JPH07161573A - Metalized film capacitor - Google Patents

Abstract

PURPOSE:To provide a metalized film capacitor so stable that the capacitance reduction is little during the applying of a withstanding voltage and continuous working. CONSTITUTION:A metalized film 12 is wound and covered with an covering film 11 to form a capacitor. The film 11 uses a material having higher linear expansion coefficient and thermal shrinkage ratio than those of the film 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to power factor correction for capacitors for electric power, capacitors for electric equipment, motor driving,
Alternatively, the present invention relates to a metallized film capacitor for electric circuits used for various power supply circuits.

[0002]

2. Description of the Related Art Conventionally, the exterior film of a capacitor element of this type of metallized film capacitor is of the following two types in order to prevent loosening of the metallized film on the outer periphery, in addition to the purpose of protecting the dielectric. Has been used.

(1) The exterior film 21 as shown in FIG.
Linear expansion coefficient ≧ linear expansion coefficient of the metallized film 22 and thermal shrinkage ratio of the exterior film 21 ≦ metallized film 22
The outer and metallized films 21 and 22 having the heat shrinkage ratio of 3 are wound to form a metallized film capacitor.

(2) The exterior film 31 as shown in FIG.
Coefficient of linear expansion ≦ linear expansion coefficient of metallized film 32, and thermal shrinkage of exterior film 31 ≧ metallized film 32
The metallized film capacitors 31 and 32 having the heat shrinkage ratio of 3 are wound to form a metallized film capacitor.

[0005]

However, in the above-mentioned structure, the following problems occur during aging which is a production process. In the case of (1), since the linear expansion coefficient of the exterior film is larger, the exterior film 21 shrinks more than the metallized film 22 when the temperature rises, the metallized film 22 is tightened by the exterior film 21, and the metallized film Although the air gap between the outer film 22 and the outer film 21 is suppressed, a gap 24 is formed between the outer film 21 and the outer film 21 in the step of returning the temperature to room temperature because the metalized film 22 has a higher heat shrinkage rate. (Fig. 2
reference). In the figure, 23 is a minute gap between the metallized films 22.

Contrary to (1), in the case of (2), the linear expansion coefficient of the metallized film 32 is larger when the temperature is raised,
Since the metallized film 32 shrinks more than the armored film 31, there is no effect that the metallized film 32 is tightened by the armored film 31, and the air gap 34 between the metallized film 32 and the armored film 31 and between the metallized films 22 is not. , 33 will occur. However, in the process of returning the temperature to room temperature, the heat shrinkage rate of the exterior film 31 is larger, so that the gap between the exterior film 31 and the exterior film 31 can be suppressed to some extent (see FIG. 3).

As shown in the above-mentioned conventional example, when the winding stress of the outer peripheral portion of the metallized film is weak and an air gap is generated between the metallized film and the exterior film, the self-gap in the air gap occurs during the withstand voltage test and the continuous durability test. There is a problem that the recovery action is promoted and the capacity is reduced.

The present invention solves such conventional problems, and an object of the present invention is to provide an excellent metallized film capacitor without a decrease in capacitance.

[0009]

To achieve the above object, the metallized film capacitor of the present invention has a linear expansion coefficient of the exterior film larger than that of the metalized film, and A material having a heat shrinkage ratio higher than that of the metallized film is used.

[0010]

In the above structure, since the linear expansion coefficient of the exterior film is larger than the linear expansion coefficient of the metallized film at the time of heating in the heat aging step in the production of the metallized film capacitor, the exterior film tightens the metallized film. In the process of returning the temperature to normal temperature, the outer film shrinks more than the metallized film, so the outer air gap is suppressed and the capacity is reduced. The reduction will be small.

[0011]

EXAMPLE An example of the present invention will be described below. In FIG. 1, 11 is an exterior film, 12 is a polypropylene film as a dielectric, and is a metallized film having a thickness of 6 μm.
The exterior film 1 is provided on the outer circumference of the wound metallized film 12.
1 is wound to form a capacitor element having a capacitance of 20 μF. In the figure, 13 and 14 are air gaps.

Here, the exterior film 11 is made of a material having a large linear expansion coefficient and a large thermal shrinkage ratio with respect to the metallized film 12. FIG. 4 shows the rate of change in capacity before and after a withstand voltage. The linear expansion coefficient of the exterior film of the example of the present invention> the linear expansion coefficient of the metallized film, and
A is a metallized film capacitor wound with both the exterior film and the metallized film, wherein the heat shrinkage rate of the exterior film> the heat shrinkage rate of the metallized film.

The exterior film and the metallized film, wherein the linear expansion coefficient of the exterior film of Conventional Example (1) ≧ the linear expansion coefficient of the metallized film and the thermal shrinkage rate of the exterior film ≦ the thermal contraction rate of the metallized film. B is a metallized film capacitor wound on both sides.

In the conventional example (2), the linear expansion coefficient of the exterior film ≦ the linear expansion coefficient of the metallized film, and the value shrinkage ratio of the exterior film ≧ the thermal shrinkage ratio of the metallized film. C is a metallized film capacitor wound with both films. Is.

As is apparent from FIG. 4, the capacity change rate of A of the embodiment is remarkably improved as compared with B and C of the conventional example. FIG. 5 shows the rate of change in capacity 1000 hours after a continuous durability test was conducted based on JIS4908. Note that A, B, and C in FIG. 5 have the same specifications as those in FIG. 4 described above.

In FIG. 5, A of the present embodiment is a conventional example B / C.
Compared with, the capacity decrease is less, and it is -0.5% after 1000 hours.
It stayed within the range and the result was very stable. In the above two tests, the decrease in capacitance of the metallized film capacitor of this example was small because the exterior film applied winding stress to the metallized film as the dielectric in the outer peripheral portion to suppress winding looseness, and It is believed that this is because the air gap between the film and the metallized film was suppressed, which suppressed the self-healing action and led to the suppression of the capacity decrease. In the examples, a polypropylene film was used as the metallized film, but instead of this, the same effect can be obtained with a polyethylene terephthalate film and a combination thereof.

[0017]

As is clear from the description of the above embodiments, the metallized film capacitor of the present invention is stable with less capacity reduction because the linear expansion coefficient and the thermal shrinkage ratio of the exterior film are larger than those of the metallized film. It is possible to provide the metallized film capacitor.

[Brief description of drawings]

FIG. 1 is a sectional view of an outer peripheral portion of a metallized film capacitor element according to an embodiment of the present invention.

FIG. 2 is a sectional view of an outer peripheral portion of a conventional metallized film capacitor element.

FIG. 3 is a sectional view of an outer peripheral portion of another conventional metallized film capacitor element.

FIG. 4 is a graph showing the rate of change in capacity before and after a withstanding voltage test.

FIG. 5 is a graph showing the change over time in the rate of change in capacity in a continuous durability test.

[Explanation of symbols]

 11 Exterior film 12 Metallized film

Claims (2)

[Claims] 1. A metallized film capacitor, characterized in that a material having a coefficient of linear expansion and a coefficient of thermal shrinkage larger than those of the metallized film is used as the exterior film. 2. A metallized film capacitor formed by winding different kinds of films, wherein a material having a coefficient of linear expansion and a coefficient of thermal shrinkage larger than those of other wound films is used as an exterior film. A metallized film capacitor characterized by that.