to 300 ⁇ m.
  • the electrical properties of the sintered granulate such as the non-linearity coefficient ⁇ B or the breakdown field strength U B [V / mm] can be set over a wide range.
  • a resistance has a higher non-linearity coefficient and a higher breakthrough field strength when the proportion of filler decreases.
  • WO 97/26693 describes a composite material based on a polymeric matrix and a powder embedded in this matrix.
  • a granulate is used as the powder, which was also produced by sintering a spray-dried varistor powder based on a zinc oxide doped with oxides of Bi, Sb, Mn, Co, Al and / or other metals.
  • These granules have spherical particles shaped like a soccer ball with varistor behavior, which are made up of crystalline grains separated by grain boundaries. The particles have a diameter of up to 125 ⁇ m and have a size distribution that follows a Gaussian distribution.
  • This material is used in cable connections and cable terminations and forms voltage-control layers there.
  • US 4,726,991, US 4,992,333, 5,068,634 and US 5,294,374 specify voltage-limiting resistors made of a polymer and a powdery filler material based on conductive and / or semiconducting particles. With these resistors, overvoltage protection is achieved by dielectric breakdown of the polymer. Since relatively high temperatures can occur here, the overvoltage protection should not be reversible and the energy absorption capacity should be relatively low.
  • the invention is based on the object of specifying a resistor of the type mentioned at the outset, which is distinguished by a high power consumption despite a large non-linearity coefficient for good protection characteristics, and at the same time a method create with which such a resistor can be produced in a particularly advantageous manner.
  • a suitable filler electrical properties are achieved in the resistor according to the invention that come relatively close to a varistor based on a ceramic. It is essential here that either a suitably structured conductive additional filler is provided and / or that a varistor granulate is used which enables a particularly high packing density. It is then possible to use a technology known from injection molding, extrusion or casting resin technology to produce resistors with varistor behavior in a comparatively simple manner, which are characterized by good protection characteristics and high power consumption. It is particularly advantageous here that, by suitable choice of the output components and by means of process parameters which are easy to set, varistors can be produced which, with regard to their shape and their physical properties, have a broad spectrum and in particular a relatively high energy absorption or switching capacity.
  • the non-linear resistor according to the invention can advantageously be used as a field-controlling element in cable fittings or as an overvoltage protection element (varistor). It can be used in both low and medium and high voltage technology and, due to its ease of manufacture and further processing, can easily have a complex geometry. If necessary, it can be molded on, for example as a protective and / or control element, by casting directly onto an electrical apparatus, for example a circuit breaker, or applied as a thin lacquer coating. It can also be used in hybrid printing for integrated circuits.
  • the electrically conductive particles provided in addition to the varistor particles in the filler are connected to the varistor particles on their surfaces before the filler and the matrix material are brought together.
  • the electrically conductive particles cannot be detached from the surfaces of the varistor particles with great certainty, so that resistors produced by this method Excellent electrical properties, especially extremely stable current-voltage characteristics.
  • the method according to the invention ensures that the electrically conductive particles are distributed uniformly over the surfaces of the varistor particles and form an atomic bond with the varistor material.
  • the contact effect of the filler is thus significantly improved and it is sufficient to have a relatively small proportion of electrically conductive particles in the filler in order to obtain resistors with excellent electrical properties, such as, in particular, a large current carrying capacity.
  • Nonlinear resistors with varistor behavior designed as varistor composites were produced by mixing polymeric material with a filler. Such mixing processes are well known from the prior art and need not be explained in more detail.
  • the polymers can be thermosets, such as, in particular, epoxy or polyester resins, polyurethanes or silicones, or thermoplastics, for example HDPE, PEEK or ETFE.
  • a gel e.g. silicone gel
  • a liquid e.g. silicone oil, polybutane, ester oil, fats
  • a gas air, nitrogen, SF 6 , ...), a gas mixture and / or a glass
  • a gas mixture and / or a glass can also be used.
  • the filler used here contained varistor particles made of doped metal oxide with a predominantly spherical structure, the particles being composed of crystalline grains separated from one another by grain boundaries.
  • the filler was made as follows:
  • a varistor mixture of commercially available ZnO, doped with oxides of Bi, Sb, Mn and Co as well as with Ni, Al, Si and / or one or more other metals was present as an aqueous suspension or solution processed approximately spherical granules.
  • the granules were sintered in a chamber furnace, for example on an Al 2 O 3 plate coated with ZnO, a Pt film or a ZnO ceramic, or optionally also in a rotary tube furnace.
  • the heating times during sintering were up to 300 h, typically for example 50 ° C / h or 80 ° C / h.
  • the sintering temperature was between 900 ° C and 1320 ° C.
  • the holding times during sintering were between 3 hours and 72 hours. After sintering, cooling was carried out at a rate between 50 ° C / h and 300 ° C / h.
  • the varistor granules produced in this way were subsequently separated in a vibrating device or by light mechanical rubbing. By sieving, granulate fractions with particle sizes between 90 and 160 ⁇ m, 32 and 63 ⁇ m and less than 32 ⁇ m were then produced from the separated granulate.
  • Varistor granules of the different fractions were mixed together in certain weight ratios. Some of these mixtures and some of the fractions were mixed with a metal powder with geometrically anisotropic, in particular scale-shaped, electrically conductive particles with a thickness to aspect ratio of typically 1/5 to 1/100, e.g. B. Ni-flakes, whose length was less than 60 microns on average. In any case, the length of the metal particles was chosen so that on average it was smaller than the radius of an average sized particle of the coarse (90 - 160 ⁇ m) varistor granules. This and a small proportion, typically 0.05 to 5 percent by volume, of the varistor granulate prevented the formation of metallically conductive percolation paths in the mixture.
  • the starting components of the filler were generally premixed in a turbo mixer for several hours. If one of the starting components was the metal powder, its particles lay against the surfaces of the spherical varistor particles, so that particularly low-resistance contacts were created between the individual varistor particles. In addition, smaller particles fall inside the varistor particles, which are designed as a hollow sphere to a small percentage, and thus help to reduce current supply bottlenecks.
  • Fine platelets, easily deformable, soft particles and / or short fibers are also conceivable as metallic fillers.
  • a metallic filler with particles that melt in the area of the highest processing temperatures, preferentially accumulate in the contact points of the varistor particles and lead there to an improved local contact is advantageous.
  • fine powders for example based on silver, copper, aluminum, gold, indium and their alloys, or conductive oxides, borides, carbides with particle diameters preferably between 1 and 20 ⁇ m can also be used as the metallic filler.
  • the particles of these powders can easily be spherical.
  • the electrically conductive particles contained in the filler should be connected to the varistor particles on their surfaces.
  • the content of conductive electrical particles can then be low and have a lower value of 0.05 percent by volume.
  • Such a surface connection can advantageously be achieved by heat treatment.
  • the varistor particles and the electrically conductive particles have been mixed, these particles initially adhere well to the surfaces of the varistor particles.
  • the matrix material for example a polymer, a gel or an oil, for example based on a silicone
  • some of the electrically conductive particles float on the matrix material and then significantly impair the dielectric strength of such a resistance produced in this way .
  • processes initiated by the heat treatment in particular diffusion processes, firmly bond the electrically conductive particles to the surface.
  • floating of the electrically conductive particles on the matrix material is avoided.
  • Loose particles which may be present in the heat-treated filler can preferably be removed by washing, sieving or air sifting before being combined with the matrix material.
  • the temperatures required for the heat treatment are essentially determined by the material of the electrically conductive particles. For silver with a treatment time of approx. 3 h, a heat treatment temperature of approx. 400 ° C has proven to be sufficient. Higher temperatures (up to 900 ° C) are possible, however care must be taken to ensure that the electrical properties of the varistor particles do not change too much. Such changes could occur, for example, through a reaction of the material of the electrically conductive particles with the bismuth phase of the varistor particles.
  • Good surface connections are also obtained in that powder containing varistor particles is dispersed in a metal-containing solution or dispersion, and in that the surface connection is produced by wet-chemical precipitation of the disperse solution or dispersion or by electrochemical or galvanic deposition. This connection can be strengthened by subsequent heat treatment.
  • Solid surface connections between the varistor particles and the electrically conductive particles can also be produced by dispersing a powder containing varistor particles in a metal-containing solution or dispersion, and by subsequent reactive spray drying or spray pyrolysis of the disperse solution or dispersion. Surface coating from the gas phase is also possible, as is advantageously achieved by sputtering, vapor deposition or spraying, for example in a fluidized bed or in a powder stream containing varistor granules and gas.
  • an advantageous surface coating is also achieved by friction contacting.
  • the varistor granules or at least a part thereof and / or the electrically conductive particles in a mixer are added with friction material made of the material to the electrically conductive particles and / or the lining of the mixer contains material of the electrically conductive particles.
  • the surface coating can also be achieved by introducing the varistor granules and the electrically conductive particles into a mechano-fusion system, as is sold, for example, by Hosokawa Micron Europe B.V., 2003 RT Haarlem, Holland.
  • the matrix contains a silicone
  • the adhesive strength of the filler in the matrix is then optimized.
  • adhesion promoters are generally applied to the filler in the form of a thin layer. Suitable adhesion promoters are, for example, silanes, titanates, zirconates, aluminates and / or chelates.
  • the electrically conductive particles can also be added to the adhesion promoter and can therefore be used in an economically particularly advantageous manner in the same application process.
  • Resistor bodies were manufactured, from which test resistors with a volume of a few mm 3 to a few dm 3 were realized by sawing, grinding and attaching two electrodes, for example by coating with a metal such as gold or aluminum. Test specimens were also produced in which the electrodes were cast directly with a casting resin, such as an epoxy or a silicone. The following table shows the compositions of four of these test resistors, where D means the diameter of the particles of the varistor granules.
  • Resistor 1 was state of the art.
  • resistor 3 had a proportion of 5% by volume of the filler in electrically conductive Ni-flakes.
  • the resistor 4 had both a portion of the fine-grained varistor granules amounting to approx. 10% by volume of the filler and an amount of electrically conductive Ni-flakes amounting to approx. 3% by volume.
  • the breakdown field strength U B [V / mm], the nonlinearity coefficient ⁇ B and the maximum power P [J / cm 3 ] were determined on this / ier resistors, as can be seen from the table below.
  • U B and ⁇ a variable DC voltage was applied to the resistors and the resistors were exposed to electrical field strengths between approx. 5 and approx. 500 [V / mm].
  • the current density J [A / cm 2 ] flowing in each of the resistors was determined.
  • the values of U and J determined in this way determined the current-voltage characteristics of the resistors.
  • the breakdown field strength U B of the associated resistor was determined from each of the characteristic curves at a current density of 1.3 ⁇ 3 "4 [A / cm 2 ]. ⁇ 8 was doubled for each of the resistors from the slope of the tangent to the assigned current-voltage characteristic curve taken logarithmically at the point determined by the breakthrough field strength U B.
  • the resistors 2 to 4 with respect to the resistor according to the prior art (resistance 1) ⁇ both by a larger non-linearity coefficient B and are characterized by an increased power consumption P and the lower at the same time the breakdown field strength.
  • this is a result of the improved contacting of the individual varistor particles with one another due to the electrically conductive particles additionally contained in the mixture, and on the other hand, it is a result of a particularly high density of varistor particles.
  • This high density is created by a varistor granulate with two fractions of particles of different sizes, of which the particles of the first fraction have a larger diameter than the particles of the second fraction and are arranged essentially in the form of a dense spherical packing and the particles of the second fraction Fill in the gaps formed by the ball packing.
  • the diameter of the particles of the first fraction are preferably between approximately 40 and approximately 200 ⁇ m. In order to achieve a high density, it is particularly favorable if the diameter of the particles of the second fraction is approximately 10 to approximately 50% of the diameter of the particles of the first fraction, and if the proportion of the second fraction is approximately 5 to approximately 30% by volume the proportion of the first fraction.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Thermistors And Varistors (AREA)
  • Adjustable Resistors (AREA)
  • Control Of Electric Motors In General (AREA)
  • Making Paper Articles (AREA)

Abstract

The nonlinear resistor has varistor behaviour and has a matrix and a filler in powder form which is embedded in the matrix. The filler contains sintered varistor granules with predominantly spherical particles of doped metal oxide. These particles are made up of crystalline grains separated from one another by grain boundaries. The filler also contains electrically conductive particles, which cover at most a part of the surfaces of the spherical particles, and/or the varistor granules contain two fractions of particles with different sizes, of which the particles in the first fraction have larger diameters than the particles in the second fraction and are arranged essentially in the form of close sphere packing and the particles in the second fraction fill the interstices formed by the sphere packing.The resistor can be produced straightforwardly and cost-effectively and is distinguished by a high nonlinearity coefficient, which is desired for a good protection characteristic, and by a high power acceptance.

Description

B E S C H R E I B U N G DESCRIPTION
Nichtlinearer Widerstand mit Varistorverhalten und Verfahren zur Herstellung dieses WiderstandsNonlinear resistor with varistor behavior and method for producing this resistor
TECHNISCHES GEBIETTECHNICAL AREA
Bei der Erfindung wird ausgegangen von einem nichtlinearen Widerstand mit Varistorverhalten nach dem Oberbegriff von Patentanspruch 1. Dieser Widerstand enthält eine Matrix und einen in die Matrix eingebetteten, pulverförmigen Füllstoff. Der Füllstoff enthält ein gesintertes Varistorgranulat mit überwiegend kugelförmigenTeilchen aus dotiertem Metalloxid. Die Teilchen sind aus kristallinen, durch Korngrenzen voneinander getrennten Körner aufgebaut. Da gegenüber vergleichbar wirkenden Widerständen auf der Basis einer Sinterkeramik aufwendige Sinterprozesse wesentlich einfacher ausfallen, können derartige Kompositwiderstände relativ einfach und in grosser Formenvielfalt hergestellt werden. Die Erfindung betrifft zugleich auch ein Verfahren zur Herstellung dieses Widerstands.The invention is based on a nonlinear resistor with varistor behavior according to the preamble of claim 1. This resistor contains a matrix and a powdery filler embedded in the matrix. The filler contains a sintered varistor granulate with predominantly spherical particles made of doped metal oxide. The particles are made up of crystalline grains separated by grain boundaries. Since complex sintering processes turn out to be much simpler than comparable-acting resistors based on a sintered ceramic, such composite resistors can be produced relatively easily and in a wide variety of shapes. The invention also relates to a method for producing this resistor.
STAND DER TECHNIKSTATE OF THE ART
Ein Widerstand der vorgenannten Art ist in R.Strümpler, P.Kluge-Weiss und F.Greuter "Smart Varistor Composites", Proceedings of the 8th CIMTECH-World Ceramic Coπgress and Forum on New Materials, Symposium VI (Florence, June 29 - Jury 4, 1994) beschrieben. Dieser Widerstand besteht aus einem mit einem Pulver gefüllten Polymer. Als Pulver wird ein Granulat verwendet, welches durch Sintern eiηes sprühgetrockneten Varistorpulvers auf der Basis eines mit Oxiden von Bi, Sb, Mn, Co, AI und/oder weiterer Metallen dotierten Zinkoxids erzeugt wurde. Dieses Granulat weist nach Art eines Fussballs geformte, kugelförmige Teilchen mit Varistorverhalten auf, welche aus kristallinen, durch Korngrenzen voneinander getrennten Körnern aufgebaut sind. Die Durchmesser dieser Teilchen betragen bis zu 300 μm. Durch Veränderung der Dotierstoffe und der Sinterbedingungen können die elektrischen Eigenschaften des Sintergranulats, wie der Nichtlinearitätskoeffizient αB oder die Durchbruchfeldstärke UB [V/mm] über einen grossen Bereich eingestellt werden. Bei gleichen Ausgangsstoffen weist ein solcher Widerstand einen höheren Nichtlinearitätskoeffizienten und eine höhere Durchbruchfeldstärke auf, wenn der Füllstoffanteil abnimmt. Es hat sich aber gezeigt, dass dann beim Begrenzen einer Spannung das Aufnahmevermögen für Energie relativ gering ist.A resistance of the aforementioned kind is described in R. Strümpler, P. Kluge-Weiss and F. Greuter "Smart Varistor Composites", Proceedings of the 8th CIMTECH-World Ceramic Congress and Forum on New Materials, Symposium VI (Florence, June 29 - Jury 4, 1994). This resistor consists of a polymer filled with a powder. The powder used is a granulate which was produced by sintering a spray-dried varistor powder based on a zinc oxide doped with oxides of Bi, Sb, Mn, Co, Al and / or other metals. These granules have spherical particles shaped like a soccer ball with varistor behavior, which are made up of crystalline grains separated by grain boundaries. The diameter of these particles are up to 300 μm. By changing the dopants and the sintering conditions, the electrical properties of the sintered granulate, such as the non-linearity coefficient α B or the breakdown field strength U B [V / mm], can be set over a wide range. With the same starting materials, such a resistance has a higher non-linearity coefficient and a higher breakthrough field strength when the proportion of filler decreases. However, it has been shown that when a voltage is limited, the absorption capacity for energy is relatively low.
In WO 97/26693 ist ein Verbundmaterial auf der Basis einer polymeren Matrix und eines in diese Matrix eingebetteten Pulvers beschrieben. Als Pulver wird ein Granulat verwendet, welches ebenfalls durch Sintern eines sprühgetrockneten Varistorpulvers auf der Basis eines mit Oxiden von Bi, Sb, Mn, Co, AI und/oder weiterer Metalle dotierten Zinkoxids erzeugt wurde. Dieses Granulat weist nach Art eines Fussballs geformte, kugelförmige Teilchen mit Varistorverhalten auf, welche aus kristallinen, durch Korngrenzen voneinander getrennten Körnern aufgebaut sind. Die Teilchen haben Durchmesser bis höchstens 125 μm und weisen eine Grössenverteilung auf, welche einer Gaussverteilung folgt. Dieses Material wird in Kabelverbindungen und Kabelendverschlüssen eingesetzt und bildet dort spannungssteuemde Schichten.WO 97/26693 describes a composite material based on a polymeric matrix and a powder embedded in this matrix. A granulate is used as the powder, which was also produced by sintering a spray-dried varistor powder based on a zinc oxide doped with oxides of Bi, Sb, Mn, Co, Al and / or other metals. These granules have spherical particles shaped like a soccer ball with varistor behavior, which are made up of crystalline grains separated by grain boundaries. The particles have a diameter of up to 125 μm and have a size distribution that follows a Gaussian distribution. This material is used in cable connections and cable terminations and forms voltage-control layers there.
In US 4,726,991 , US 4,992,333, 5,068,634 und US 5,294,374 sind spannungsbegrenzende Widerstände aus einem Polymer und einem pulverförmigen Füllmaterial auf der Basis von leitenden und/oder halbleitenden Teilchen angegeben. Bei diesen Widerständen wird der Überpannungsschutz durch dielektrischen Durchbruch des Polymers erreicht. Da hierbei relativ hohe Temperaturen auftreten können, dürften der Überspannungsschutz nicht reversibel und das Energieaufnahmevermögen relativ gering sein.US 4,726,991, US 4,992,333, 5,068,634 and US 5,294,374 specify voltage-limiting resistors made of a polymer and a powdery filler material based on conductive and / or semiconducting particles. With these resistors, overvoltage protection is achieved by dielectric breakdown of the polymer. Since relatively high temperatures can occur here, the overvoltage protection should not be reversible and the energy absorption capacity should be relatively low.
KURZE DARSTELLUNG DER ERFINDUNGSUMMARY OF THE INVENTION
Der Erfindung, wie sie in den Patentansprüchen angegeben ist, liegt die Aufgabe zugrunde, einen Widerstand der eingangs genannten Art anzugeben, welcher sich trotz eines für eine gute Schutzcharakteristik grossen Nichtlinearitätskoeffizienten durch eine hohe Leistungsaufnahme auszeichnet, und zugleich ein Verfahren zu schaffen, mit dem ein solcher Widerstand in besonders vorteilhafter Weise hergestellt werden kann.The invention, as specified in the claims, is based on the object of specifying a resistor of the type mentioned at the outset, which is distinguished by a high power consumption despite a large non-linearity coefficient for good protection characteristics, and at the same time a method create with which such a resistor can be produced in a particularly advantageous manner.
Durch Auswahl eines geeigneten Füllstoffs werden beim Widerstand nach der Erfindung elektrische Eigenschaften erreicht, die einem Varistor auf der Basis einer Keramik relativ nahe kommen. Hierbei ist es wesentlich, dass entweder ein geeignet strukturierter leitfähiger Zusatzfüllstoff vorgesehen ist und/oder dass ein Varistorgranulat verwendet wird, welches eine besonders hohe Packungsdichte ermöglicht. Es können dann mit einer aus der Spritzguss-, der Extrusions- oder Giessharztechnik bekannten Technologie in vergleichsweise einfacher Weise Widerstände mir Varistorverhalten hergestellt werden, welche sich durch eine gute Schutzcharakteristik und eine hohe Leistungsaufnahme auszeichnen. Von besonderem Vorteil ist es hierbei, dass durch geeignete Wahl der Ausgangskomponenten und durch einfach einzustellende Verfahrensparameter Varistoren hergestellt werden können, welche hinsichtlich ihrer Formgebung und ihrer physikalischer Eigenschaften ein breit gefächertes Spektrum und insbesondere ein relativ hohes Energieaufnahme- bzw. Schaltvermögen aufweisen.By selecting a suitable filler, electrical properties are achieved in the resistor according to the invention that come relatively close to a varistor based on a ceramic. It is essential here that either a suitably structured conductive additional filler is provided and / or that a varistor granulate is used which enables a particularly high packing density. It is then possible to use a technology known from injection molding, extrusion or casting resin technology to produce resistors with varistor behavior in a comparatively simple manner, which are characterized by good protection characteristics and high power consumption. It is particularly advantageous here that, by suitable choice of the output components and by means of process parameters which are easy to set, varistors can be produced which, with regard to their shape and their physical properties, have a broad spectrum and in particular a relatively high energy absorption or switching capacity.
Der nichtlineare Widerstand nach der Erfindung kann mit Vorteil als feldsteuerndes Element in Kabelgarnituren oder als Überspannungsschutzelement (Varistor) verwendet werden. Er kann sowohl in der Nieder- als auch in der Mittel- und Hochspannungstechnik eingesetzt werden und kann wegen seiner einfachen Herstell- und Weiterverarbeitbarkeit ohne weiteres eine komplexe Geometrie aufweisen. Gegebenenfalls kann er, beispielsweise als Schutz- und/oder Steuerelement, durch Vergiessen direkt an einen elektrischen Apparat, beispielsweise einen Leistungsschalter, angeformt werden oder als dünne Lackbeschichtung aufgetragen werden. Weiterhin kann er im Siebdruck im Hybridverfahren für integrierte Schaltungen verwendet werden.The non-linear resistor according to the invention can advantageously be used as a field-controlling element in cable fittings or as an overvoltage protection element (varistor). It can be used in both low and medium and high voltage technology and, due to its ease of manufacture and further processing, can easily have a complex geometry. If necessary, it can be molded on, for example as a protective and / or control element, by casting directly onto an electrical apparatus, for example a circuit breaker, or applied as a thin lacquer coating. It can also be used in hybrid printing for integrated circuits.
Beim erfindungsgemässen Verfahren werden die neben den Varistorpartikeln zusätzlich im Füllstoff vorgesehenen elektrisch leitfähigen Teilchen vor dem Zusammenführen von Füllstoff und Matrixwerkstoff mit den Varistorpartikeln an deren Oberflächen verbunden. Beim Zusammenführen können sich die elektrisch leitfähigen Teilchen mit grosser Sicherheit nicht von den Oberflächen der Varistorpartikel lösen, so dass nach diesem Verfahren hergestellte Widerstände hervorragende elektrische Eigenschaften, insbesondere äusserst stabile Strom- Spannungs-Kennlinien, aufweisen.In the method according to the invention, the electrically conductive particles provided in addition to the varistor particles in the filler are connected to the varistor particles on their surfaces before the filler and the matrix material are brought together. When merging, the electrically conductive particles cannot be detached from the surfaces of the varistor particles with great certainty, so that resistors produced by this method Excellent electrical properties, especially extremely stable current-voltage characteristics.
Besonders gute elektrische. Eigenschaften werden dann erreicht, wenn noch vorhandene, lose elektrisch leitfähige Teilchen vor dem vor allem durch Mischen und Infiltrieren bewirkten Zusammenführen mit dem Matrixwerkstoff, etwa durch Waschen, Sieben oder Windsichten, aus dem Füllstoff entfernt werden.Particularly good electrical. Properties are achieved when loose, electrically conductive particles that are still present are removed from the filler before they are brought together with the matrix material, primarily by mixing and infiltration, for example by washing, sieving or air classifying.
Zugleich wird durch das erfindungsgemässe Verfahren erreicht, dass die elektrisch leitfähigen Teilchen gleichmässig über die Oberflächen der Varistorpartikel verteilt sind und mit dem Varistormaterial eine atomare Bindung eingehen. Die Kontaktwirkung des Füllstoffs wird so ganz wesentlich verbessert und es genügt ein verhältnismässig kleiner Anteil an elektrisch leitfähigen Teilchen im Füllstoff, um Widerstände mit hervorragenden elektrischen Eigenschaften, wie insbesondere einer grossen Stromtragfähigkeit, zu bekommen.At the same time, the method according to the invention ensures that the electrically conductive particles are distributed uniformly over the surfaces of the varistor particles and form an atomic bond with the varistor material. The contact effect of the filler is thus significantly improved and it is sufficient to have a relatively small proportion of electrically conductive particles in the filler in order to obtain resistors with excellent electrical properties, such as, in particular, a large current carrying capacity.
WEG ZUR AUSFÜHRUNG DER ERFINDUNGWAY OF CARRYING OUT THE INVENTION
Es wurden als Varistorkomposite ausgebildete nichtlineare Widerstände mit Varistorverhalten durch Mischen von polymerem Werkstoff mit einem Füllstoff hergestellt. Solche Mischverfahren sind aus dem Stand der Technik wohlbekannt und brauchen nicht näher erläutert zu werden. Die Polymere können Duromere, wie insbesondere Epoxid- oder Polyesterharze, Polyurethane oder Silikone oder aber Thermoplaste, beispielsweise HDPE, PEEK oder ETFE, sein. Anstelle des Polymers können auch ein Gel (z.B. Silikongel), eine Flüssigkeit (z.B. Silikonöl, Polybutan, Esteröl, Fette), ein Gas (Luft, Stickstoff, SF6,...), ein Gasgemisch und/oder ein Glas treten.Nonlinear resistors with varistor behavior designed as varistor composites were produced by mixing polymeric material with a filler. Such mixing processes are well known from the prior art and need not be explained in more detail. The polymers can be thermosets, such as, in particular, epoxy or polyester resins, polyurethanes or silicones, or thermoplastics, for example HDPE, PEEK or ETFE. Instead of the polymer, a gel (e.g. silicone gel), a liquid (e.g. silicone oil, polybutane, ester oil, fats), a gas (air, nitrogen, SF 6 , ...), a gas mixture and / or a glass can also be used.
Alle Polymere aus Flüssigkomponenten, beispielsweise Epoxidharze, wurden vorgemischt und in Vakuum über den Füllstoff gegossen, so dass eine Infiltration stattfand. Die infiltrierten Proben wurden teilweise danach geschleudert, z.B. in einer Zentrifuge für 1/2 - 1 h bei 2000 Umdrehungen. Es konnten so erwünscht hohe Füllgrade von bis zu 60% erreicht werden. Thermoplastische Proben wurden durch Mischen des Füllstoffs zusammen mit dem Polymer, z.B. ETFE, vorgemischt und dann bei erhöhter Temperatur, z.B.280°C, bei Drücken von von mehreren, typischerweise 5 - 50, bar in eine Form gepresst.All polymers from liquid components, such as epoxy resins, were premixed and poured over the filler in a vacuum so that infiltration took place. Some of the infiltrated samples were then spun, eg in a centrifuge for 1/2 - 1 h at 2000 revolutions. In this way it was possible to achieve high filling levels of up to 60%. Thermoplastic samples were premixed by mixing the filler together with the polymer, eg ETFE, and then pressed into a mold at elevated temperature, eg 280 ° C, at pressures of several, typically 5-50, bar.
Der hierbei verwendete Füllstoff enthielt Varistorteilchen aus dotiertem Metalloxid mit überwiegend kugelförmiger Struktur, wobei die Teilchen aus kristallinen, durch Korngrenzen voneinander getrennten Körnern aufgebaut waren. Der Füllstoff wurde wie folgt hergestellt:The filler used here contained varistor particles made of doped metal oxide with a predominantly spherical structure, the particles being composed of crystalline grains separated from one another by grain boundaries. The filler was made as follows:
In einem konventionellen Sprühtrocknungsprozess wurde eine als wässrige Suspension oder Lösung vorliegende Varistormischung aus kommerziell erhältlichem ZnO, dotiert mit Oxiden von Bi, Sb, Mn und Co sowie mit Ni, AI, Si und/oder einem oder mehreren weiteren Metall(en), zu einem annähernd kugelförmige Teilchen aufweisenden Granulat verarbeitet. Das Granulat wurde in einem Kammerofen, z.B. auf einer mit ZnO beschichteten Al203-Platte, einer Pt- Folie oder einer ZnO-Keramik, oder gegebenenfalls auch in einem Drehrohrofen, gesintert. Die Aufheizzeiten beim Sintern betrugen bis zu 300 h, typischerweise z.B. 50°C/h oder 80°C/h. Die Sintertemperatur lag zwischen 900°C und 1320°C. Die Haltezeiten beim Sintern lagen zwischen 3h bis 72h. Nach dem Sintern wurde mit einer zwischen 50°C/h und 300°C/h betragenden Rate abgekühlt.In a conventional spray drying process, a varistor mixture of commercially available ZnO, doped with oxides of Bi, Sb, Mn and Co as well as with Ni, Al, Si and / or one or more other metals, was present as an aqueous suspension or solution processed approximately spherical granules. The granules were sintered in a chamber furnace, for example on an Al 2 O 3 plate coated with ZnO, a Pt film or a ZnO ceramic, or optionally also in a rotary tube furnace. The heating times during sintering were up to 300 h, typically for example 50 ° C / h or 80 ° C / h. The sintering temperature was between 900 ° C and 1320 ° C. The holding times during sintering were between 3 hours and 72 hours. After sintering, cooling was carried out at a rate between 50 ° C / h and 300 ° C / h.
Das solchermassen hergestellte Varistorgranulat wurde nachfolgend in einer Rüttelvorrichtung oder durch leichtes mechanisches Reiben getrennt. Durch Sieben wurden aus dem getrennten Granulat sodann Granulatfraktionen mit Teilchengrössen zwischen 90 und 160 μm, 32 und 63 μm und kleiner 32 μm hergestellt.The varistor granules produced in this way were subsequently separated in a vibrating device or by light mechanical rubbing. By sieving, granulate fractions with particle sizes between 90 and 160 μm, 32 and 63 μm and less than 32 μm were then produced from the separated granulate.
Varistorgranulate der verschiedenen Fraktionen wurden in bestimmten Gewichtsverhältnissen miteinander vermischt. Einigen dieser Mischungen und einigen der Fraktionen wurde ein Metallpulver mit geometrisch anisotropen, insbesondere schuppenförmig ausgebildeten, elektrisch leitfähigen Teilchen mit einem Dicken- zu Längenverhältnis von typischerweise 1/5 bis 1/100 zugemischt, z. B. Ni-flakes, deren Länge im Durchschnitt weniger als 60 μm betrug. Die Länge der Metallteilchen war in jedem Fall so gewählt, dass sie im Durchschnitt kleiner war als der Radius eines durchschnittlich grossen Teilchens des groben (90 - 160 μm) Varistorgranulats. Hierdurch und durch einen geringen Anteil, typischerweise 0,05 bis 5 Volumenprozent des Varistorgranulats, wurde die Ausbildung von metallisch leitenden Perkolationspfaden in der Mischung vermieden.Varistor granules of the different fractions were mixed together in certain weight ratios. Some of these mixtures and some of the fractions were mixed with a metal powder with geometrically anisotropic, in particular scale-shaped, electrically conductive particles with a thickness to aspect ratio of typically 1/5 to 1/100, e.g. B. Ni-flakes, whose length was less than 60 microns on average. In any case, the length of the metal particles was chosen so that on average it was smaller than the radius of an average sized particle of the coarse (90 - 160 μm) varistor granules. This and a small proportion, typically 0.05 to 5 percent by volume, of the varistor granulate prevented the formation of metallically conductive percolation paths in the mixture.
Die Ausgangskomponenten des Füllstoffs wurden im allgemeinen mehrere Stunden in einem Turbolamischer vorgemischt. War eine der Ausgangskomponenten das Metallpulver, so legten sich dessen Teilchen an die Oberflächen der kugelförmigen Varistorteilchen an, so dass besonders niederohmige Kontakte zwischen den einzelnen Varistorteilchen geschaffen wurden. Ausserdem fallen kleinere Teilchen ins Innere der zu einem kleinen Prozentsatz als Hohlkugel ausgebildeten Varistorteilchen und helfen so Stromführungsengpässe zu vermindern.The starting components of the filler were generally premixed in a turbo mixer for several hours. If one of the starting components was the metal powder, its particles lay against the surfaces of the spherical varistor particles, so that particularly low-resistance contacts were created between the individual varistor particles. In addition, smaller particles fall inside the varistor particles, which are designed as a hollow sphere to a small percentage, and thus help to reduce current supply bottlenecks.
Als metallischer Füllstoff sind auch feine Plättchen, leicht deformierbare, weiche Partikel und/oder Kurzfasern denkbar. Von Vorteil ist ein metallischer Füllstoff mit Teilchen, welche im Bereich der höchsten Verarbeitungstemperaturen aufschmelzen, sich bevorzugt in den Kontaktpunkten der Varistorteilchen ansammeln und dort zu einer verbesserten lokalen Kontaktierung führen.Fine platelets, easily deformable, soft particles and / or short fibers are also conceivable as metallic fillers. A metallic filler with particles that melt in the area of the highest processing temperatures, preferentially accumulate in the contact points of the varistor particles and lead there to an improved local contact is advantageous.
Ferner können als metallischer Füllstoff auch feine Pulver, etwa auf der Basis von Silber, Kupfer, Aluminium, Gold, Indium und deren Legierungen, oder leitfähige Oxide, Boride, Carbide mit Partikeldurchmessern vorzugsweise zwischen 1 und 20 μm verwendet werden. Die Teilchen dieser Pulver können ohne weiteres kugelförmig ausgebildet sein.Furthermore, fine powders, for example based on silver, copper, aluminum, gold, indium and their alloys, or conductive oxides, borides, carbides with particle diameters preferably between 1 and 20 μm can also be used as the metallic filler. The particles of these powders can easily be spherical.
Vor dem Zusammenführen von Matrixwerkstoff und Füllstoff sollten die im Füllstoff enthaltenen elektrisch leitfähigen Teilchen mit den Varistorpartikeln an deren Oberflächen verbunden werden. Es kann dann bei einem Matrixwerkstoff auf der Basis eines Polymers, wie etwa eines Epoxidharzes, der Gehalt an leitfähigen elektrischen Teilchen gering sein und einen unteren Wert von 0,05 Volumenprozent aufweisen.Before the matrix material and filler are brought together, the electrically conductive particles contained in the filler should be connected to the varistor particles on their surfaces. In the case of a matrix material based on a polymer, such as an epoxy resin, the content of conductive electrical particles can then be low and have a lower value of 0.05 percent by volume.
Eine solche Oberflächenverbindung kann mit Vorteil durch eine Wärmehandlung erreicht werden. Nach dem Mischen der Varistorpartikel und der elektrisch leitfähigen Teilchen haften diese Teilchen zwar zunächst gut an den Oberflächen der Varistorpartikel. Es hat sich aber gezeigt, dass beim nachfolgenden Zusammenführen, vorzugsweise Vermischen und Infiltrieren, mit dem Matrixwerkstoff, beispielsweise einem Polymer, einem Gel oder einem Öl, etwa auf der Basis eines Silikons, die elektrisch leitfähigen Teilchen zum Teil auf dem Matrixwerkstoff aufschwimmen und dann die dielektrische Festigkeit eines solchermassen hergestellen Widerstands ganz wesentlich beeinträchtigen. Durch mit der Wärmebehandlung eingeleitete Prozesse, insbesondere Diffusionsprozesse, werden die elektrisch leitfähigen Teilchen jedoch fest mit der Oberfläche verbunden. Beim nachfolgenden Zusammenführen (Vermischen, Infiltrieren) mit Matrixwerkstoffs wird ein Aufschwimmen der elektrisch leitfähigen Teilchen auf dem Matrixwerkstoff vermieden. Auch bei weiteren Misch- und Kompoundierschritten kann es nicht zu einer Umverteilung der elektrisch leitfähigen Teilchen kommen. Gegebenenfalls im wärmebehandelten Füllstoff vorhandene lose Teilchen können vor dem Zusammenführen mit dem Matrixwerkstoff vorzugsweise durch Waschen, Sieben oder Windsichten entfernt werden. Die für die Wärmebehandlung erforderlichen Temperaturen werden im wesentlichen durch den Werkstoff der elektrisch leitfähigen Teilchen bestimmt. Für Silber hat sich bei einer Behandlungszeit von ca. 3 h eine Wärmebehandlungstemperatur von ca. 400°C als ausreichend erwiesen. Höhere Temperaturen (bis 900°C) sind möglich, allerdings muss dann darauf geachtet werden, dass sich die elektrischen Eigenschaften der Varistorpartikel nicht zu stark ändern. Solche Änderungen könnten beispielsweise durch eine Reaktion des Werkstoffs der elektrisch leitfähigen Teilchen mit der Wismutphase der Varistorpartikel auftreten.Such a surface connection can advantageously be achieved by heat treatment. After the varistor particles and the electrically conductive particles have been mixed, these particles initially adhere well to the surfaces of the varistor particles. However, it has been shown that the following Merging, preferably mixing and infiltrating, with the matrix material, for example a polymer, a gel or an oil, for example based on a silicone, some of the electrically conductive particles float on the matrix material and then significantly impair the dielectric strength of such a resistance produced in this way . However, processes initiated by the heat treatment, in particular diffusion processes, firmly bond the electrically conductive particles to the surface. In the subsequent combination (mixing, infiltration) with matrix material, floating of the electrically conductive particles on the matrix material is avoided. Even with further mixing and compounding steps, there can be no redistribution of the electrically conductive particles. Loose particles which may be present in the heat-treated filler can preferably be removed by washing, sieving or air sifting before being combined with the matrix material. The temperatures required for the heat treatment are essentially determined by the material of the electrically conductive particles. For silver with a treatment time of approx. 3 h, a heat treatment temperature of approx. 400 ° C has proven to be sufficient. Higher temperatures (up to 900 ° C) are possible, however care must be taken to ensure that the electrical properties of the varistor particles do not change too much. Such changes could occur, for example, through a reaction of the material of the electrically conductive particles with the bismuth phase of the varistor particles.
Besonders geringe schädliche Reaktionen treten dann auf, wenn als elektrisch leitfähige Teilchen niedrigschmelzende feine Lotpartikel verwendet werden, und wenn die hierbei durch Adhäsion erzeugte Oberflächenverbindung gegebenenfalls noch bei niedrigen Temperaturen getempert wird.Particularly low harmful reactions occur when low-melting fine solder particles are used as the electrically conductive particles, and when the surface connection produced by adhesion is possibly also annealed at low temperatures.
Gute Oberflächenverbindungen werden auch dadurch erhalten, dass Varistorpartikel enthaltendes Pulver in einer metallhaltigen Lösung oder Dispersion dispergiert wird, und dass durch nasschemische Fällung der dispersen Lösung oder Dispersion oder durch elektrochemische oder galvanische Abscheidung die Oberflächenverbindung erzeugt wird. Durch nachfolgende Wärmebehandlung kann diese Verbindung noch gefestigt werden. Auch durch Dispersion eines Varistorpartikel enthaltendes Pulvers in einer metallhaltigen Lösung oder Dispersion, und durch nachfolgende reaktive Sprühtrocknung oder Sprühpyrolyse der dispersen Lösung oder Dispersion können feste Oberflächenverbindungen zwischen den Varistorpartikeln und den elektrisch leitfähigen Teilchen hergestellt werden. Ebenso ist eine Oberflächenbeschichtung aus der Gasphase möglich, wie dies mit Vorteil durch Sputtern, Aufdampfen oder Besprühen, etwa im Wirbelbett oder in einem Varistorgranulat- und gashaltigen Pulverstrom, erreicht wird.Good surface connections are also obtained in that powder containing varistor particles is dispersed in a metal-containing solution or dispersion, and in that the surface connection is produced by wet-chemical precipitation of the disperse solution or dispersion or by electrochemical or galvanic deposition. This connection can be strengthened by subsequent heat treatment. Solid surface connections between the varistor particles and the electrically conductive particles can also be produced by dispersing a powder containing varistor particles in a metal-containing solution or dispersion, and by subsequent reactive spray drying or spray pyrolysis of the disperse solution or dispersion. Surface coating from the gas phase is also possible, as is advantageously achieved by sputtering, vapor deposition or spraying, for example in a fluidized bed or in a powder stream containing varistor granules and gas.
Eine vorteilhafte Oberflächenbeschichtung wird auch durch Reibkontaktierung erreicht. Hierbei werden dem Varistorgranulat oder zumindest einem Teil davon und/oder der elektrisch leitfähigen Teilchen in einem Mischer Reibkörper aus dem Material den elektrisch leitfähigen Teilchen beigegeben und/oder es enthält die Auskleidung des Mischers Material der elektrisch leitfähigen Teilchen. Alternativ kann die Oberflächenbeschichtung auch durch Einbringen des Varistorgranulats und der elektrisch leitfähigen Teilchen in ein Mechano-Fusion-System erreicht werden, wie dies etwa von der Firma Hosokawa Micron Europe B.V., 2003 RT Haarlem, Holland vertreiben wird.An advantageous surface coating is also achieved by friction contacting. In this case, the varistor granules or at least a part thereof and / or the electrically conductive particles in a mixer are added with friction material made of the material to the electrically conductive particles and / or the lining of the mixer contains material of the electrically conductive particles. Alternatively, the surface coating can also be achieved by introducing the varistor granules and the electrically conductive particles into a mechano-fusion system, as is sold, for example, by Hosokawa Micron Europe B.V., 2003 RT Haarlem, Holland.
Gegebenenfalls, beispielsweise wenn die Matrix ein Silikon enthält, ist es von Vorteil, zumindest einen Teil des Varistorgranulats und/oder der elektrisch leitfähigen Teilchen mit einem Haftvermittler zu versehen. Die Haftfestigkeit des Füllstoffs in der Matrix ist dann optimiert. Solche Haftvermittler werden im allgemeinen in Form einer dünnen Schicht auf den Füllstoff aufgetragen. Geeignete Haftvermittler sind beispielsweise Silane, Titanate, Zirkonate, Aluminate und/oder Chelate. In diesem Fall können die elektrisch leitfähigen Teilchen auch dem Haftvermittler beigegeben werden und somit in wirtschaftlich besonders vorteilhafter Weise im selben Auftragsprozess mitverwendet werden.If necessary, for example if the matrix contains a silicone, it is advantageous to provide at least some of the varistor granules and / or the electrically conductive particles with an adhesion promoter. The adhesive strength of the filler in the matrix is then optimized. Such adhesion promoters are generally applied to the filler in the form of a thin layer. Suitable adhesion promoters are, for example, silanes, titanates, zirconates, aluminates and / or chelates. In this case, the electrically conductive particles can also be added to the adhesion promoter and can therefore be used in an economically particularly advantageous manner in the same application process.
Es wurden Widerstandskörper gefertigt, aus denen durch Sägen, Schleifen und Anbringen zweier Elektroden, etwa durch Beschichten mit einem Metall wie Gold oder Aluminium, Probewiderstände mit einem Volumen von einigen mm3 bis zu einigen dm3 realisiert wurden. Es wurden ferner auch Probekörper gefertigt, bei denen die Elektroden beim Vergiessen mit einem Giessharz, wie etwa einem Epoxy oder einem Silikon, direkt mitvergossen wurden. In der nachfolgenden Tabelle sind die Zusammensetzungen von vier dieser Probewiderstände angegeben, wobei D den Durchmesser der Teilchen des Varistorgranulats bedeutet.Resistor bodies were manufactured, from which test resistors with a volume of a few mm 3 to a few dm 3 were realized by sawing, grinding and attaching two electrodes, for example by coating with a metal such as gold or aluminum. Test specimens were also produced in which the electrodes were cast directly with a casting resin, such as an epoxy or a silicone. The following table shows the compositions of four of these test resistors, where D means the diameter of the particles of the varistor granules.
Widerstand Polymer FüllstoffResistance polymer filler
1 50 Vol% Epoxy 50 Vol% Varistorgranulat, D = 90 - 160 μm1 50 vol% epoxy 50 vol% varistor granules, D = 90 - 160 μm
2 45 Vol% Epoxy 48 Vol% Varistorgranulat, D = 90 - 160 μm 7 Vol% Varistorgranulat, D = 32 - 63 μm2 45 vol% epoxy 48 vol% varistor granules, D = 90 - 160 μm 7 vol% varistor granules, D = 32 - 63 μm
3 50 Vol% Epoxy 47,5 Vol% Varistorgranulat, D = 90 - 160 μm 2,5 Vol % Ni-flakes3 50 vol% epoxy 47.5 vol% varistor granules, D = 90 - 160 μm 2.5 vol% Ni-flakes
4 45 Vol% Epoxy 48 Vol% Varistorgranulat, D = 90 - 160 μm 5,5 Vol% Varistorgranulat, D = 32 - 63 μm 1 ,5 Vol % Ni-flakes4 45 vol% epoxy 48 vol% varistor granules, D = 90 - 160 μm 5.5 vol% varistor granules, D = 32 - 63 μm 1, 5 vol% Ni-flakes
Alle diese Widerstände wurden aus dem gleichen Ausgangspolymer und dem gleichen groben Ausgangsgranulat (D = 90 - 160 μm) gefertigt.All of these resistors were made from the same starting polymer and the same rough starting granulate (D = 90 - 160 μm).
Der Widerstand 1 war Stand der Technik.Resistor 1 was state of the art.
Im Unterschied zum Widerstand 1 wies der Widerstand 2 eine höhere Füllstoffdichte sowie zusätzlich noch einen ca. 15 Vol% des groben Ausgangsgranulats betragenden Anteil des zuvor beschriebenen, feinkörnigen Varistorgranulats (D = 32 - 63 μm) auf.In contrast to resistor 1, resistor 2 had a higher filler density and, in addition, an approximately 15% by volume of the coarse starting granules of the previously described fine-grained varistor granules (D = 32-63 μm).
Im Unterschied zu den Widerständen 1 und 2 wies der Widerstand 3 einen 5 Vol% am Füllstoff betragenden Anteil an elektrisch leitenden Ni-flakes auf.In contrast to resistors 1 and 2, resistor 3 had a proportion of 5% by volume of the filler in electrically conductive Ni-flakes.
Im Unterschied zu den Widerständen 1 bis 3 wies der Widerstand 4 sowohl einen ca. 10 Vol% des Füllstoffs betragenden Anteil des feinkörnigen Varistorgranulats als auch einen ca 3 Vol% betragenden Anteil an elektrisch leitenden Ni-flakes auf.In contrast to the resistors 1 to 3, the resistor 4 had both a portion of the fine-grained varistor granules amounting to approx. 10% by volume of the filler and an amount of electrically conductive Ni-flakes amounting to approx. 3% by volume.
An diesem/ier Widerständen wurden - wie aus der nachfolgenden Tabelle entnommen werden kann - die Durchbruchfeldstärke UB [V/mm], der Nichtlinearitätskoeffizient αB und die maximal aufgenommene Leistung P [J/cm3], ermittelt. Zur Bestimmung von UB und α wurde an die Widerstände eine variable Gleichspannung angelegt und wurden die Widerstände so elektrischen Feldstärken zwischen ca 5 und ca 500 [V/mm] ausgesetzt. In Abhängigkeit von der herrschenden Feldstärke wurde die in jedem der Widerstände fliessende Stromdichte J [A/cm2] ermittelt. Die so ermittelten Werte von U und J bestimmten die Strom-Spannungs-Kennlinien der Widerstände. Aus jeder der Kennlinien wurde die Durchbruchfeldstärke UB des zugeordneten Widerstandes bei einer Stromdichte von 1 ,3x10"4 [A/cm2] ermittelt. α8 wurde für jeden der Widerstände aus der Steigung der Tangente an die zugeordnete Strom-Spannungs-Kennlinie doppelt-logarithmisch in dem durch die Durchbruchfeldstärke UB bestimmten Punkt entnommen.The breakdown field strength U B [V / mm], the nonlinearity coefficient α B and the maximum power P [J / cm 3 ] were determined on this / ier resistors, as can be seen from the table below. To determine U B and α, a variable DC voltage was applied to the resistors and the resistors were exposed to electrical field strengths between approx. 5 and approx. 500 [V / mm]. Depending on the prevailing field strength, the current density J [A / cm 2 ] flowing in each of the resistors was determined. The values of U and J determined in this way determined the current-voltage characteristics of the resistors. The breakdown field strength U B of the associated resistor was determined from each of the characteristic curves at a current density of 1.3 × 3 "4 [A / cm 2 ]. Α 8 was doubled for each of the resistors from the slope of the tangent to the assigned current-voltage characteristic curve taken logarithmically at the point determined by the breakthrough field strength U B.
P wurde aus Stromimpulsversuchen ermittelt, bei denen die Widerstände in einer Prüfvorrichtung mehreren 8/20 μs Stromimpulsen mit Stromdichteamplituden bis zu 1 [kA/cm2] bei elektrischen Feldstärken bis zu 800 [V/mm] ausgesetzt waren.P was determined from current pulse experiments in which the resistors in a test device were exposed to several 8/20 μs current pulses with current density amplitudes up to 1 [kA / cm 2 ] at electrical field strengths up to 800 [V / mm].
Aus dieser Tabelle ist ersichtlich, dass sich die Widerstände 2 bis 4 gegenüber dem Widerstand nach dem Stand der Technik (Widerstand 1 ) sowohl durch einen grösseren Nichtlinearitätskoeffizienten αB als auch durch eine erhöhte Leistungsaufnahme P auszeichnen und dies bei gleichzeitig niedriger Durchbruchfeldstärke. Dies ist zum einen eine Folge der verbesserten Kontaktierung der einzelnen Varistorpartikel untereinander durch die zusätzlich in der Mischung enthaltenen elektrisch leitfähigen Teilchen und zum anderen eine Folge einer besonders hohen Dichte an Varistorpartikeln. Diese hohe Dichte ist durch ein Varistorgranulat entstanden mit zwei Fraktionen von Teilchen mit unterschiedlichen Grossen, von denen die Teilchen der ersten Fraktion grössere Durchmesser als die Teilchen der zweiten Fraktion aufweisen und im wesentlichen in Form einer dichten Kugelpackung angeordnet sind und die Teilchen der zweiten Fraktion die von der Kugelpackung gebildeten Lücken ausfüllen. Die Durchmesser der Teilchen der ersten Fraktion liegen vorzugsweise zwischen ca. 40 und ca. 200 μm. Zur Erzielung einer hohen Dichte ist es besonders günstig, wenn die Durchmesser der Teilchen der zweiten Fraktion ca. 10 bis ca. 50% der Durchmesser der Teilchen der ersten Fraktion betragen, und wenn der Anteil der zweiten Fraktion ca. 5 bis ca. 30 Volumenprozent des Anteils der ersten Fraktion beträgt.From this table it can be seen, that the resistors 2 to 4 with respect to the resistor according to the prior art (resistance 1) α both by a larger non-linearity coefficient B and are characterized by an increased power consumption P and the lower at the same time the breakdown field strength. On the one hand, this is a result of the improved contacting of the individual varistor particles with one another due to the electrically conductive particles additionally contained in the mixture, and on the other hand, it is a result of a particularly high density of varistor particles. This high density is created by a varistor granulate with two fractions of particles of different sizes, of which the particles of the first fraction have a larger diameter than the particles of the second fraction and are arranged essentially in the form of a dense spherical packing and the particles of the second fraction Fill in the gaps formed by the ball packing. The diameter of the particles of the first fraction are preferably between approximately 40 and approximately 200 μm. In order to achieve a high density, it is particularly favorable if the diameter of the particles of the second fraction is approximately 10 to approximately 50% of the diameter of the particles of the first fraction, and if the proportion of the second fraction is approximately 5 to approximately 30% by volume the proportion of the first fraction.
Es hat sich gezeigt, dass eine verbesserte Energieaufnahme erreicht wird, wenn mindestens eine weitere Fraktion von überwiegend kugelförmig ausgebildeten Teilchen vorgesehen ist, deren Durchmesser ca. 10 bis ca. 50% der Durchmesser der Teilchen der zweiten Fraktion betragen und beispielsweise Teilchen kleiner 32 μm aufweisen. Die Energieaufnahme und/oder andere Eigenschaften können zusätzlich verbessert werden durch spezielle stöchiometrische Zusammensetzungen und durch bestimmte Strukturen der einzelnen Fraktionen, durch Auswahl geeigneter elektrisch leitfähiger Teilchen und durch Anwendung vorbestimmter Bedingungen bei der Herstellung der Fraktionen, wie insbesondere beim Sintern. It has been shown that improved energy absorption is achieved if at least one further fraction of predominantly spherical particles is provided, the diameter of which is approximately 10 to approximately 50% of the diameter of the particles of the second fraction and, for example, particles smaller than 32 μm . The energy absorption and / or other properties can additionally be improved by special stoichiometric compositions and by certain structures of the individual fractions, by selection of suitable electrically conductive particles and by application of predetermined conditions in the production of the fractions, such as in particular during sintering.

Claims

P A T E N T A N S P R Ü C H E PATENT CLAIMS
1. Nichtlinearer Widerstand mit Varistorverhalten, enthaltend eine Matrix und einen in die Matrix eingebetteten, pulverförmigen Füllstoff, bei dem der Füllstoff ein gesintertes Varistorgranulat mit überwiegend kugelförmigen Teilchen aus dotiertem Metalloxid aufweist, welche Teilchen aus kristallinen, durch Korngrenzen voneinander getrennten Körnern aufgebaut sind, dadurch gekennzeichnet, dass der Füllstoff zusätzlich elektrisch leitfähige Teilchen umfasst, welche höchstens einen Teil der Oberflächen der kugelförmigen Teilchen bedecken, und/oder dass das Varistorgranulat mindestens zwei Fraktionen von Teilchen mit unterschiedlichen Grossen enthält, von denen die Teilchen der ersten Fraktion grössere Durchmesser als die Teilchen der zweiten Fraktion aufweisen und im wesentlichen in Form einer dichten Kugelpackung angeordnet sind und die Teilchen der zweiten Fraktion die von der Kugelpackung gebildeten Lücken ausfüllen.1. Nonlinear resistance with varistor behavior, comprising a matrix and a powder-like filler embedded in the matrix, in which the filler has a sintered varistor granulate with predominantly spherical particles of doped metal oxide, which particles are composed of crystalline grains separated from one another by grain boundaries, thereby characterized in that the filler additionally comprises electrically conductive particles which cover at most part of the surfaces of the spherical particles, and / or that the varistor granules contain at least two fractions of particles of different sizes, of which the particles of the first fraction have larger diameters than the particles of the second fraction and are arranged essentially in the form of a dense spherical packing and the particles of the second fraction fill the gaps formed by the spherical packing.
2. Widerstand nach Anspruch 1 , dadurch gekennzeichnet, dass die Durchmesser der Teilchen der zweiten Fraktion ca. 10 bis ca. 50% der Durchmesser der Teilchen der ersten Fraktion betragen.2. Resistor according to claim 1, characterized in that the diameter of the particles of the second fraction are about 10 to about 50% of the diameter of the particles of the first fraction.
3. Widerstand nach Anspruch 2, dadurch gekennzeichnet, dass die Durchmesser der Teilchen der ersten Fraktion ca. 40 bis ca. 200 μm betragen.3. Resistor according to claim 2, characterized in that the diameter of the particles of the first fraction are about 40 to about 200 microns.
4. Widerstand nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass der Anteil der zweiten Fraktion ca. 5 bis ca. 30 Volumenprozent des Anteils der ersten Fraktion beträgt.4. Resistor according to one of claims 1 to 3, characterized in that the proportion of the second fraction is about 5 to about 30 percent by volume of the proportion of the first fraction.
5. Widerstand nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass mindestens eine weitere Fraktion von überwiegend kugelförmig ausgebildeten Teilchen vorgesehen ist, deren Durchmesser ca. 10 bis ca. 50% der Durchmesser der Teilchen der zweiten Fraktion betragen.5. Resistor according to one of claims 1 to 4, characterized in that at least one further fraction of predominantly spherical particles is provided, the diameter of which is approximately 10 to approximately 50% of the diameter of the particles of the second fraction.
6. Widerstand nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass die im Füllstoff vorgesehenen, elektrisch ieitfähigen Teilchen ca. 0,05 bis ca. 5 Volumenprozent des Füllstoffes ausmachen. 6. Resistor according to one of claims 1 to 5, characterized in that the electrically conductive particles provided in the filler make up approximately 0.05 to approximately 5 percent by volume of the filler.
7. Widerstand nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, dass die elektrisch leitfähigen Teilchen geometrisch anisotrop ausgebildet sind.7. Resistor according to one of claims 1 to 6, characterized in that the electrically conductive particles are geometrically anisotropic.
8. Widerstand nach Anspruch 7, dadurch gekennzeichnet, dass zumindest ein Teil der elektrisch leitfähigen Teilchen plättchen- und/oder schuppenförmig ausgebildet ist und diese Plättchen und/oder Schuppen ein Dicken- zu Höhenverhältnis von ca. 1/5 bis 1/100 aufweisen.8. Resistor according to claim 7, characterized in that at least some of the electrically conductive particles are in the form of platelets and / or scales and these platelets and / or scales have a thickness to height ratio of approximately 1/5 to 1/100.
9. Widerstand nach Anspruch 8, dadurch gekennzeichnet, dass die Länge der Plättchen und/oder Schuppen durchschnittlich kleiner als der Radius der Teilchen der ersten Fraktion des Varistorgranulats ist.9. Resistor according to claim 8, characterized in that the length of the platelets and / or scales is smaller on average than the radius of the particles of the first fraction of the varistor granules.
10. Widerstand nach Anspruch 7, dadurch gekennzeichnet, dass zumindest ein Teil der elektrisch leitfähigen Teilchen als Kurzfasern ausgebildet ist.10. Resistor according to claim 7, characterized in that at least some of the electrically conductive particles are formed as short fibers.
11. Widerstand nach einem der Ansprüche 1 bis 10, dadurch gekennzeichnet, dass zumindest ein Teil des Varistorgranulats und/oder der elektrisch leitfähigen Teilchen mit einem Haftvermittler versehen ist.11. Resistor according to one of claims 1 to 10, characterized in that at least part of the varistor granules and / or the electrically conductive particles is provided with an adhesion promoter.
12. Verfahren zur Herstellung eines Widerstands nach Anspruch 1 , bei dem der Varistorpartikel und elektrisch leitfähige Teilchen enthaltende pulverförmige Füllstoff mit einem die Matrix bildenden Werkstoff zusammengeführt wird, dadurch gekennzeichnet, dass vor dem Zusammenführen die im Füllstoff enthaltenen elektrisch leitfähigen Teilchen mit den Varistorpartikeln an deren Oberflächen verbunden werden.12. A method for producing a resistor according to claim 1, in which the varistor particles and electrically conductive particles containing powdered filler are brought together with a material forming the matrix, characterized in that before the bringing together the electrically conductive particles contained in the filler with the varistor particles at the other Surfaces are connected.
13. Verfahren nach Anspruch 12, dadurch gekennzeichnet, dass die elektrisch leitfähigen Teilchen mit einem die Varistorpartikel enthaltenden Pulver durch Mischen zusammengeführt werden, und dass die hierbei gebildete Mischung bei Temperaturen wärmebehandelt wird, bei denen sich die Oberflächenverbindung bildet.13. The method according to claim 12, characterized in that the electrically conductive particles are combined with a powder containing the varistor particles by mixing, and that the mixture formed in this way is heat-treated at temperatures at which the surface connection forms.
14. Verfahren nach Anspruch 13, dadurch gekennzeichnet, dass als elektrisch leitfähige Teilchen Lotpartikel verwendet werden. 14. The method according to claim 13, characterized in that solder particles are used as the electrically conductive particles.
15. Verfahren nach Anspruch 13 oder 14, dadurch gekennzeichnet, dass nicht oberflächenverbundene, elektrisch leitfähige Teilchen vorzugsweise durch Waschen, Sieben oder Windsichten aus der wärmebehandelten Mischung entfernt werden.15. The method according to claim 13 or 14, characterized in that non-surface-bonded, electrically conductive particles are preferably removed from the heat-treated mixture by washing, sieving or air classifying.
16. Verfahren nach Anspruch 12, dadurch gekennzeichnet, dass ein Varistorpartikel enthaltendes Pulver in einer metallhaltigen Lösung oder Dispersion dispergiert wird, und dass durch nasschemische Fällung der dispersen Lösung oder Dispersion oder durch galvanische oder elektrochemische Abscheidung die mit den Oberflächen der Varistorpartikel verbundenen elektrisch leitfähigen Teilchen als Fällungs- oder Abscheidungsprodukt hergestellt werden.16. The method according to claim 12, characterized in that a powder containing varistor particles is dispersed in a metal-containing solution or dispersion, and that by wet chemical precipitation of the disperse solution or dispersion or by galvanic or electrochemical deposition, the electrically conductive particles connected to the surfaces of the varistor particles be produced as a precipitation or deposition product.
17. Verfahren nach Anspruch 16, dadurch gekennzeichnet, dass das Fällungsprodukt wärmebehandelt wird.17. The method according to claim 16, characterized in that the precipitation product is heat-treated.
18. Verfahren nach Anspruch 12, dadurch gekennzeichnet, dass ein Varistorpartikel enthaltendes Pulver in einer metallhaltigen Lösung oder Dispersion dispergiert wird, und dass durch reaktive Sprühtrocknung oder Sprühpyrolyse der dispersen Lösung oder Dispersion die mit den Oberflächen der Varistorpartikel verbundenen, elektrisch leitfähigen Teilchen hergestellt werden. 18. The method according to claim 12, characterized in that a powder containing varistor particles is dispersed in a metal-containing solution or dispersion, and that the electrically conductive particles connected to the surfaces of the varistor particles are produced by reactive spray drying or spray pyrolysis of the disperse solution or dispersion.
EP99915429A 1998-04-27 1999-04-23 Non-linear resistance with varistor behaviour and method for the production thereof Expired - Lifetime EP0992042B1 (en)

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DE19824104A DE19824104B4 (en) 1998-04-27 1998-04-27 Non-linear resistor with varistor behavior
DE19824104 1998-04-27
PCT/CH1999/000165 WO1999056290A1 (en) 1998-04-27 1999-04-23 Non-linear resistance with varistor behaviour and method for the production thereof

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JP2002506578A (en) 2002-02-26
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EP0992042B1 (en) 2005-08-31
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DE19824104A1 (en) 1999-10-28
US6469611B1 (en) 2002-10-22
CN1145981C (en) 2004-04-14
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DE19824104B4 (en) 2009-12-24
ATE303652T1 (en) 2005-09-15
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AU3404399A (en) 1999-11-16
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