DE2061728A1 - Electric capacitor and process for its manufacture - Google Patents

Description

DR.-ING. RICHARD GLAWE DIPL-ING. KLAUS DELFS DIPL-PHYS. DR. WALTER MOLL

MÖNCHEN HAMBURG MÖNCHEN

8 MÖNCHEN 26 2 HAMBURG 52

PO Box 37 WAITZSTR. 12th

LIEBHERRSTR. 20 TEL (C411) 89 22 55 TEL (0811) 22 05 48

YOUR SIGN YOUR MESSAGE FROM OUR SIGN MUNICH

A 15

REGARDS:

BRITISH OELIOPHANE LIMITED Bridgwater / England

Electric capacitor and process for its manufacture

The invention relates to an electrical capacitor in which a plastic film as a dielectric between conductive Elements is used, as well as a process for its manufacture.

In the manufacture of capacitors, it is known to use a flexible plastic film with suitable dielectric Properties, e.g. a polypropylene film, between two flexible metal foils, e.g. Aluminum foils, which represent the two conductive elements of the capacitor,

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arrange and combine together with another flexible Wind up the plastic film into a firm roll. The metal foils usually have laterally protruding Flaps that protrude from the end faces of the roll, namely the flaps belonging to the one film on the one side and the lobes belonging to the other polie the other side of the roller to allow connection to an electrical circuit. It is also general

Vaseline, common, the role with paraffin wax, petroleum jelly, one Mineral oil or chlorinated polyphenyl to soak around cavities which would otherwise contain air and lead to undesired corona discharges during operation.

With the development of very complex electronic equipment, a need has arisen for capacitors of higher capacitance with the same or smaller physical dimensions. This in turn makes thinner dielectric plastic films and metal foils thinner required 'A major problem in the production of such capacitors is to avoid small pores or openings, so-called "pin-holes", in the dielectric plastic film. Such "pin-holes" can cause discharges between the conductive elements or electrodes of the capacitor and thereby its complete destruction. Such "pinholes" are often formed during the production of thin plastic films.

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His way of overcoming this difficulty consists in the replacement of the metal foils by a metal layer made of, for example, aluminum or zinc, which through Vacuum coating is applied to one or both surfaces of the plastic dielectric sheet. For example a metal layer is applied to one surface of a dielectric plastic film in such a way that that they are across the lOlienstrip. until that extends a longitudinal edge, but stops at a distance from the other longitudinal edge. This coated film strip is then wound into a roll together with a similar strip of lOliene, but with the uncoated The edge of the other film at the opposite end of the roll is like the uncoated edge of the first film. at this arrangement, the two metal layers form the two conductive elements of the capacitor, which are separated with the two external connections by placing conductive material, e.g. zinc, on the end faces the roller is sprayed so that it makes contact with the turns of the metal layer that extends up to the relevant edge of the roll extends, manufactures. If such a capacitor has a "pin-hole" in the dielectric If plastic film occurs, it burns through the pinhole between the metal layers Discharge the metal layers in the vicinity of the "pin-hole"

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gone until the discharge is no longer sustained. Such capacitors are called "self-healing". However, such a self-healing discharge has the disadvantage that it contains oxidation and decomposition products Leaves "pin-holes" and in their vicinity, whereby the electrical properties of the capacitor deteriorate and its efficiency deteriorates. Further disadvantages of such a capacitor are the high cost of the metallization compared to the use of a metal foil, as well as the need for the metal plating very much precise control to ensure the ability to heal itself.

The object of the present invention is to provide an improved capacitor that is pinhole-free having dielectric plastic material between the conductive elements.

According to the present invention, in an electrical capacitor that has two pin-hole-free Plastic film has separate conductive elements as the dielectric, the plastic film serving as the dielectric produced by two films made of a plastic material which can be oriented by stretching with dielectric Properties laid on top of each other, the two foils

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until a state that can be orientated by stretching is reached heated and. then stretching in at least one direction to bring the two sheets together to form a single one coherent film to be connected or welded together.

In addition to such a capacitor, the invention relates to also the process for the manufacture of the capacitor, which is characterized in that one has two foils made of a plastic material with dielectric properties placed one on top of the other, heated the two films until they reach a state that can be oriented by stretching and then stretching in at least one direction in order to join the two films together to form a single film, wherein the film is then brought together with the two conductive elements.

The expression "stretch-orientable dielectric plastic material" is used herein to mean a synthetic one Plastic material understood which has an appropriate dielectric constant for use in a Has capacitor and which allows an at least partial orientation of its molecules by stretching. Examples such a material are polyolefins such as polypropylene and polyethylene, polystyrene, polyester,

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Polycarbonates, polysulfonates, polyphenylene oxides and non-plasticized polyvinyl chloride.

A "state which can be oriented by stretching" is to be understood as the state in which the plastic material experiences an at least partial molecular orientation when a train is applied to the material. This Condition occurs when the plastic material has a Temperature in the range between about 2 ° O below the crystalline Sohmeltespunktes or softening point and the transition temperature of the second order.

Since the two foils are bonded together to form a single foil, they are all in one Foil existing pin-holes covered by the layer of the other foil. The likelihood of two pin holes come to lie on top of each other in the two foils that they form a pin-hole in the composite foil is so small that that it can be neglected for practical purposes.

Advantageously, the film combination can be produced by a single plastic film in Cut lengthways along the center line and place the two foils on top of each other, i.e. double.

The film combination is preferably used both lengthways

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direction as well as in the transverse direction, either at the same time or one after the other. This gives the Composite film has balanced physical properties, making it easier to wind up and peel off.

In a preferred embodiment of the method according to the invention, the simple plastic film is made from of the two poles forming the composite film are produced, first stretched in the longitudinal direction while they are in a state that can be oriented by stretching is located, and then lätsjgs cut and doubled. The doubled pile is then stretched in the transverse direction while in a stretchable state is located, whereby the connection or weld to form a unitary composite film is obtained.

The amount of stretching to be performed on the doubled polie depends on a number of factors, including the initial thickness of the unstretched pile, the desired thickness of the composite film, the desired physical properties, e.g. the windability of the composite film, as well as the necessity, to ensure a complete bond between the stacked poles.

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The thickness of the composite film depends on the desired maximum operating voltage of the capacitor. S ^{1 For} general purposes, a film about 0.025 mm (1/1000 of an inch) thick can withstand a peak applied voltage of about 3000 volts. Thus, should for capacitors for an operating voltage of 230 volts AC (325 volts peak) are adapted, taking into account a sufficient safety distance, the thickness is preferably not less than about 0.005 mm (0.0002 inch) \ be.

In a preferred embodiment of the capacitor, two strips are made of the dielectric plastic film and the two conductive elements are wound together into a roll such that the turns of the conductive elements are separated from one another by the plastic film serving as a dielectric.

The two conductive elements can advantageously consist of a metal foil such as aluminum foil, and the capacitor can easily be manufactured in roll form by using a combination of metal foil, dielectric plastic film and metal foil laid one on top of the other in this order. Since the dielectric If the plastic film is free of pin holes, it is possible

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borrowed metal foil instead of the more expensive metal coatings because it is not necessary to provide a "self-healing ability" of the capacitor.

When it is desired to use metal layers as conductive elements, e.g. for downsizing

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the dimensions or for other reasons, this can be done in that a metal layer, for example made of aluminum or zinc, is applied by vacuum coating on one or both sides of the dielectric plastic film produced according to the invention. Since the ability to "self-heal" is not required, it is not necessary to provide the otherwise usual strict control of the thickness of the coating. Furthermore, such metal-coated capacitors can be used with impregnating agents, which would be unsuitable for self-healing capacitors, since they leave corrosive decomposition products behind. If the foil is metallized on one side, the capacitor can be manufactured in a known manner in such a way that two such foils, which rest with their foil surface against the metallized surface, are wound together to form a roll, so that they both in the roll Form conductive elements or electrodes, which are separated from one another by turns of one film thickness each. If the film is used on both sides to form the two

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the electrodes is metallized, the capacitor is made in such a way that the coated film with a second, uncoated, pin-hole-free plastic film will.

The capacitor can in a known manner with impregnating agents such as wax, mineral oil, petroleum jelly and chlorinated Polyvinyl are impregnated to avoid air-filled cavities, which otherwise lead to a corona discharge and a Failure of the capacitor could result.

An embodiment for the production of an inventive electric capacitor is described below.

EXAMPLE

An electrical capacitor consisting of a roll of two conductive elements made of aluminum foil, which were separated from one another by a dielectric in the form of a pin-hole-free polypropylene film was as follows manufactured.

A polypropylene film is produced by extrusion the molten polymer through a slot die to form

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a molten film of about 0.15 mm (0.006 inch) Thickness. The film was first quenched, and then passed over a series of heated rollers set at one temperature of about 115 ° 0 in order to bring the film into a state which can be oriented by stretching. the front rollers were driven at a higher peripheral speed than the rear rollers, so that the EiIm was stretched lengthways by about $ 40. The PiIm was then cut lengthways along the center line with a knife, and each leil was placed over a frame where one! Dell is placed on top of the other, i.e. was doubled. The two closely contacting foils were then placed in an oven at about 150 ° C The tensioning frame was guided and the film combination was stretched by 8ΟΟ5έ in the transverse direction. This connected the two Sheets intimately to form a uniform sheet about 0.01 mm (0.0005 inch) thick. The film was then on Cut open 7.5 cm wide and wound onto spools.

In a winder, a capacitor was made by winding a combination of at the same time a 70 mm wide aluminum strip, a strip of the polypropylene composite film 75 mm wide, a second Strips of aluminum foil with a width of 70 mm and a second strip of polypropylene composite foil with a width of 75 mm, in this order. During the Wickeins were between

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the metal foil and the plastic foil are conductive foil strips inserted at intervals at each end of the roll so that the strips which are in contact with the one film at one end of the roll and the strips in contact with the other film protruded from the other end of the roll. Each bundle of strips was gathered together and connected to a separate lead wire. The so The capacitor formed was then impregnated with paraffin wax and encapsulated in epoxy resin with the leads protruding at both ends.

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Claims (4)

Claims (y. Electrical capacitor with a dielectric made of plastic foil, characterized in that the dielectric consists of two foils lying on top of one another and connected to one another by stretching. 2. Capacitor according to claim 1, characterized in that the dielectric is composed of two stretched in one direction before connecting and then stretched together in the other direction and there. consists of connected foil. 3. A method of manufacturing an electrical capacitor by arranging one to serve as a dielectric Plastic film between two conductive elements, characterized in that the as Dielectric plastic film is produced in the Veise that you two films from orientable by stretching Plastic with dielectric properties laid one on top of the other, the foils laid one on top of the other until they are reached heated to a state orientable by stretching and then stretching them in at least one direction around them to connect to a pin-hole-free composite film. 109826/1579 4. The method according to claim 1, characterized in that there is a plastic film stretches in the longitudinal direction, then cuts it open in the longitudinal direction and the film halves placed on top of one another stretches in the transverse direction and thereby connects to a composite film. 109826/1579