JPH0376772B2 - - 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] Applications of induction heating such as high-frequency drying of wood, resin, paint, food, clothing, etc., high-frequency sewing machines for clothing, etc., or induction heating such as induction hardening of steel, high-frequency melting of glass, etc. , some ceramic capacitors are used in the power supply circuit. Ceramic capacitors are thermally and chemically stable. In addition to being compact, the structure of the capacitor is extremely simple, making it 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 power output as calculated when applying electricity, 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 that by replacing them with paraelectric or less ferroelectric materials, It was discovered that this problem could be overcome, and the present invention was completed based on this knowledge. [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,
The above problems arise due to the use of strontium titanate ceramics. In addition to reducing the temperature rise during use, the power supply output during energization could be obtained close to the calculated value, and furthermore, the various power supplies described above could be made larger in output or smaller in size. 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 smaller. 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 range of high frequency and low power using conventional high dielectric constant 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. Further, the high frequency dielectric loss is greatly related to the service life of the capacitor, and it is desirable that it be as small as possible, so it is also advantageous in this respect. Next, I would like to explain the power output when charging.
The output of the power supply for the above various uses 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. If you stay in the area, you won't get any money. 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,
Because it is often necessary to apply voltage to the maximum capacity of a capacitor,
Improvement of the above-mentioned shortcomings has become an important issue in this field. The inventors believe that the cause of this shortcoming is
We believe that this is due to the fact that conventional high dielectric constant ceramics are ferroelectric, but we have found that this problem can also be solved by using strontium titanate ceramics that are paraelectric or have a low degree of ferroelectricity. In other words, the conventional forsterite series,
Ceramics such as steatite-based, magnesium titanate-based, titanium oxide-based, and calcium titanate-based ceramics exhibit a negligible decrease in capacitance when energized. The drop in capacitance when the capacitance is applied, that is, the voltage dependence of the capacitance on voltage, is kept to less than 4% per 1 KV/mm dielectric thickness, and high dielectric materials such as barium titanate, which show a much larger reduction rate, It is said that this material is extremely superior to ceramics. In addition, the temperature characteristics are excellent, with the reduction rate of capacitance at 85°C being less than 10% 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 relative dielectric constant of 1170 to 1680, a dielectric loss of 0.1% or less, and a capacitance voltage dependence rate of 4% or less 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 10% or less relative to the capacitance at 20°C. [Means for Solving the Problems] This invention provides strontium titanate 31.0~
42.8% by weight, calcium titanate 13.6-18.6% by weight, lead titanate 15-24.5% by weight, bismuth titanate 26-30% by weight, 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 1170 to 1680. Loss less than 0.1,
The voltage dependence of capacitance is 4% or less per electric field of 1KV/mm dielectric thickness, and the reduction rate of capacitance at 85℃ relative to the capacitance at 20℃ is 10%.
This is a power supply device for dielectric or induction heating using the following strontium titanate ceramic capacitor. [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. There is. [Example] Next, the present invention will be explained in more detail with reference to Examples. Strontium titanate, bismuth titanate, calcium titanate, lead titanate, and the necessary additives are mixed in the weight ratio shown in Table 1, an appropriate amount of binder is added, and a disk with a diameter of 16.5 mm and a thickness of 1 mm is formed. After pressure molding, ceramics were obtained by firing at about 1200°C for 2 hours. The rare earth element oxide in the additive component is added to further reduce dielectric loss, and for example, cerium oxide, lanthanum oxide, etc. are used. This amount is usually
It is selected within the range of 0.01 to 10% by 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 titanate, lead calcium titanate, and lead titanate ceramics as a ceramic capacitor, and has a dielectric constant of 1170 to 1680 and a dielectric loss.
Ceramics with a voltage dependence of capacitance of 4% or less per electric field of 1KV/mm dielectric thickness, and a decrease rate of capacitance at 85℃ relative to capacitance at 20℃ of 10% or less Because the power supply device uses
BACKGROUND OF THE INVENTION As a power supply device for induction heating such as high frequency welding, it has become possible to increase the output power and downsize the power supply, which has great industrial benefits.

[Brief explanation of drawings]

FIGS. 1 and 2 are 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 Consists of 31.0-42.8% by weight of strontium titanate, 13.6-18.6% by weight of calcium titanate, 15-24.5% by weight of lead titanate, and 26-30% by weight of bismuth titanate, and contains manganese, niobium, chromium, nickel, cobalt and Contains at least one additive selected from oxides of metals selected from iron, clay materials, and oxides of rare earth elements, has a relative dielectric constant of 1170 to 1680, a dielectric loss of 0.1% or less, and a static Voltage dependence rate of capacitance: 4 per electric field of 1KV/mm 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 10% or less at 85°C relative to the capacitance at 20°C.