JPH0474847B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a film capacitor, and more particularly to the structure of a metal thin film electrode provided on a plastic film.

Conventional Structure and Problems Aluminum and zinc have traditionally been used as metal thin film electrodes for metallized film capacitors. Briefly describing the characteristics of each, when aluminum is used, it has excellent self-healing properties, but a decrease in capacitance becomes a problem in continuous durability tests. Furthermore, when zinc is used, the capacitance decreases less than that of aluminum in continuous durability tests, but it has the drawback of being inferior in self-healing properties and leading to dielectric breakdown at lower voltages. In order to improve this, it has already been proposed to use, for example, a two-layer metal thin film electrode of zinc and aluminum, or an alloy of both, but it is difficult to take advantage of only the advantages of both. The reality is that it has not been put into full-scale practical use.

OBJECTS OF THE INVENTION An object of the present invention is to provide a film capacitor equipped with a novel metal thin film electrode that has excellent self-healing properties and exhibits less decrease in capacitance during continuous durability tests.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a film capacitor in which a plastic film is used as a main dielectric material and aluminum or an aluminum alloy is provided as a metal thin film electrode on the plastic film. A pair of single-sided metallized films, each of which is oxidized except for the peripheral portion where the end surface electrodes are provided, and whose oxide film layer has a thickness of 100 Å or more, is wound one on top of the other, or a double-sided metallized film having the oxide film layer. This method is characterized in that the film and the combined film are wound in an overlapping manner.

DESCRIPTION OF EMBODIMENTS The details of one embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a film capacitor according to the present invention. In other words, it shows a structure in which the surface of the metal thin film electrode 2 made of aluminum or aluminum alloy provided on the plastic film 1 is oxidized except for the peripheral area where the end face electrode is provided. There is an oxide film layer 3 with a thickness of 100 Å or more.
The surface of aluminum or aluminum alloy is
It is known that it is slightly oxidized in the atmosphere and protects the inside, but the thickness of this oxide film is said to be 10 to 20 Å, which is different from the oxide film layer referred to in the present invention. It is thin and easily attacked by active oxygen caused by partial discharge. 1st
For this reason, the oxide film formed in the atmosphere at room temperature is omitted in the figure.

One feature of the present invention lies in the structure of the metal thin film electrode, which is obtained by oxidizing the metal thin film electrode to form an oxide film layer. First, a metal thin film electrode with a uniform thickness is formed, and then oxidation with active oxygen is performed except for the peripheral area where the end face electrode will be formed.
As shown in the figure, the oxidized portion forms an oxide film layer 3, but the thickness of the metal thin film electrode 2 is reduced by the amount of metal consumed in the oxide film layer 3. As a result, the thickness of the metal thin film electrode 2 is thicker in the peripheral part forming the end face electrode, and the thickness of the metal thin film electrode 2 is thicker in the opposing part.
As the thickness of the metal thin film electrode 2 becomes thinner, the metal thin film electrode 2 becomes thinner and has a so-called end-reinforced electrode structure or stepped vapor deposition structure.
is obtained. Furthermore, when a film capacitor using aluminum metal thin film electrodes is subjected to a continuous durability test, the decrease in capacitance is due to active oxygen generated by partial discharge reacting with aluminum and converting it into aluminum oxide, an insulator. However, if a thick oxide film layer 3 is formed by treatment with active oxygen in advance, this oxide film layer 3 will act as a barrier, preventing the occurrence of partial discharge itself and the formation of the metal thin film electrode 2 due to active oxygen. Suppresses oxidation. As a result, the film capacitor according to the present invention can achieve both excellent self-healing properties and stability of capacitance during continuous durability tests.

FIG. 2 shows another embodiment of the invention. In this case, a double-sided metallized film and a laminated film are used, and the laminated film has an oxide film layer 5 on the surface of the plastic film 4, and the plastic film 4 is decomposed by the heat of partial discharge and active oxygen. I try to prevent it from happening. In the double-sided metallized film as well, an oxide film layer 3 is provided on the surface of the plastic film 1, which is considered to be exposed to partial discharge, so as to prevent the plastic from decomposing.

The structure of the present invention can also be obtained by first depositing a metal thin film electrode on a plastic film and then attaching a metal oxide by, for example, sputtering, but it is easier to partially oxidize the surface of the metal thin film electrode 2. In addition, an oxide film layer with few defects can be obtained.

Specific examples are shown below.

Example After aluminum was attached to one side of a polypropylene film having a thickness of 6 μm, the peripheral portion on the side where the end face electrode was to be provided was covered with a tape margin and oxidized.
Simply put, the oxidation method is glow discharge treatment under low pressure. The conditions are that the degree of vacuum is 1 to 5 Torr as indicated by a Pirani type vacuum gauge, the distance between the counter electrode and the metal thin film electrode is 3 to 30 mm, and the applied voltage is 300 to 300 m AC.
It is 800V. Note that it is easier to set the conditions by applying an AC half-wave voltage using a metal thin film electrode as an anode. Since oxygen in the treatment tank decreases as the metal thin film electrode is oxidized, fresh oxygen should always be introduced into the discharge section through a leak valve or the like. Although the thickness of the oxide film layer can also be changed by the discharge voltage and the distance between the electrodes, a method of changing the treatment time (the time during which the metallized plastic film is exposed to the discharge) is more productive. For example, the degree of vacuum is 2 Torr, the distance between the counter electrode and the metal thin film electrode is 20
mm and AC voltage of 700 V, if the metallized plastic film is not moved, the glow discharge will disappear when the thickness of the oxide film layer becomes several 100 Å.

A polypropylene film on which aluminum was vapor-deposited was continuously oxidized under the conditions described above, and then a pair was wound up to provide a zinc end face electrode. Lead wires were soldered to this film capacitor element, the element was housed in a case, and the element was sealed with epoxy resin to obtain a completed product. Test at 85℃,
A continuous durability test of 440V was conducted.

FIG. 3 is a diagram showing the results of a continuous durability test. D is a film capacitor with metal thin film electrodes that are not subjected to ordinary oxidation treatment, and the resistance value of the deposited film is
It is 3.5Ω/□. A, B, and C are film capacitors with oxidized metal thin film electrodes;
A and B are capacitors according to the present invention, and C is a capacitor not according to the present invention, and the thickness of the metal thin film electrode at the opposing portion is 3.5Ω/□ in terms of vapor deposited film resistance. Further, the thickness of the oxide film layer is A=400 Å, B=100 Å, and C=60 Å. The thickness of the oxide film layer was calculated from the capacitance by preparing a 5 mm square capacitor using the oxide film layer as a dielectric and assuming that the dielectric constant of the oxide film layer was 7. Note that if the thickness is less than 100 Å, it will not function as a capacitor, so this is an extrapolation based on the resistance value of the deposited film. In addition, the vapor deposition film resistance value of the metal thin film electrode before oxidation treatment is A
1.8Ω/□, B is 2.9Ω/□, and C is 3.1Ω/□.

As is clear from FIG. 3, in film capacitor D using conventional metal thin film electrodes, the capacitance decrease exceeds -4% before 1000 hours, whereas in film capacitors A and B according to the present invention, the capacitance decreases by more than -4% before 1000 hours. , the decrease in capacitance after 1000 hours is -1%, respectively.
Within this range, it is about -2% (for C, it is about -3%). However, C with a thin oxide layer
The slope becomes steeper after 1000 hours, and the capacitance decreases over time, whereas the oxide film layer
For film capacitors A and B of 100 Å or more, the decrease in capacitance is almost a straight line on a semi-logarithmic graph for at least 3000 hours, and tends to saturate over time.

Even when the film capacitors were disassembled and observed after the continuous durability test, film capacitors D and C showed many traces of oxidation of the circular metal thin film electrodes in the opposing parts, whereas film capacitors A and B according to the present invention showed many traces of oxidation on the circular metal thin film electrodes. Both their number and diameter are small.

Effects of the Invention As is clear from the above explanation, the film capacitor with the metal thin film electrode structure according to the present invention has excellent self-healing properties and a small decrease in capacitance during continuous durability tests, and has a higher potential gradient design. It is possible to do this, and its industrial potential is great.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of each embodiment of the film capacitor according to the present invention, and FIG. 3 is a diagram showing the results of a continuous durability test of the film capacitor according to the present invention and a conventional film capacitor. 1... Plastic film, 2... Metal thin film electrode, 3... Oxide film layer.

Claims (1)

[Claims] 1 Plastic film is the main dielectric material,
Aluminum or aluminum alloy is provided as a metal thin film electrode on the plastic film,
The surface of the aluminum or aluminum alloy is oxidized except for the periphery where the end electrodes are provided, and the oxide film layer has a thickness of 100 Å or more, and a pair of single-sided metallized films are wound on top of each other or the oxide film is coated. A film capacitor made by winding a double-sided metallized film and a laminated film in layers.