JPS5968919A - Polypropylene film condenser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitor that uses a polypropylene film (hereinafter referred to as PP film) irradiated with electron beams in an inert gas atmosphere as a dielectric layer, which has excellent voltage resistance and a high capacitance. This invention relates to a capacitor that has a large capacity and can be made smaller.

Today's electrical equipment has strong demands for higher voltage, larger capacity, and smaller size. There is also an increasing demand for capacitors to have increased capacitance and be made smaller. The capacitance of a capacitor is proportional to the permittivity (ε) of the dielectric and inversely proportional to the thickness, but there is a limit because reducing the thickness of the dielectric causes a decrease in withstand voltage (dielectric breakdown strength).

Conventionally, a typical film used as a dielectric material for capacitors is a PP film, but in order to increase the capacity and reduce the size of capacitors, there is a demand for dielectric materials with even higher voltage resistance. A known method for improving the voltage resistance of a PP film is to immerse the PP film in methyl methacrylate, irradiate it with an electron beam, and graft polymerize the methyl methacrylate onto the surface of the PP film (
Jitsukō 58-21410). However, since this PP film had methyl methacrylate, which has a polar group, graft-polymerized on its surface, it
It has a disadvantage that the dielectric loss (tan δ) is larger than that of a film.

In addition, a two-step operation of dipping treatment and electron beam irradiation must be performed, and since the electron beam irradiation is performed in air, there is a disadvantage that the polypropylene decomposes and deteriorates, making it brittle.

The inventor of this invention has made this invention as a result of intensive research under these circumstances, and the invention consists of a capacitor element in which a dielectric layer of polymeric film is laminated between electrode foils and wound. The present invention provides a polypropylene film capacitor characterized in that the polymer film is a polypropylene film irradiated with an electron beam in an inert gas atmosphere.

The capacitor of the present invention is characterized in that a PP film irradiated with an electron beam in an inert gas atmosphere is used as a dielectric.

The PP film used in the capacitor of the present invention has the same dielectric constant and voltage resistance as the graft polymerized PP film of the prior art, but has significantly lower dielectric loss.
Furthermore, it has the advantage that decomposition and deterioration of the VcPP film is significantly less. Furthermore, it has the advantage that it has the same dielectric constant and dielectric loss as the unirradiated PP film, and has high voltage resistance. Therefore, according to the present invention, a capacitor that is smaller in size, has high voltage resistance, and has a large capacity can be obtained.

As the PP film used in this invention, a PP film such as a biaxially stretched PP film conventionally used for capacitors is used, and its thickness is appropriately selected depending on the type of capacitor.

Electron beam irradiation to the shredded PP film is performed using nitrogen, helium,
Under an atmosphere of inert gas such as neon or argon,
The electron beam irradiation is carried out at room temperature, and examples of commonly used electron beam irradiation devices include electron beam accelerators such as transformer type, Bumpgra-7 type, and Kotscroft-Walton type. As the amount of electron beam irradiation increases, the dielectric strength of PP film increases, and the dielectric constant hardly changes, but on the other hand, the dielectric loss increases and the specific resistance (p) decreases, especially when the amount of irradiation increases. As it grows, it becomes brittle.
Therefore, there is an appropriate range for the electron beam irradiation amount, and the appropriate irradiation amount is selected depending on the type of capacitor, the type and thickness of the PP film, etc. For example, 22 μm thick biaxially stretched P
When using the entire P film, 0.5 to 5.0 Mr at room temperature
The electron beam irradiation amount at ad i is appropriate.

Next, this invention will be explained by experimental examples and examples, but this invention is not limited to this invention.

Fruit 1'1l (electron beam irradiation test on PP film) 22μ
Characteristics of a stretched PP film of 2 m thickness after being irradiated with an electron beam at approximately 25°C in air and in a nitrogen atmosphere were determined at 25°C.
It was measured at °C and shown in Tables 1 and 2.

Table 1 PP film irradiated with electron beam in air As is clear from the results in Table 1, irradiation with electron beam in air rapidly increases dielectric loss and causes the PP resin itself to decompose and deteriorate. It cannot be used for capacitors.

Table 2 Films irradiated with electron beams under nitrogen gas atmosphere As is clear from the results in Table 2, under nitrogen gas atmosphere approximately 2
When the electron beam is irradiated at 5°C and the dose is increased, the withstand DC voltage and current slope increases and the corrosion rate increases slightly, but
On the other hand, dielectric loss also increases and specific resistance decreases. This film became quite brittle at irradiation doses of 5.0 and 10.0 Mraa. Therefore, in the case of this PP film, it is shown that a range of approximately 5.0 M rad or less is appropriate as the irradiation dose. Also radiation 〃
The higher [ is, the less red the color is, so the irradiation dose is appropriately selected taking this point into consideration.

Next, an example of a capacitor manufactured using a PP film irradiated with an electron beam in a nitrogen gas atmosphere will be described.

Example 1 (Power capacitor) As shown in Figure 1 (cross-sectional view of the main part of the capacitor element),
A dielectric layer (2) consisting of 8 stacked 22 μm thick PP biaxially stretched films (1) irradiated with an electron beam at approximately 25°C in a nitrogen atmosphere.
) with aluminum electrode foil (3) in contact with the capacitor element impregnated with mineral oil (Class 5181 No. 1 electrical insulating oil). was created using. The characteristics of each capacitor, including a control product using a PP film that had not been irradiated with an electron beam, were measured at 25° C. and the results are shown in Table 3.

Table 8 * AOL... AC voltage potential gradient withstand when ACT-t (AC voltage time characteristics) is applied for a long time of 105 seconds.

×*Volume ratio... Capacity of capacitor = εX (ACL)"
, and compared with the one using unirradiated PP film as 100.

It can be seen that the capacitor using the electron beam irradiated PP film has the same dielectric constant as the control product, but has a higher ACL, so it can be significantly miniaturized in terms of volume ratio.

Example 2 (Dry capacitor) As shown in Figure 2, a 22 μm thick PP biaxially stretched film was irradiated with an electron beam at about 25° C. under a nitrogen atmosphere.
A capacitor element with an aluminum electrode foil (2) in contact with one layer was coated and molded with epoxy resin (a 16-layer dry capacitor was fabricated. The characteristics were measured and the results are shown in Table 4.

Table 4 It can be seen that the capacitors using electron beam irradiated PP films have the same dielectric constant as the control product but have a high AOL, so they can be significantly miniaturized in terms of volume ratio.

[Brief explanation of drawings]

FIGS. 1 and 2 are sectional views of essential parts of capacitor elements of an embodiment of a power capacitor and a dry capacitor of the present invention, respectively. (1), 111)...PP film irradiated with electron beam under nitrogen atmosphere, (2)...Dielectric of PP film (14
4, (3), 02... Aluminum electrode foil.

Claims (1)

[Claims] 1. A capacitor consisting of a capacitor element in which a dielectric layer of a polymeric film is laminated between electrode foils and wound, the polymeric film is exposed to an electron beam in an inert gas atmosphere. A polypropylene film capacitor characterized by being a polypropylene film irradiated with.