JPH0463530B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a metallized film capacitor,
More specifically, the present invention relates to a novel metallized film capacitor that is highly safe and does not cause smoke or ignition by simply reducing capacitance when used at temperatures exceeding the operating temperature. Conventionally, pressure type, temperature fuse, and current fuse have been considered as safety devices for capacitors, but pressure type safety devices, which require a metal case, are expensive, especially for resin-molded metallized film capacitors. Therefore, it is difficult to adopt. In addition, temperature fuses and current fuses have a low probability of operation considering the time and effort required to install them. In terms of temperature fuses, if the temperature fuse is installed near the point where it starts to break, the temperature fuse will operate at the beginning of the break, and the temperature fuse will stop before it reaches the point where it causes significant damage such as smoking and ignition. The reason is that if the capacitor works, but the point where it begins to fail is far from the temperature fuse, the metallized film capacitor will catch fire before the temperature fuse blows. Even with a current fuse, it is necessary to flow current in and out according to the capacitance, so it will not blow out with the minute pulse current at the initial stage of destruction. It is an object of the present invention to easily provide metallized film capacitors that do not smoke or catch fire, especially when destroyed at abnormal temperatures. The details of the present invention will be explained below using the drawings. FIG. 1 is a cross-sectional view of a metallized film capacitor. That is, double-sided metallized films 1 provided with metal thin film layers 2 and laminated films 3 are alternately stacked, and end electrodes 4 are provided at the ends. The characteristics of the present invention are that the melting point of the double-sided metalized film 1 is higher than the melting point of the laminated film 3, and that the tensile strength of the double-sided metalized film 1 is 250 Kg/cm ² or more at the melting point of the laminated film 3. .
According to this configuration, when a metallized film capacitor to which a voltage is applied is exposed to an abnormally high temperature, first, when the temperature of the laminated film approaches the melting point, dielectric breakdown of the laminated film continues to occur. At this time, the double-sided metallized film has a tensile strength of 250 kg/
cm ² or more, the metal thin film layer on the double-sided metallized film will only evaporate and scatter due to self-healing action, and the double-sided metallized film will not have holes. For this reason, the metallized film capacitor does not undergo through-breakage all at once, and its capacitance gradually decreases due to its self-healing action. As the capacitance decreases, the self-heating of metallized film capacitors decreases, so
For further destruction to occur, heat must be supplied from the outside. If the ambient temperature continues to rise, the capacitance will decrease to nearly zero, but smoke and ignition will not occur until the temperature approaches the melting point of the double-sided metallized film. The melting point of double-sided metalized film is 170℃ or higher even for polypropylene, 250℃ or higher for polyethylene terephthalate, and 200℃ for polycarbonate.
℃ or higher, which is well above the maximum operating temperature of ordinary metallized film capacitors, which is 70 to 100℃.
If the tensile strength of the double-sided metallized film is less than 250 kg/ ^cm2 at the melting point of the laminated film, holes will form in the double-sided metalized film when the laminated film undergoes dielectric breakdown near the melting point, and the metallized film capacitor will fail. Causes penetrating failure. That is, when the laminated film breaks down, the adjacent double-sided metallized film also causes dielectric breakdown at that point, and this happens one after another, so the speed of breakdown is faster than in the structure of the present invention.
Easy to cause smoke and ignition. This example applies when the conventional laminated film and the double-sided metallized film are made of the same material. The effects of the present invention will be described in more detail with reference to Examples below. Example 1 A double-sided metallized film was prepared by vapor-depositing aluminum on both sides of a polyethylene terephthalate film having a thickness of 6 μm to a sheet resistance of Ω/cm ² . A high-density polyethylene film with a thickness of 6 μm was used as the laminated film, and was wound so as to overlap the double-sided metalized film, and zinc was sprayed on both end faces to form a metalized film capacitor. After welding the lead wires, the capacitor was placed in a polyester resin case and sealed with epoxy resin to form a resin-molded metallized film capacitor. The properties of both of the above films are shown in the table below.

[Table] The test was conducted in an airless constant temperature chamber at 85°C by applying an overvoltage to the metallized film capacitor to destroy it. The results are shown in FIGS. 2 and 3. FIG. 2 shows the case where 325V AC is applied, and a current according to the capacitance flows when the voltage application starts. When measuring the temperature with a thermocouple embedded inside a metallized film capacitor, the temperature was 85°C before the start of charging.
The temperature, which was the same as the ambient temperature, rises over time and begins to rise rapidly when it reaches approximately 125°C. This corresponds to a decrease in current and thus a decrease in capacitance, and means that when the internal temperature rises close to the melting point of the laminated film, the capacitance decreases due to continuous self-healing action. ing. When the capacitance decreases, internal heat generation decreases and the temperature decreases, so further destruction does not occur. Since this destruction is a self-healing action, the case will not crack, molten material will not blow out from the case, and there will be no ignition or significant smoke. FIG. 3 is a diagram showing a case where an even higher overvoltage is applied. As is clear from the diagram, AC400V
Even when the capacitance was applied, no abnormal current was observed, only the capacitance decreased, and no cracking of the case, ignition, or significant smoke was observed. For example, if polypropylene (melting point 176°C), which is commonly used in the past, is used instead of the high-density polyethylene of the laminated film used in Example 1, the internal temperature will further rise when broken at AC325V to AC400V. This causes the case to crack, catch fire, and emit significant smoke.
The reason for this ignition and smoke is that the tensile strength of the double-sided metallized film is 230Kg/cm ² at the melting point of polypropylene, which is less than 250Kg/cm ² , which causes holes in the double-sided metalized film and the insulation. This is because it causes destruction. Example 2 Polyethylene terephthalate film, polycarbonate film, and reinforced polyethylene terephthalate film with a thickness of 6 μm (stretching ratio was changed to normal
120-130%, and annealed in an atmosphere at 100-120°C after stretching to improve the tensile strength at high temperatures), was deposited on both sides of a polyimide film to create a double-sided metallized film. A polypropylene film with a thickness of 6 .mu.m was used as the laminated film, and was wound so as to be overlapped with the double-sided metalized film, and zinc was sprayed on both end faces to form a metalized film capacitor. The characteristics of each of the above films are shown in the table below.

[Table] After making a resin-molded metallized film capacitor in the same manner as in Example 1, it was destroyed by applying AC350V in an airless constant temperature bath at 100°C. Case cracking, ignition, and significant smoke were observed during destruction only when the double-sided metallized film was polyethylene terephthalate film.In the case of reinforced polyethylene terephthalate film, polycarbonate film, and polyimide film,
As in Example 1, ignition or significant smoke did not occur due to only a decrease in capacitance. Furthermore, when the laminated film was a high-density polyethylene film similar to that in Example 1, none of the capacitors caught fire or emitted significant smoke. As is clear from the above embodiments, the present invention is a metallized film capacitor formed by winding or laminating a double-sided metallized film and a laminated film,
The melting point of the double-sided metalized film is higher than the melting point of the laminated film, and the tensile strength of the double-sided metalized film is 250 kg/cm ² or more at the melting point of the laminated film. It is possible to provide a highly safe metallized film capacitor that does not cause ignition or smoke by simply reducing the capacitance when used, and has great industrial potential.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the metallized film capacitor according to the present invention, and FIGS. 2 and 3 are diagrams showing the current and internal temperature when the metalized film capacitor according to the present invention is destroyed. DESCRIPTION OF SYMBOLS 1... Double-sided metallized film, 2... Metal thin film layer, 3... Laminated film, 4... Edge electrode.

Claims (1)

[Claims] 1. A metallized film capacitor formed by winding or laminating a double-sided metalized film and a laminated film, where the melting point of the double-sided metalized film is higher than the melting point of the laminated film, and the melting point of the double-sided metalized film is higher than that of the laminated film. The tensile strength of
A metallized film capacitor characterized in that it is Kg/cm ² or more.