JPH0126523B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a capacitor that uses a polypropylene film (hereinafter referred to as PP film) that has been irradiated with electron beams in an inert gas atmosphere as a dielectric layer, and has excellent voltage resistance, large capacitance, and can be miniaturized. Regarding. 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 material,
Although it is inversely proportional to the thickness, there is a limit because reducing the thickness of the dielectric causes a decrease in withstand voltage (dielectric breakdown strength). Conventionally, the typical film used as a dielectric material for capacitors is PP film, but in order to increase the capacity and downsize capacitors, there is a demand for dielectric materials with even higher voltage resistance. PP
As a method to improve the voltage resistance of the film,
A known method is to immerse a PP film in methyl methacrylate and irradiate it with an electron beam to graft-polymerize methyl methacrylate onto the surface of the PP film (Japanese Utility Model Publication No. 53-21410). However, this PP film
Because methyl methacrylate, which has a polar group, is graft-polymerized on the surface, it has the disadvantage that the dielectric loss (tan δ) is larger than that of a PP film that has not been graft-polymerized. 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 such circumstances, and it 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 electron beams 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 the dielectric. The PP film used in the capacitor of this invention has the same dielectric constant and voltage resistance as the graft-polymerized PP film of the prior art, but the dielectric loss is significantly lower, and furthermore, the decomposition and deterioration of the PP film is significantly less. has advantages. It also has the advantage of having the same dielectric constant and dielectric loss as unirradiated PP film, and high voltage resistance. Therefore, according to the present invention, it is possible to obtain a capacitor that is smaller in size, has high voltage resistance, and has a large capacity. The PP film used in this invention is:
Biaxially stretched PP conventionally used for capacitors
A PP film such as a film is used, and its thickness is selected as appropriate depending on the type of capacitor. The PP film is irradiated with electron beams at room temperature in an atmosphere of an inert gas such as nitrogen, helium, neon, or argon. , Vandegraaf type, Kotsukucroft-Walton type, and other electron beam accelerators. As the electron beam irradiation dose increases, the PP film's dielectric strength increases and its dielectric constant hardly changes, but on the other hand, the dielectric loss increases and the resistivity (ρ) decreases, especially when the irradiation dose becomes extreme. As it grows, it becomes brittle. Therefore, there is an appropriate range for the amount of electron beam irradiation, and it depends on the type of capacitor, type of PP film,
An appropriate irradiation amount is selected depending on the thickness and other factors. For example, when using a biaxially stretched PP film with a thickness of 22 μm, an electron beam irradiation amount of 0.5 to 5.0 Mrad at room temperature is appropriate. Next, the present invention will be explained with reference to experimental examples and examples, but the present invention is not limited thereto. Experimental example (Electron beam irradiation test on PP film) A biaxially stretched PP film with a thickness of 22 μm was irradiated with an electron beam at approximately 25°C in air and in a nitrogen atmosphere, and its properties were measured at 25°C and shown in Table 1. It is shown in Table 2.

[Table] As is clear from the results in Table 1, when irradiated with electron beams in air, the dielectric loss increases rapidly and the PP resin itself decomposes and deteriorates, so it cannot be used in capacitors.

[Table] As is clear from the results in Table 2, when the electron beam is irradiated at approximately 25°C in a nitrogen gas atmosphere and the dose is increased, the withstand DC voltage and current slope increases and the dielectric constant increases slightly. However, on the other hand, the dielectric loss also increases,
Specific resistance decreases. This film became quite brittle at irradiation doses of 5.0 and 10.0 Mrad. Therefore, in the case of this PP film, the appropriate irradiation dose is approximately 5.0 Mrad or less. Furthermore, since the higher the irradiation dose is, the more uneconomical it is, the irradiation dose is appropriately selected taking this point into consideration. Next, PP was irradiated with an electron beam under a nitrogen gas atmosphere.
An example of a capacitor fabricated using a film will be described. Example 1 (Power capacitor) As shown in Figure 1 (cross-sectional view of the main part of the capacitor element), an electron beam was irradiated at approximately 25°C in a nitrogen atmosphere.
For power use, a capacitor element is impregnated with mineral oil (JIS Class 1 No. 1 electrical insulating oil) in which a dielectric layer 2 made of three 22 μm thick PP biaxially stretched films 1 is placed in contact with an aluminum electrode foil 3. Capacitors were fabricated using two types of PP films with different electron beam irradiation doses. Characteristics of each capacitor including a control product using PP film that has not been irradiated with electron beams at 25°C
The results are shown in Table 3.

[Table] It can be seen that capacitors using electron beam irradiated PP film have the same dielectric constant as the control product, but have a higher ACL, so they can be significantly smaller in terms of volume ratio. Example 2 (Dry capacitor) As shown in Figure 2, a 22 μm thick PP biaxially stretched film 1 was irradiated with an electron beam at about 25°C in a nitrogen atmosphere.
A dry capacitor was fabricated by covering and molding 11 capacitor elements with aluminum electrode foils 12 in contact with an epoxy resin. The characteristics of each capacitor were measured, including a control product using a PP film that had not been irradiated with electron beams, and the results are shown in Table 4.

[Table] It can be seen that capacitors using electron beam irradiated PP film have the same dielectric constant as the control product, but have a higher ACL, so they can be significantly smaller 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. 1,11...PP irradiated with electron beam under nitrogen atmosphere
Film, 2...Dielectric layer of PP film, 3,1
2...Aluminum electrode foil.

Claims (1)

[Scope of Claims] 1. A capacitor consisting of a capacitor element in which a dielectric layer of polymeric film is laminated between electrode foils and wound, wherein the polymeric film irradiates an electron beam under an inert gas atmosphere. A polypropylene film capacitor characterized in that it is an irradiated polypropylene film.