JP2012248716A - Metalized film capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metalized film capacitor with an excellent humidity resistance.SOLUTION: In the metalized film capacitor, at least one of metal vapor deposition electrodes 4a and 4b of a pair of metalized films 1 and 2 contains aluminum as a main constituent, and the surface thereof is formed with a MgAlOfilm. This arrangement prevents oxidation and capacitance change. The MgAlOfilm also has a high humidity resistance even with a thin film; thereby the film thickness of the metal vapor deposition electrode can be reduced while increasing the self-healing performance. As a result, the humidity resistance is enhanced and the withstand voltage performance is increased.

Description

  The present invention relates to a metallized film capacitor that is used in various electronic devices, electrical devices, industrial devices, automobiles, and the like, and is particularly suitable for smoothing, filtering, and snubbing of a motor drive inverter circuit of a hybrid vehicle.

  In recent years, from the viewpoint of environmental protection, all electric devices are controlled by inverter circuits, and energy saving and high efficiency are being promoted. In particular, in the automobile industry, hybrid vehicles (hereinafter referred to as HEVs) that run on electric motors and engines have been introduced into the market, and the development of technologies relating to energy saving and high efficiency has been activated, which is friendly to the global environment.

  Since such an electric motor for HEV has a high operating voltage range of several hundred volts, a metalized film capacitor having high withstand voltage and low loss electric characteristics is attracting attention as a capacitor used in connection with this electric motor. In addition, the trend of adopting a metallized film capacitor having a very long life is conspicuous from the demand for maintenance-free in the market.

  And this metallized film capacitor | condenser is divided roughly into what uses metal foil for an electrode generally, and the thing which uses the vapor deposition metal provided on the dielectric film for an electrode. In particular, a metallized film capacitor using an evaporated metal as an electrode (hereinafter referred to as a metal evaporated electrode) has a smaller volume occupied by the electrode than a metal foil, and can be reduced in size and weight. High reliability against dielectric breakdown due to self-healing function peculiar to metal-deposited electrodes (meaning the ability of the metal-deposited electrodes around the defect to evaporate and scatter and restore the function of the capacitor, generally called self-healing) Therefore, it has been widely used conventionally. The thinner the metal-deposited electrode is, the easier it is to evaporate and scatter, and the better the self-healing property, the higher the withstand voltage.

  FIG. 4 is a sectional view showing the structure of a conventional metallized film capacitor of this type, and FIGS. 5A and 5B are plan views showing a pair of metallized films used in the metallized film capacitor. is there. As shown in FIGS. 4 and 5, the metal vapor deposition electrode 101a and the metal vapor deposition electrode 101b are formed by vapor-depositing aluminum on one side of dielectric films 102a and 102b such as polypropylene film except for the insulation margins 103a and 103b at one end. Is formed. The metal vapor-deposited electrodes 101a and 101b are connected to metallicons 104a and 104b formed by spraying zinc at the opposite ends of the insulation margins 103a and 103b of the dielectric films 102a and 102b. The electrode is pulled out to the outside.

  Further, the metal vapor-deposited electrodes 101a and 101b are non-vapor-deposited having no metal vapor-deposited electrode formed by oil transfer on the side from the substantially central part of the width W of the effective electrode part forming the capacitance toward the insulation margins 103a and 103b. Are divided into a plurality of divided electrodes 106a and 106b by the slits 105a and 105b, and are positioned on the side opposite to the insulation margins 103a and 103b from the substantially central part of the width W of the effective electrode part and closer to the metallicons 104a and 104b. The dielectric films 102a and 102b are connected in parallel to the metal vapor-deposited electrodes 101a and 101b deposited on one surface of the dielectric films 102a and 102b by fuses 107a and 107b.

  The conventional metallized film capacitor configured as described above has a self-healing property and can realize a metallized film capacitor with less heat generation by the fuses 107a and 107b. In other words, the current passed through the metal vapor-deposited electrodes 101a and 101b increases as it approaches the metallicons 104a and 104b and decreases as it moves away. Therefore, since the fuses 107a and 107b and the divided electrodes 106a and 106b are provided on the side closer to the insulation margins 103a and 103b where the flowing current decreases, the heat generated in the fuses 107a and 107b due to the flowing current can be reduced, and the temperature rises. It was to be able to suppress.

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

JP 2004-134561 A

  Metallized film capacitors are prone to oxidative degradation due to moisture because the electrodes are very thin, and usually prevent moisture from entering with a resin sheath to ensure moisture resistance.

  In recent years, miniaturization of metalized film capacitors has been strongly demanded, and efforts have been made to reduce the thickness of the resin sheath. In particular, metalized film capacitors mounted on vehicles are often exposed to harsh high-temperature and high-humidity environments depending on the installation location, and since the withstand voltage is high, it is necessary to reduce the deposited film thickness. High moisture resistance is required.

  Therefore, an object of the present invention is to improve the moisture resistance of a metallized film capacitor.

In order to solve this problem, according to the present invention, at least one of the metal-deposited electrodes of the pair of metallized films is mainly composed of aluminum, and an MgAl ₂ O ₄ film is formed on the surface.

  The metallized film capacitor according to the present invention can exhibit excellent moisture resistance.

The reason is that by forming the MgAl ₂ O ₄ film on the surface of the metal vapor deposition electrode, the oxidation of the metal vapor deposition electrode can be suppressed and the change in capacity can be suppressed. Moreover, since the MgAl ₂ O ₄ film has high moisture resistance even if it is thin, the film thickness of the metal vapor deposition electrode can be reduced, and the self-healing property can be kept high.

  As described above, the present invention can improve moisture resistance without impairing the withstand voltage characteristics.

Sectional drawing which showed the structure of the metallized film capacitor in the Example of this invention (A), (b) The top view which showed the structure of the metallized film used for the metallized film capacitor in the Example of this invention The figure which shows the composition of the metal vapor deposition electrode in the Example of this invention Sectional view showing the structure of a conventional metallized film capacitor (A), (b) The top view which showed the structure of the metallized film used for the conventional metallized film capacitor

  Hereafter, the structure of the metallized film capacitor in the Example of this invention is demonstrated using FIGS. 1-2.

  FIG. 1 is a cross-sectional view showing the configuration of the metallized film capacitor of this example. FIGS. 2 (a) and 2 (b) are plan views of a pair of metallized films used in the metallized film capacitor of the present invention. FIG.

  In FIG. 1, the 1st metallized film 1 is a metallized film for P poles, and the 2nd metallized film 2 is a metallized film for N poles. Then, the first metallized film 1 and the second metallized film 2 are overlapped as a pair, and a metallized film capacitor is formed by using a plurality of turns wound as an element.

  As shown in FIG. 1, the first metallized film 1 has a metal vapor-deposited electrode 4a formed on one surface of a film 3a made of polypropylene serving as a dielectric. An insulating margin 5a is provided at the end portion to insulate the second metallized film 2.

  This metal vapor deposition electrode 4a is connected to the metallicon 6a to draw out the electrode. The metallicon 6a can be formed by, for example, zinc spraying, and is formed on the end face of the metal deposition electrode 4a.

  As shown in FIG. 2A, the metal vapor-deposited electrode 4a has a vertical margin 7a and a horizontal margin 8a (shown in FIG. 2) on the side from the approximate center in the width W direction of the effective electrode portion forming the capacitance toward the insulating margin 5a. (Shown) is formed. The vertical margin 7a and the horizontal margin 8a are formed by oil transfer, and the metal deposition electrode 4a is not deposited. As a result, the metal deposition electrode 4a becomes the large electrode portion 9a on the metallicon 6a side, and becomes the divided small electrode portion 10a divided into a plurality of portions by the vertical margin 7a and the horizontal margin 8a on the insulating margin 5a side.

  As shown in FIG. 2A, the divided small electrode portion 10a is electrically connected in parallel by a large electrode portion 9a and a fuse 11a, and adjacent divided small electrode portions 10a are also connected to the fuse 12a. Are electrically connected in parallel.

  Here, as shown in FIG. 2A, the large electrode portion 9a is formed on one surface of the film 3a from the substantially central portion of the width W of the effective electrode portion to the metallicon 6a. The width of each divided small electrode portion 10a is about 1/4 of the width W of the effective electrode portion, and is formed on one side of the film 3a from the substantially central portion of the width W of the effective electrode portion to the insulation margin 5a. The two divided small electrode portions 10a are provided from the substantially central portion of the effective electrode portion (width W) to the insulation margin 5a. However, the present invention is not limited to this, and a configuration in which three or more are provided may be employed.

  In the actual use, when a short circuit occurs in the defective part of the insulation, the metal vapor deposition electrode 4a around the defective part is evaporated and scattered by the short circuit energy, and the insulation is restored. With this self-healing function, the function of the metallized film capacitor is recovered even if a part between the first metallized film 1 and the second metallized film 2 is short-circuited. In addition, when a large amount of current flows through the divided small electrode portion 10a due to a defect in the divided small electrode portion 10a, the fuse 11a or the fuse 12a is scattered and the portion of the divided small electrode portion 10a in which the defect is caused is scattered. The electrical connection is broken and the metalized film capacitor current returns to normal.

  As with the first metallized film 1, the second metallized film 2 is a metal-deposited electrode except for one end of the insulation margin 5b on one side of a polypropylene film 3b serving as a dielectric, as shown in FIG. 4b is formed. However, the direction in which the second metallized film 2 and the first metallized film 1 are connected to the metallicon is different, and the second metallized film 2 is a metallicon 6a to which the first metallized film 1 is connected. Are connected to a metallicon 6b arranged opposite to the above. Further, the metal vapor deposition electrode 4b has a large electrode by a non-vapor deposition vertical margin 7b and a horizontal margin 8b which do not have a metal vapor deposition electrode on the side from the substantially central portion in the width W of the effective electrode portion forming the capacitance toward the insulation margin 5b. It is divided into a portion 9b and a plurality of divided small electrode portions 10b.

  As shown in FIG. 2B, the divided small electrode portion 10b has the same configuration as the divided small electrode portion 10a of the first metallized film 1, and is arranged in parallel by the large electrode portion 9b and the fuse 11b. In addition, the divided small electrode portions 10b are connected in parallel by the fuse 12b. The effect obtained by providing the divided small electrode portion 10b and the fuses 11b and 12b is the same as that of the first metallized film 1.

  In this embodiment, the metal vapor-deposited electrodes 4a and 4b are divided into large electrode portions 9a and 9b and divided small electrode portions 10a and 10b, but they function as capacitors even when they are not divided.

  In this embodiment, polypropylene films are used as the films 3a and 3b. However, polyethylene terephthalate, polyethylene naphthalate, polyphenyl sulfide, polystyrene, and the like may be used.

In the metallized film capacitor of this example, at least one of the metal vapor deposited electrodes 4a and 4b of the first metallized film 1 or the second metallized film 2 is mainly composed of aluminum, and an MgAl ₂ O ₄ film is formed on the surface. Is formed.

Example 1
The metalized film capacitor of Example 1 is configured as shown in FIG. 1 above, and aluminum and magnesium are used as electrode materials used for the metal deposition electrode 4a as the P pole and the metal deposition electrode 4b as the N pole. This alloy was used. In addition, the 1st metallized film 1 and the 2nd metallized film 2 of this Example 1 are formed from the same manufacturing method using the same electrode material and dielectric material (polypropylene film). Therefore, the characteristics of the metallized film of Example 1 described below are common to the first metallized film 1 and the second metallized film 2.

  A metal vapor deposition electrode made of an alloy of aluminum and magnesium can be formed, for example, by vapor deposition of aluminum and magnesium alternately or simultaneously.

Magnesium has a lower standard production energy of Gibbs per 1 mol of metal-oxygen bond than aluminum. Therefore, magnesium can be diffused on the surface of the deposited film by the degree of vacuum or oxygen introduction. Thus, metallized electrodes of the first embodiment, and a configuration in which MgAl ₂ O ₄ layer on the aluminum layer is formed.

  FIG. 3 shows the relationship between the depth (distance) converted value (nm) from the surface of the metal vapor deposition electrode and the atomic concentration (atom%) obtained from the X-ray photoelectron spectroscopy (XPS) analysis result. The depth conversion value from the surface of the metal vapor deposition electrode was converted from the comparison of the sputtering rate of the silicon dioxide film and the sputtering rate of aluminum under the same conditions. From this result, it can be seen that Mg is present in the surface layer in Example 1.

The presence of the MgAl ₂ O ₄ film is confirmed from the result of X-ray diffraction (XRD).

From these results, it is clear that the MgAl ₂ O ₄ film exists on the surface of the deposited film.

On the other hand, the metallized film capacitor for comparison used a metal vapor-deposited electrode on which only aluminum was vapor-deposited. An Al ₂ O ₃ film was formed as an oxide film on the surface of the metal vapor deposition electrode of this comparative example. This Al ₂ O ₃ film can be formed, for example, by vapor-depositing aluminum while introducing oxygen gas into the vapor deposition machine, or by oxidizing after vapor-depositing aluminum.

  A moisture resistance test and a short-time withstand voltage test were performed using the metalized film capacitors of Example 1 and Comparative Example.

The moisture resistance test was 85 ° C / 85% r. h. The capacitance change rate (%) of the capacitor after applying a voltage of 500 V for 900 hours under the conditions of high temperature and high humidity is obtained. That is, the rate of change in capacitance indicates (capacitor capacity C _t after voltage application−capacitor capacity C ₀ before voltage application) / C ₀ as a percentage (%).

In the short-time withstand voltage test, a sample metallized film and a reference metallized film were used, boosted by a constant voltage at a predetermined time in a 100 ° C. atmosphere, and a voltage (capacitance change rate of −5%) Withstand voltage) is measured, and withstand voltage is obtained from the voltage. The rate of change in withstand voltage is expressed as a percentage (%) of (sample withstand voltage V _t -reference withstand voltage V ₀ ) / V ₀ . As the reference metallized film, a metallized film in which aluminum was deposited without oxidizing the surface of the deposited film was used.

The above (Table 1) shows the thickness (nm) of the oxide film made of the MgAl ₂ O ₄ film in Example 1, the capacity change rate (%) in the moisture resistance test, and the withstand voltage change rate (%) in the short-time withstand voltage test. It shows the relationship. Table 2 shows the thickness (nm) of the oxide film made of the Al ₂ O ₃ film of the comparative example, the capacity change rate (%) in the moisture resistance test, and the withstand voltage change rate (%) in the short-time withstand voltage test. It shows the relationship. The film thickness of each oxide film was derived from the relationship between the amount of oxygen and the film thickness by cross-sectional observation of a scanning electron micrograph.

As can be seen from (Table 1) and (Table 2), in Example 1 using the MgAl ₂ O ₄ film, the capacitance change is suppressed even when the film thickness is small compared to the comparative example using the Al ₂ O ₃ film. It has excellent moisture resistance. Further, in Example 1, the thickness of the oxide film is 0.4 nm or more, and the capacity change rate is −10% or more, which has particularly high moisture resistance. In the comparative example, when the capacity change rate is set to −10% or more, the Al ₂ O ₃ film needs to be thickened to 20 nm or more. However, in Example 1, the moisture resistance can be improved with an oxide film thinner than 20 nm.

In Example 1, the thickness of the oxide film is 5 nm or less, and the withstand voltage change rate is −4% or more, which has particularly high withstand voltage. Even in the range where the thickness of the oxide film exceeds 5 nm, the voltage resistance is excellent as compared with the comparative example using the Al ₂ O ₃ film.

  As described above, Example 1 has better moisture resistance and voltage resistance than the comparative example when the thickness of the oxide film is less than 20 nm. Further, when the thickness of the oxide film is in the range of 0.4 nm or more and 5 nm or less, the capacity change rate is −10% or more and the withstand voltage change rate is −4% or more, and has particularly high moisture resistance and voltage resistance.

  The reason will be described below. That is, since magnesium reacts faster with water than aluminum, it reacts with moisture in the film to form an oxide film. For this reason, the water | moisture content in a film reduces and the oxidative degradation of a vapor deposition film is suppressed. Further, once the oxide film is formed, oxidation is less likely to occur, so that the insulation of the metal vapor deposition electrode can be suppressed and the change in capacity can be reduced.

  Therefore, by forming the metal vapor-deposited electrode with an alloy of aluminum and magnesium as in the first embodiment, an oxide film can be easily formed at the time of moisture absorption, capacity change can be suppressed, and moisture resistance can be improved.

Moreover, since the MgAl ₂ O ₄ film has high moisture resistance even if it is thin, the film thickness of the metal vapor deposition electrode can be reduced, and the self-healing property can be kept high.

  As described above, Example 1 can improve moisture resistance while maintaining withstand voltage characteristics.

Since magnesium has a higher reactivity with water than aluminum, the magnesium oxide film (MgO film) also has higher moisture resistance than the Al ₂ O ₃ film, but an oxide film made of an alloy of aluminum and magnesium (MgAl ₂ Since the O ₄ film is not deliquescent like the MgO film, the decrease in moisture resistance is small even when moisture is absorbed. Therefore, by forming the MgAl ₂ O ₄ film on the surface, higher moisture resistance can be realized.

The MgAl ₂ O ₄ film may be provided on either of the metal vapor deposition electrodes 4a and 4b, or may be provided on both, but it is particularly preferable that the MgAl ₂ O ₄ film is provided on the metal vapor deposition electrode 4a serving as the P electrode. Since MgAl ₂ O ₄ is insulative, it is difficult to anodize when a voltage is applied by providing it on the metal vapor deposition electrode 4a serving as the P electrode. In other words, it is possible to suppress the aluminum of the metal vapor-deposited electrode 4a from becoming insulating Al ₂ O ₃ and to suppress a decrease in capacity.

  The metallized film capacitor according to the present invention has excellent moisture resistance, and can be suitably used as a capacitor used in various electronic equipment, electrical equipment, industrial equipment, automobiles, etc., and particularly has high moisture resistance and high withstand voltage characteristics. This is useful in the field of automobiles that are required.

DESCRIPTION OF SYMBOLS 1 1st metallized film 2 2nd metallized film 3a, 3b Film 4a, 4b Metal vapor deposition electrode 5a, 5b Insulation margin 6a, 6b Metallicon 7a, 7b Vertical margin 8a, 8b Horizontal margin 9a, 9b Large electrode part 10a 10b Divided small electrode portion 11a, 11b Fuse 12a, 12b Fuse

Claims (3)

A pair of metallized films on which a metal vapor-deposited electrode is formed on a dielectric film, and the metal vapor-deposited electrodes formed on the pair of metallized films are overlapped so as to face each other through the dielectric film, or wound or Stacked elements,
It consists of a pair of metallicon electrodes formed on both end faces of this element,
At least one of the metal-deposited electrodes of the pair of metallized films is a metallized film capacitor in which aluminum is a main component and an MgAl ₂ O ₄ film is formed on the surface. The metallized film capacitor of claim 1, wherein the MgAl ₂ O ₄ film has a thickness less than 20 nm. The metalized film capacitor according to claim 1, wherein the MgAl ₂ O ₄ film has a thickness of 0.4 nm to 5 nm.

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