JPH0363206B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a metallized film capacitor, and more particularly to a method for winding the same.

Conventional Structure and Problems Conventionally, metallized film capacitors have generally been wound in the atmosphere, but there has been a concept of winding them in a vacuum. One purpose of this is that in a vacuum, air resistance is reduced, reducing air entrainment that contributes to wrinkles and meandering during winding, and as a result, faster winding speeds are possible. It is. In addition, when the dielectric material was paper, it also served as a drying purpose.

On the other hand, the aging of metallized film capacitors is mainly due to the oxidation reaction of the metal thin film formed on the plastic film. When the conventionally required potential gradient is low (for example, 50V/μm), the change in capacitance over time is 1000V according to the JIS standard.
It was not so difficult to satisfy the level of 4% or less after a continuous durability test. On the other hand, in a design with a higher potential gradient, this change in capacitance over time cannot be ignored.
This tendency is particularly noticeable in metallized film capacitors that use thin metal films of aluminum, which have excellent self-healing properties under high potential gradients. After winding in the atmosphere and applying metal spraying to the element end face, the capacitor is
Even if the film was dried by heating in a vacuum for a long time, it was difficult to remove the air and oxygen trapped between the film layers. Furthermore, even if the film is wound in a vacuum, air and oxygen that enter between the film layers cannot be ignored with the method of taking the film out into the atmosphere and spraying it with metal. These may seem contradictory at first glance, but in the former case, shrinkage has already occurred at the edges due to heating by metal radiation, especially when the plastic film is a polypropylene film, and the winding has already occurred. In addition to the tension during rolling, air is trapped between the layers due to heat shrinkage. In the latter case, air entering between the layers cannot be removed by the tension applied during winding alone.

If everything from winding to metal spraying to the exterior process is done in an oxygen-free environment, it will be an extremely complicated process.

OBJECT OF THE INVENTION An object of the present invention is to reduce the change in capacitance over time during continuous durability tests of metallized film capacitors.

Structure of the Invention In order to achieve this object, the present invention performs only the winding process in a quasi-oxygen-free atmosphere, heat-treats the wound element in that atmosphere, takes it out into the atmosphere, and applies a heat treatment to the end face of the element. Since it is a metal sprayed product, when it is taken out into the atmosphere, it can quickly prevent air and oxygen from entering between the layers, so it is possible to prevent air from entering between the layers even during the exterior packaging process. It is.

Description of examples Examples are shown below.

Example 1 A polypropylene film having a thickness of 6 μm was metallized by vapor deposition of aluminum so that the sheet resistance was 4Ω/□, and then the pair was wound in a vacuum chamber. The degree of vacuum at this time is 10 ^-4 Torr, 10 ^-2 Torr,
It was changed to 1Torr, 100Torr, and 760Torr. Capacitor elements wound at each degree of vacuum were heated to 2 at 105°C.
After being heat-treated for several hours, it was taken out into the atmosphere and sprayed with zinc. After attaching lead wires, the capacitor was sealed in an aluminum case with bellows and impregnated with wax to form a metallized film capacitor with a protection device. The test was a continuous durability test in which AC420V was applied in a constant temperature bath at 85℃. The evaluation was based on the change in capacitance over time. The results are shown in solid lines in Figure 1. Note that the horizontal axis represents the degree of vacuum (Torr) at which the winding and heat treatment were performed, and the vertical axis represents the rate of change in capacitance (ΔC/C) in % after 1000 hours of continuous durability testing. This result shows that the effect is saturated if the degree of vacuum during winding and heat treatment is 1 Torr or less. Further, the case where only winding is performed in a vacuum chamber and heat treatment is omitted is shown by dotted lines in the same figure. In this case, the change in capacitance over time is slightly smaller than when winding in the atmosphere (760 Torr), but the effect is not large. Furthermore, the effect is saturated at vacuum degrees below 100 Torr.

Example 2 A polypropylene film having a thickness of 6 μm was metallized by vapor deposition of aluminum so that the sheet resistance was 4Ω/□, and then the pair was wound in a vacuum chamber. At this time, the vacuum level in the vacuum chamber is
10 ^-4 Torr, 10 ^-2 Torr, 1Torr, 100Torr, respectively.
After evacuation, nitrogen gas (N ₂ ) with a purity of 99.99% was introduced to each chamber to a pressure of 1.1 atm and sealed off.
As a result, even when the capacitor element that has been wound and heat-treated in the vacuum layer is taken out into the atmosphere again, the pressure in the vacuum layer is maintained at or above atmospheric pressure, so that air does not flow into the capacitor element. After heat-treating the wound elements in each atmosphere at 100℃ for 2 hours,
It was taken out into the atmosphere and zinc was sprayed. After soldering the lead wires, the capacitor was sealed in an aluminum case with bellows, the lid was fixed with curling, and the capacitor was impregnated with wax to form a metallized film capacitor with a protection device. The test was a continuous durability test in which AC420V was applied in a constant temperature bath at 70℃. As in Example 1, the evaluation was based on the change in capacitance over time. This result is shown in FIG. 2 as a solid line. Note that the horizontal axis indicates the degree of vacuum initially drawn before introducing nitrogen gas. This result is similar to Example 1, and if the vacuum is evacuated to 1 Torr or less before introducing nitrogen gas,
It can be seen that there is little change in capacitance over time. Also
Once the temperature is below 1 Torr, the effect is not much different from when it is drawn to a high vacuum. The dotted line shows the case where the heat treatment was omitted under a nitrogen atmosphere in a vacuum chamber, but the effect was more pronounced than in Example 1, in which winding was performed in a vacuum. However, even in this case, the effect is further enhanced by not only winding the film in an oxygen-poor atmosphere but also performing heat treatment. In the above example, a polypropylene film was used as the heat-shrinkable plastic film.
A similar effect can be obtained by using a heat-shrinkable plastic film such as polyester or vinyl chloride that shrinks by 30%.

Effects of the Invention As described above, the present invention can reduce the change in capacitance over time, which is the biggest problem in increasing the withstand voltage of metallized film capacitors, and has great industrial efficiency. It is what it is.

[Brief explanation of drawings]

Figure 1 shows the rate of change in capacitance when a metallized film capacitor manufactured according to the present invention was subjected to a continuous durability test for 1000 hours, and Figure 2 shows the rate of change in capacitance when a metallized film capacitor manufactured according to the present invention was subjected to a continuous durability test. FIG. 2 is a diagram showing the rate of change in capacitance when a film capacitor is subjected to a continuous durability test for 1000 hours.

Claims (1)

[Claims] 1. A metallized film in which a metal thin film is formed on a heat-shrinkable plastic film is wound up in a vacuum of 1 Torr or less, and then the wound capacitor element is heat-treated to heat-shrink the ends. A method for manufacturing a metallized film capacitor, which comprises the steps of: removing the metallized film capacitor from the atmosphere, and then spraying metal onto the end face of the element. 2. A metallized film formed by forming a metal thin film on a heat-shrinkable plastic film is rolled up in a vacuum chamber evacuated to 1 Torr or less, an inert gas is introduced into this vacuum chamber to a pressure exceeding atmospheric pressure, and then A method for manufacturing a metallized film capacitor, which comprises heat-treating a wound capacitor element to heat-shrink the end portion, taking it out into the atmosphere, and spraying metal onto the end face of the element.