JPH0376770B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a power supply device, and more specifically, to a power supply device using a strontium titanate ceramic capacitor as a member of a high-frequency oscillation, resonance, or coupling electric circuit. [Prior art] Dielectric heating for high frequency drying of wood, resin, paint, food, clothing, etc., high frequency sewing machines for clothing, induction heating for induction hardening of steel, high frequency melting of metals, glass, etc. Ceramic capacitors are used in some of the power supply circuits for these applications. Ceramic capacitors are thermally and chemically stable, can be miniaturized, and have an extremely simple structure, making them easy to use at high frequencies. Normally, ceramic capacitors use ceramics such as forsterite, steatite, magnesium titanate, titanium oxide, and calcium titanate, but these ceramics have a low dielectric constant, so they can be used as a power source to some extent. In order to secure the output, the power supply device has to be larger. In recent years, there has been a demand for power supplies for the various uses mentioned above to be as large in output as possible or as compact as possible. In order to meet this demand, studies have been conducted on the use of ceramic capacitors whose dielectric material is barium titanate-based ceramics having a high dielectric constant, for example, as circuit members for power sources for the various uses mentioned above.
As a result, conventional high-permittivity ceramics have problems such as rapid temperature rise during use or inability to obtain the calculated power output when energized, and are limited to high-frequency, low-power ranges. I had no choice but to use it. The present inventors discovered that the cause of this is that these conventional high dielectric constant ceramics are ferroelectric, and by replacing them with paraelectric or less ferroelectric materials. The inventors have discovered that this problem can be overcome, and based on this knowledge, the present invention has been completed. [Problems to be Solved by the Invention] That is, the present invention provides a power supply device using strontium titanate-based ceramics as a ceramic capacitor and using the ceramic capacitor as a member of the circuit for high-frequency dielectric or high-frequency induction. It is something. In the present invention,
By using strontium titanate-based ceramics, the temperature rise during use, which is the problem mentioned above, can be reduced, and the power output when applying electricity can be obtained close to the calculated value. was able to achieve this goal. I would like to explain these in turn. The temperature rise during use of a ceramic capacitor can be suppressed as the high frequency dielectric loss of the ceramic is small. Previous forsterite series,
Ceramics such as steatite-based, magnesium titanate-based, titanium oxide-based, and calcium titanate-based ceramics with a high frequency dielectric loss of 0.1% or less have been put into practical use as circuit members for power supplies for the various uses mentioned above. On the other hand, ceramics need to have a high dielectric constant in order to increase the output power or downsize the power supply. It is difficult to find one, and at present, as mentioned above, we have no choice but to limit ourselves to the limited high-frequency, low-power range using conventional high-permittivity ceramics with large high-frequency dielectric loss. On the other hand, the present inventors have been researching strontium titanate-based ceramics, and recently it has become possible to use this ceramic with a high-frequency dielectric loss of 0.1% or less. As a result, for the first time, we succeeded in suppressing the temperature rise during use in the various applications mentioned above. Note that the high frequency dielectric loss of this ceramic can be reduced to 0.1% or less, and if the composition is appropriately selected, to 0.03% or less. Furthermore, the high-frequency dielectric loss is greatly related to the service life of the capacitor, and it is desirable that the high-frequency dielectric loss be as small as possible, which is also advantageous. Next, I would like to explain the power output when charging.
The output for each of the above-mentioned applications is proportional to the product of the square of the voltage applied to the ceramic capacitor used and the capacitance at the time of application. Therefore, in order to increase the power output, it is first necessary to increase the applied voltage. However, conventional high-permittivity ceramics have the disadvantage of a significant decrease in capacitance when a voltage is applied, and due to this disadvantage, conventional high-permittivity ceramics are difficult to use in a limited high-frequency, low-power range. I have no choice but to stay. In recent years, there has been a demand for the power supply output voltage to be as high as possible for the various power supplies mentioned above, and for reasons of circuit design, it is difficult to apply voltage up to the maximum capacity of the capacitor.
The improvement of the above-mentioned shortcomings has become an important task in this field as it is often required. The present inventors believe that this drawback is due to the fact that conventional high dielectric constant ceramics are ferroelectric; I found that there is a solution. In other words, conventional ceramics such as forsterite-based, steatite-based, magnesium titanate-based, titanium oxide-based, and calcium titanate-based ceramics have a negligible decrease in capacitance when electricity is applied, but the present invention The decrease in capacitance of strontium titanate ceramics when energized, i.e.,
The voltage dependence rate of capacitance voltage is kept to less than 1% per 1KV/mm dielectric thickness, which is extremely superior to high dielectric constant ceramics such as barium titanate, which have a much larger reduction rate. I can say that. In addition, the temperature characteristics are excellent, with the reduction rate of capacitance at 85°C being less than 20% relative to the capacitance at 20°C, and in addition, there is almost no change in dielectric constant (or capacitance) over time. There is. It is clear that conventional high dielectric constant ceramics, such as barium titanate ceramics, undergo extremely large changes over time and are not suitable as circuit members for the various uses mentioned above. Therefore, the power supply device of the present invention has a dielectric constant of 1050 to 1310, a dielectric loss of 0.1% or less, and a capacitance voltage dependence rate of 1 KV/mm per electric field of 1 KV/mm dielectric thickness, In addition, a strontium titanate ceramic capacitor is used in which the capacitance at 85°C decreases by 20% or less relative to the capacitance at 20°C. [Means for Solving the Problems] This invention provides strontium titanate 62.4~
72.3% by weight, bismuth oxide 7.1~11.9% by weight, titanium oxide 20.2~23.9% by weight, and magnesium oxide 0.4~
2.4% by weight, and consists of manganese, niobium,
Contains at least one additive component selected from oxides of metals selected from chromium, nickel, cobalt, and iron, clay materials, and oxides of rare earth elements, and has a dielectric constant of 1050 to 1310. It has a loss of 0.1% or less, a voltage dependence of capacitance of 1% or less per electric field of 1KV/mm dielectric thickness, and a reduction rate of capacitance at 85℃ relative to capacitance at 20℃.
This is a power supply device for dielectric or induction heating using a strontium titanate ceramic capacitor with a strontium titanate content of 20% or less. [Function] Even though the present invention has a relatively large dielectric constant, the high-frequency dielectric loss is small, so the temperature rise during use can be reduced, and the capacitance decreases when electricity is applied. It is. [Example] Next, the present invention will be explained in more detail with reference to Examples. Strontium titanate, bismuth oxide, titanium oxide, magnesium oxide, and the necessary additives are mixed in the weight ratio shown in Table 1, an appropriate amount of binder is added, and the mixture is press-formed into a disc with a diameter of 16.5 mm and a thickness of 1 mm. After that, it was fired at about 1200°C for 2 hours to obtain ceramics. The rare earth element oxides in the additive components are
It is added to further reduce dielectric loss, and for example, cerium oxide, lanthanum oxide, etc. are used. This addition amount is usually 0.01 to 10
Selected within the range of weight %. Also, manganese, niobium, chromium, nickel,
Cobalt and iron oxides and clay substances are added as mineralizers to form a sintered body with a dense structure, and the amount added is usually selected within the range of 0.1 to 0.5% by weight. . These ceramics are, for example, shown in Figures 1 and 2.
It is used as a ceramic capacitor with the structure shown in the figure. In FIG. 1, terminals 2 and 2' are fixed to both sides of a ceramic 1 through electrodes 3 and 3' by means such as soldering, and the entire surrounding area is covered with a synthetic resin 5 such as epoxy resin. ing. 4 is a connector. A ceramic capacitor having the shape shown in FIG. 1 was processed and its characteristics were measured. The results are shown in Table 1.

〔Effect of the invention〕

The power supply device according to the present invention uses strontium titanate, bismuth oxide,
Using strontium titanate ceramics consisting of titanium oxide and magnesium oxide, the relative dielectric constant is
1050~1310, dielectric loss 0.1% or less, voltage dependence of capacitance 1% per electric field of 1KV/mm dielectric thickness
with the following and for capacitance at 20℃
In order to feature a power supply device using ceramics with a capacitance reduction rate of 20% or less at 85℃,
As a power supply device for induction heating such as high-frequency sensing and high-frequency sewing machines, induction heating for high-frequency hardening, high-frequency melting, high-frequency welding, etc., it has become possible to increase the power output and downsize the power supply, and it has great industrial benefits. There is something.

[Brief explanation of drawings]

FIGS. 1 and 2 show cross-sectional views of ceramic capacitors for high frequency dielectric heating and induction heating used conventionally and in the present invention. FIG. 3 is a diagram showing the relationship of the voltage dependence rate to the applied voltage in an embodiment of the present invention. FIG. 4 is a diagram showing the change in capacitance with respect to temperature in the same embodiment of the present invention. FIG. 5 is a diagram showing the change in capacitance over time in the same example of the present invention.

Claims (1)

[Claims] 1 Strontium titanate 62.4~72.3% by weight, bismuth oxide 7.1~11.9% by weight, and titanium oxide 20.2~
23.9% by weight and 0.4-2.4% by weight of magnesium oxide, and selected from oxides of metals selected from manganese, niobium, chromium, nickel, cobalt and iron, argillaceous materials and oxides of rare earth elements. Contains at least one additive component, has a relative dielectric constant of 1050 to 1310, a dielectric loss of 0.1% or less, and a voltage dependence of capacitance of 1 KV/mm per electric field of dielectric thickness.
% or less, and a dielectric or induction heating power supply device using a strontium titanate ceramic capacitor, which has a capacitance reduction rate of 20% or less at 85°C relative to the capacitance at 20°C.