JPH0376773B2 - - 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 hardening of steel, high-frequency melting of metals, glass, etc., or induction heating for high-frequency melting, 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 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 by replacing them with paraelectric or less ferroelectric materials. The present 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,
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 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 achieve high output or miniaturization of power supplies, and among these high dielectric constant ceramics, those with high frequency dielectric loss of 0.1% or less are comparable to the various ceramics mentioned above. It is difficult to find such a power, and at present, as mentioned above, we have no choice but to limit ourselves to the limited range of low power at high frequencies using conventional high-permittivity ceramics with large high-frequency dielectric loss. On the other hand, the present inventors have been researching strontium titanate ceramics, but
These ceramics have recently become available with high frequency dielectric loss of 0.1% or less, and by using this ceramic, for the first time, it has been possible to suppress 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 drop in capacitance when electricity is applied, and due to this disadvantage, when using conventional high-permittivity ceramics, it is difficult to use limited high-frequency small power. I have no choice but to stay within range. recent years,
Regarding the various power supplies mentioned above, there is a desire to make the output voltage of the power supply as high as possible, and for reasons of circuit design, it is often necessary to apply voltage up to the maximum capacity of the capacitor. Improving these shortcomings has become an important issue in this field. 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, the conventional forsterite-based, steatite-based, magnesium titanate-based,
Ceramics such as titanium oxide and calcium titanate have a negligible drop in capacitance when charged, but the strontium titanate ceramic of the present invention exhibits a drop in capacitance when charged, i.e. , the voltage dependence rate of the capacitance voltage is 1KV/
It can be said that the reduction rate is kept below 0.5% per mm dielectric thickness, which is extremely superior to high dielectric constant ceramics such as barium titanate, which exhibits a much larger reduction rate. In addition, the temperature characteristics are excellent, with the reduction rate of capacitance at 85℃ compared to capacitance at 20℃ being 37% or less, and 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, in the power supply device of the present invention, the dielectric constant is 510 to 820, the dielectric loss is 0.02% or less, and the voltage dependence of capacitance is 1 KV/mm per electric field with a dielectric thickness.
A strontium titanate-based ceramic capacitor is used, which has a capacitance of 0.5% or less and a decrease rate of capacitance at 85°C relative to capacitance at 20°C of 37% or less. [Means for Solving the Problem] This invention consists of 20 to 35 mol% of strontium titanate, 5 mol% of lanthanum titanate, and 60 to 75 mol% of barium titanate, and contains manganese, niobium, chromium, nickel, and cobalt. Contains at least one additive component selected from oxides of metals selected from iron, argillaceous materials, and oxides of rare earth elements, and has a relative dielectric constant of 510 to 820 and a dielectric loss of 0.02%.
Below, titanium has a voltage dependence of capacitance of 0.5% or less per electric field of 1KV/mm dielectric thickness, and a reduction rate of capacitance at 85℃ relative to capacitance at 20℃ is 37% or less. This is a power supply device for dielectric or induction heating using a strontium oxide ceramic capacitor. [Function] Even though the present invention has a relatively small dielectric constant, the high-frequency dielectric loss is also small, so the temperature rise during use can be extremely reduced, and the capacitance decreases when electricity is applied. It's small. [Example] Next, the present invention will be explained in more detail with reference to Examples. Strontium titanate, lanthanum titanate, barium titanate, and necessary additives were mixed at the molar ratio shown in Table 1, an appropriate amount of binder was added, and the mixture was press-formed into a disk with a diameter of 16.5 mm and a thickness of 1 mm. Ceramics were then fired at approximately 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. The amount added is usually 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, lanthanum titanate, and barium titanate ceramics as a ceramic capacitor, has a dielectric constant of 510 to 820, a dielectric loss of 0.02% or less, and a voltage dependence rate of capacitance of 1 KV/mm. Electric field per dielectric thickness
0.5% or less, and the reduction rate of capacitance at 85℃ relative to capacitance at 20℃ is 37% or less. BACKGROUND OF THE INVENTION As a power supply device for induction heating such as heating or induction hardening, high frequency melting, high frequency welding, etc., it has become possible to increase the power output and downsize the power source, 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 between the voltage dependence ratio and the applied voltage in an embodiment of the present invention, and 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 20-35 mol%, lanthanum titanate 5 mol%, barium titanate 60-75 mol%
Consisting of mol%, manganese, niobium, chromium,
Contains at least one additive component selected from oxides of metals selected from nickel, cobalt, and iron, clay materials, and oxides of rare earth elements, has a relative dielectric constant of 510 to 820, and a dielectric loss of 0.02. % or less, voltage dependence of capacitance per electric field of 1KV/mm dielectric thickness
A power supply device for dielectric or induction heating using a strontium titanate ceramic capacitor, which has a capacitance of 0.5% or less and a capacitance reduction rate of 37% or less at 85°C relative to the capacitance at 20°C.