JPS6336130B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a multilayer capacitor.

Multilayer capacitors have become widely produced in recent years, especially as capacitors for electronic communications devices, because they offer higher productivity and uniform performance than conventional wound capacitors. However, wound type capacitors are still the mainstream among capacitors designed to have a high potential gradient, such as capacitors for low-voltage phase advancement. This is mainly due to the fact that the electrical insulation voltage at the cut surface of the multilayer capacitor is considerably lower than the electrical insulation voltage between the dielectric layers, and is unstable.

It is known that the electrical withstand voltage of the cut surface changes depending on the cutting conditions.In particular, the electrical insulation voltage of the cut surface changes depending on the cutting conditions. A common method is to improve electrical insulation breakdown voltage. However, this method has two drawbacks. One is that the dielectric layer near the cut surface is stretched and cut due to frictional heat, resulting in an increase in tan δ especially at commercial frequencies. Another drawback is that it is difficult to control frictional heat, so the range of cutting conditions is narrow and the cutting speed is slow.

It is an object of the present invention to provide a multilayer capacitor that does not have the above-mentioned drawbacks, that is, does not increase tan δ at commercial frequencies, has a fast cutting speed, and has a high electrical insulation breakdown voltage at the cut surface. Hereinafter, details of the present invention will be described using the drawings.

FIGS. 1 and 2 show a plan view and a partially sectional front view of a multilayer capacitor according to an embodiment of the present invention.
In other words, in a multilayer capacitor in which double-sided metallized dielectric layers 1 and dielectric layers 2 are alternately stacked, a protective film 3 is provided on each upper surface, and end face electrodes 4 are formed on the left and right sides as seen in the drawing, the cross section (as shown in the figure) A press plate 6 is provided on the top and bottom of the front) with a cushioning material 5 in between.
The upper and lower presser plates 6 have a structure in which the distance between the upper and lower presser plates 6 is reduced by turning a bolt 7, thereby compressing each dielectric layer at the cut surface. The object of the present invention can be achieved by compressing the cut surface of the presser plate 6, but it is also possible to compress the entire surface. In addition, in FIGS. 1 and 2, the presser plate 6 and the bolt 7 are used as a method for compressing the cut surface, but in the present invention, various methods conventionally used for compression, such as springs, air pressure, rubber, and heat shrinkage, are used. Materials etc. can also be used.

Examples are shown below.

Example A double-sided metallized polyester film with a thickness of 5 μm and a polypropylene film with a thickness of 5 μm were overlapped and wound 1000 times around a drum with a diameter of 200 mmφ.
After providing end face electrodes with metallicon on both ends,
It was removed from the drum and cut with a metal saw to produce a multilayer capacitor. As the protective film, seven layers of polyester film each having a thickness of 100 μm were used on the upper and lower sides. The metal saw used at this time had a diameter of 100mmφ, a thickness of 0.5mm, and a number of teeth of 72.
A carbide blade was used. The cutting conditions were a metal saw rotation speed of 1000 rpm and a cutting speed of 3 m/min.
min was used. The cut surface of the multilayer capacitor that is not compressed is designated as A, and the cut surface of the multilayer capacitor is 5 kg /
Let B be the compressed material with a pressure of cm ² , and the AC voltage is
Rate of change in capacitance after applying for 30 seconds (Δc/c)
compared. Note that the AC voltage was started at 200V and increased in 50V steps. The number of samples was 5 for each, and the average value is shown in the graph. This result is the third
As shown in the figure. As is clear from Fig. 3, in the conventional multilayer capacitor that does not compress the cut surface (dashed line A), the capacitance decreases by more than 1% when 250V is applied, but with the present invention, the capacitance decreases by more than 1% when the cut surface is compressed. In the case of a multilayer capacitor (solid line B) that is compressed, the capacitance decreases within 1% even when 450V is applied.
The difference in electrical insulation breakdown voltage between the cut surfaces is significant.

Note that the pressure to compress the cut surface varies slightly depending on the dielectric material and thickness, but it is 3 to 15
Kg/cm ² pressure is good. This is because if the pressure is low, sufficient adhesion between the layers cannot be achieved, and if the pressure is too high, the electrical insulation breakdown voltage of the dielectric layer itself will be reduced.

The commercial frequency tan δ of the multilayer capacitor according to the above embodiment is 0.10 to 0.15%, which is almost the same as the tan δ value of the wound type capacitor.
A cutting method in which the thin metal film on the dielectric layer is made into an island shape by heating the cut surface has the disadvantage that the tan δ is as high as 0.25 to 0.35%. In addition, in order to stably generate frictional heat, the cutting speed of the saw blade is 1m/min.
The following are commonly used:

The effect of compressing the cut surface is that the discharge between the metal thin films on the dielectric layers adjacent to each other at the cut surface is terminated only by scattering of the metal thin film near the cut surface, and does not extend to the inside of the dielectric layer. Yes, this effect is the third
This is obvious both from the diagram and from visual observation of the multilayer capacitor after voltage application.

The present invention can be expected to produce similar effects not only when used in the bare element state as shown in FIGS. 1 and 2, but also when used in resin, oil, or the like.

As clarified above, according to the present invention,
It is possible to provide a multilayer capacitor that does not increase tanδ, has a fast cutting speed, that is, a cutting speed of a saw blade, and has a high electric withstand voltage at the cut surface,
Its industrial potential is great.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a multilayer capacitor according to an embodiment of the present invention, FIG. 2 is a partially sectional front view thereof, and FIG. 3 is a diagram showing the capacitance when a voltage is applied to the multilayer capacitor according to the present invention. FIG. 3 is a diagram illustrating changes in comparison with those of a conventional multilayer capacitor. 1...Metalized dielectric layer, 2...Dielectric layer, 3...
...Protective film, 4... End face electrode, 5... Cushioning material, 6... Holding plate, 7... Bolt.

Claims (1)

[Claims] 1 In a multilayer capacitor formed by stacking a plurality of metallized dielectric layers or a metallized dielectric layer and a dielectric layer, the metallized dielectric layers are compressed against each other with respect to the metallized dielectric layer at the cut surface. A multilayer capacitor characterized by a structure that applies pressure in the direction of