JPS6014499B2 - Manufacturing method for resin-clad plastic film capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a manufacturing method aimed at significantly improving the characteristics of a resin-clad plastic film capacitor.

The plastic film capacitor referred to here is a metallized film with aluminum vapor deposited on both or one side wrapped around an organic film (e.g., polyethylene terephthalate, polypropylene, etc.), and the end surface of the wound film is coated with metal spraying (metallic coating) such as zinc. ) to form an electrode lead-out part, then heat-treated at high temperature while pressing, and then attached a lead.
This figure shows a capacitor obtained with a resin exterior.

In particular, the feature of this plastic film capacitor using metallized film is that the electrodes are made of a thin vapor-deposited film layer, so even if an electrical weak point occurs in the dielectric film and leads to breakdown, it will not be damaged. It has a self-healing effect in which the vapor deposited film near the weak point is scattered by the destructive energy and the insulation is restored. By taking advantage of this feature, this type of capacitor can now be used even at very high electricians. Moreover, the manufacturing process has been greatly simplified, and the complicated work of conventional methods, such as long-term drying, impregnation, and capacitor assembly, has been greatly simplified, so this plastic film capacitor has come to be used instead of the conventional MP capacitor and foil type capacitor. It has become. However, due to the structure of this plastic film capacitor, there is a minute void layer between the metallized film surface and the dielectric film surface, and when used at a high potential level, a minute discharge (corona) occurs in the void layer. If this corona occurs from the perspective, it will eventually deteriorate the dielectric film and the vapor deposited film of the electrode will be scattered by the energy of the corona, reducing the capacitance.
It was considered a big problem.

Conventionally, as a countermeasure against this problem, various studies have been conducted on methods to suppress the occurrence of corona or methods that have less impact even if corona occurs. The former method is to prevent the generation of corona by coating the microporous layer in the capacitor element with a resin that has been impregnated with insulating oil in advance, or to prevent the generation of corona by increasing the internal pressure of the void layer in the capacitor element. A method of increasing the corona generation starting voltage by coating with resin (
For example, using a resin that generates gas during resin packaging,
Methods such as performing a series of steps for resin packaging under pressure have been adopted, but none of them have been sufficiently effective.

In other words, the void layer between the films is so small that even if the film is sufficiently impregnated with insulating oil, the insulating oil may be absorbed by the exterior resin, resulting in instability in terms of manufacturing and properties. Also,
In order to permanently pressurize the atmosphere surrounding the device, the long-term characteristics may be unreliable, considering the gas permeability of the exterior resin or the stability of the adhesion between the terminals and the exterior resin. It has many problems and is difficult in practice.
Next, the latter method, which has less influence even if corona occurs, is to use a dielectric film with a small yield rate to reduce the partial voltage applied to the gap layer, or to form an electrode. Efforts have been made to reduce the rate of scattering of the vapor deposited film by increasing the thickness of the lacquer film, but films with low dielectric constants have the disadvantage of increasing the volume of the capacitor, so it is difficult to use films that can be used as capacitor films. has limited characteristics. In addition, increasing the thickness of the deposited film requires a large amount of energy during the self-healing action, greatly deteriorating the dielectric film and lowering the breakdown value. The present invention provides effective means for solving these problems.

First, if we consider the mechanism of corona generation in more detail, we will find that the metallized film thickness is d, the void layer is da,
What is the yield rate of the film?V is the corona generation voltage of the air.
Assuming that a, the corona generation voltage VS of the capacitor is expressed by the following formula.

VS = Kishi (da + dl) In this formula, if we consider Va as being given by a passive curve, then da, which determines Vs, has a minimum value, and even if da is larger than that, it will still be small. Even though
VS becomes higher.

In other words, in order to increase the corona generation starting voltage, the gap layer between the films must be made sufficiently thick or thin.
Practically speaking, it is preferable to reduce the amount. For this reason, the current method is to apply strong tension to the metal film, roll it up, and press the capacitor element while heat-treating it at a high temperature. The pressing of the capacitor element became loose and a sufficient pressing effect could not be obtained, resulting in poor characteristics.

Therefore, the present invention aims to prevent this loosening and at the same time improve the characteristics.

That is, during the resin packaging process, which is the cause of loosening of capacitor elements, a voltage is applied between the electrodes to reduce Maxwell stress [
This is a method in which the capacitor element is kept strongly tightened by applying F=(kgoat;)2], and this state is maintained even when the resin hardens.

Furthermore, in the present invention, weak points between the films can be self-healed by applying a voltage, and the electrostatic capacity can also be stabilized. The figure shows the capacitance changes before and after the resin-clad plastic film capacitor A manufactured by the manufacturing method of the present invention and the capacitor 8 manufactured by the conventional method, and the capacitance change after applying a voltage of 250 VAC at a temperature of 70°C. A comparison is shown.

In addition, as a sample of the product of the present invention, a double-sided metallized film in which electrode metal was vapor-deposited on both sides of a polyethylene terephthalate film with a thickness of 5 mm and a width of 32 ribs, and a polypropylene film with a thickness of 5 mm and a width of 3 mm were alternately used. After stacking them and winding them around a large base drum, the end faces are metal sprayed with zinc to form electrode lead-out parts, subjected to high-temperature heat treatment, and the base capacitor cut off.
A multilayer capacitor element was obtained through a series of steps of attaching leads, and while applying 300 V DC to the element, the attached epoxy resin was cured at a temperature of 80° C. for 1 hour, and an exterior package was used. As is clear from the figure, in the conventional product, the capacitance before and after the resin packaging decreased by about 0.5%, but in the product of the present invention, there is almost no change in capacitance, and no loosening of the capacitor element occurs.

Furthermore, even when a continuous life test was conducted, it was found that the capacitance change due to corona was much smaller in the product of the present invention than in the conventional product. Furthermore, the present invention is particularly effective in laminated capacitors made of independent metallized films, compared to conventional multilayer capacitors in which only metalized films are wound. . As described above, according to the manufacturing method of the present invention, an excellent resin-clad plastic film capacitor with almost no change in capacitance can be obtained through a simple process of applying a voltage during resin-cladding.

[Brief explanation of the drawing]

The figure is a diagram showing a comparison of the capacitance change characteristics of a resin-clad plastic film capacitor manufactured by the manufacturing method of the present invention and a capacitor manufactured by a conventional manufacturing method.

Claims (1)

[Claims] 1. A method for manufacturing a resin-clad plastic film capacitor in which a capacitor element is constructed using a metallized film, the method comprising sheathing the capacitor element with a resin while applying a voltage to the capacitor element.