JPS637001B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a composition consisting mainly of titanium oxide, to which semiconducting elements such as antimony oxide and bismuth oxide are added, magnesium oxide as an additive, and calcium oxide. The present invention relates to a voltage nonlinear resistance material made of a sintered body added with. That is, the voltage nonlinear resistance material according to the present invention has a high voltage dependence of its resistance value, and its characteristics are caused by the sintered body itself, and it has excellent high-temperature continuous load life and pulse resistance characteristics. It is possible to stably provide an element that has a low varistor voltage suitable as a noise prevention element for a micromotor and has good noise cutting characteristics.

In recent years, with the rapid progress and spread of audio equipment, control equipment, and small power equipment, prevention of noise caused by small electric motors, protection from overvoltage, protection of relay contacts, etc. have become important issues. but,
Since these devices generally tend to be cheaper, this point needs to be taken into consideration when solving the above-mentioned problems.

Hitherto, known voltage nonlinear resistance materials include silicon carbide sintered varistors, selenium and cuprous oxide varistors, and zinc oxide sintered varistors.

By the way, the voltage-current characteristics of a varistor are generally expressed by the formula I=(V/C). Here, V is the voltage applied to the varistor, I is the current flowing through the varistor, and C is a constant corresponding to the voltage when a predetermined current flows. Further, the index α is a non-linear coefficient and can be obtained by the following equation.

α=10g ₁₀ (I ₂ /I ₁ ) / 10g ₁₀ (V ₂ /V ₁ ) where V ₁ and V ₂ are the given currents I ₁ and I ₂ respectively
is the voltage at .

A resistor with α=1 is a normal resistor that follows Ohm's law, and it can be said that the larger α is, the better the voltage nonlinearity is. It can be used as a guideline. Further, a desirable value for C varies depending on the use of the varistor, but in a varistor for low voltage, it is preferable that the C value is low and that a value suitable for the use can be easily achieved.

Among the known varistors used so far, silicon carbide varistors have a particle size of
It is manufactured by baking silicon carbide particles of around 100μ in clay, and its voltage nonlinearity is due to the voltage dependence of the resistance between particles, so the value of C is determined by the thickness of the varistor, that is, the grain boundary in the direction of current flow. It can be adjusted by changing the number. but,
In the case of low voltage applications, since the C value per grain boundary is high, the number of grain boundaries must be reduced, and reducing the number of grain boundaries causes a problem in that the withstand voltage property decreases. In addition, this material has a relatively small non-linearity index α of 3 to 7, and since the silicon carbide is hard, the mold used for molding suffers from severe wear and is difficult to form into a precise shape.

On the other hand, selenium and cuprous oxide-based varistors have the disadvantage that the nonlinearity index α is as small as 2 to 3, and the limiting voltage cannot be increased, so they cannot be said to be satisfactory materials.

Furthermore, zinc oxide varistors generally have a large nonlinear index α of 10 to 50, and the particle diameter can be made as small as about 10μ, so the voltage range is also 10 to 50.
It has the advantage of being able to convert to 1000V, but because the main component, zinc oxide, is chemically unstable, it suffers from economical deterioration due to nonlinearity, and it is also time-consuming and expensive to manufacture. There are drawbacks.

In order to improve these drawbacks of conventional varistors, a material was proposed in which antimony oxide and bismuth oxide were added as additives to titanium oxide and sintered. This has the advantage that the nonlinear index α is higher than that of silicon carbide-based varistors, selenium, or cuprous oxide-based varistors, and that a desired C value can be achieved without changing the α value. However, this method had the drawback that it was difficult to uniformly disperse antimony oxide and bismuth oxide, which are the components added into the sintered body, resulting in variations in quality.

For this reason, the present inventors have already developed a powder mixture of semiconductor elements such as antimony oxide and other raw materials in the form of a solution in order to overcome such drawbacks and develop voltage nonlinear resistance materials with stable quality. added to,
It is proposed that by sintering this, a product with stable quality can be obtained.

However, the method using such a solution has problems such as corrosion of manufacturing equipment and pollution, and the manufacturing cost is relatively high due to these countermeasures.

In addition, the addition of powders such as Sb results in non-uniform particle sizes, resulting in poor reliability and poor practicality, as well as weak mechanical strength, which tends to cause cracks during processing and assembly, resulting in poor yields. . In addition, cracks tend to occur during soldering, making it impractical.

In particular, when such a voltage nonlinear material is used as a noise prevention element for a micromotor with a varistor voltage of 10 V or less, the thickness of the element must be made thinner, which has the disadvantage of further weakening the mechanical strength. Ta.

When such a varistor is mounted on a motor, its reliability, so-called high-temperature load life, and pulse resistance are poor, and it cannot withstand long-term use, resulting in a shortened motor life.

The present invention improves such drawbacks, and contains bismuth oxide 0.05 to 10 mol% (in terms of Bi ₂ O ₃ ),
It is characterized in that 0.005 to 3% by weight (in terms of MgO) of magnesium oxide is added to a composition consisting of a trace amount of a semiconductor element and the remainder titanium oxide. Further, the present invention is characterized in that 0.005 to 3% by weight (calculated as CaO) of calcium oxide is further added to this composition.

In the present invention, as the titanium oxide raw material, bismuth oxide raw material, magnesium oxide raw material, and calcium oxide raw material, powdered titanium oxide, bismuth oxide, magnesium oxide, and calcium oxide are usually used. Substances capable of forming bismuth, magnesium oxide, calcium oxide can also be used. These are used as powders with an average particle size of about 5 to 300 μm.

In order to manufacture the voltage nonlinear resistance material of the present invention, a powder mixture is prepared by mixing, for example, a titanium oxide raw powder, a bismuth oxide raw powder, a magnesium oxide raw powder, and, if necessary, a calcium oxide raw powder in a predetermined ratio. A predetermined amount of a semiconducting element such as antimony oxide is added into the mixture and thoroughly mixed using a wet ball mill or the like. Next, after drying this mixture, it is calcined at a temperature of 800 to 1000°C, and this calcined body is crushed. A suitable binder such as polyvinyl alcohol, CMC, etc. is added to this pulverized material, formed into granules, and further press-molded into an appropriate shape and heated to a temperature of 1100 to 1400 in air or in an inert atmosphere.
Sinter at a temperature of °C. At this time, the temporary firing step can be omitted if it is not particularly necessary.

The material of the present invention contains a trace amount of a semiconducting element, Bi ₂ O ₃
The composition has a bismuth oxide content of 0.05 to 10 mol % when converted to 100 mol %, and the balance is titanium oxide (TiO ₂ ). The semiconductor element is antimony oxide (Sb ₂ O ₃ )
Niobium oxide (Nb ₂ O ₃ ), tantalum oxide (Ta ₂ O ₅ )
It is preferable that at least one of
If it is less than mol%, good nonlinearity cannot be obtained. Moreover, if this exceeds 0.074 mol %, no improvement in nonlinearity is particularly observed, and the nonlinearity in a high current region decreases.

On the other hand, if the bismuth oxide content is less than 0.05 mol% or more than 10 mol%, good nonlinearity cannot be obtained.

Also, magnesium oxide (MgO) 0.005% by weight
If the amount is less than 3% by weight, the particle size remains non-uniform, which is not preferable, and if it exceeds 3% by weight, the elements tend to stick to each other during firing, and the variation in varistor voltage increases as shown in FIG.

Calcium oxide (CaO) is added as a mineralizing agent to promote sintering of the sintered body, and if it is less than 0.005% by weight, it has no effect, while if it is more than 3% by weight, it will not be effective. , back,
This is not preferable because it causes deterioration of electrical characteristics. By adding calcium oxide (CaO), the present invention lowers the varistor voltage by 2 to 3 V when magnesium oxide (MgO) is added at 0.02% by weight or less, and further increases the strength of the ceramic body in this region, which in turn increases the varistor voltage. The aim is to create a synergistic effect that allows the device to be made smaller.

Since the voltage nonlinearity of the voltage nonlinear resistance material of the present invention depends on the sintered body itself, by changing the thickness in the direction of current flow, the desired C value can be obtained without changing the α value. It has the characteristic that it can be easily realized. In addition, since the C value per unit thickness is low, it is not only possible to easily produce devices for low voltage without weakening their mechanical strength, but also it is possible to easily obtain devices with uniform characteristics, which makes them durable. Reliability such as voltage characteristics can be significantly increased. Furthermore, since the α value can be made significantly larger than that of silicon carbide varistors, it has the advantage of being applicable to a wide range of applications.In addition, it has the advantage of being cheaper as it requires fewer types of raw materials. There is. Furthermore, the present invention has excellent characteristics against continuous high-temperature loads and pulsed voltage application.

In particular, the voltage nonlinear resistance material of the present invention has a
At a voltage as low as 30V, it is not only possible to increase the nonlinearity index α, but also to provide an extremely stable varistor voltage as shown in Figure 1, making it suitable as a noise prevention element for micromotors. be.

The noise in this micromotor is caused by the spark phenomenon that occurs between the commutator and the brushes. More specifically, in motors that generally use a commutator, the commutator is usually formed into a cylindrical shape with several commutator pieces attached at predetermined intervals, and there is always a space between each commutator piece. A gap occurs in the insulation layer. Therefore, when the commutator is rotating, the brush jumps through the gap between the commutator pieces and moves on to the next commutator piece, and during this jump, the coil is wound around the magnetic material. Due to the presence of a large self-inductance of the configured rotor, spike-like voltage sparks occur. These sparks cause electrical noise and tend to wear out the commutator and brushes, shortening the life of the motor.

By the way, this spike-shaped spark is a bipolar oscillating voltage, and its peak value is 20 to 20 degrees higher than the motor power supply voltage.
50 times, the connection time is approximately 100 μs, and it has high frequency components of 2 to 5 MHz, so in order to eliminate these, it is necessary to use a low voltage of 3 to 30 V and a nonlinearity index as large as possible as described above. In addition, a varistor element is required that has characteristics that can absorb high frequency components and eliminate these noises to near the operating voltage of the motor.

The voltage nonlinear resistance material of the present invention has all of these characteristics, and an element formed by providing electrodes thereon can be said to be very suitable for noise prevention in a micromotor. .
In this case, the electrode may be either non-ohmic or ohmic, as long as it does not impair the characteristics of the specified material, and any method such as baking, plating, vapor deposition, sputtering, thermal spraying, etc. may be used to attach the electrode. Can be used.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Titanium oxide powder (average particle size 10μ or less) in a ratio of Sb ₂ O ₃ 0.06 mol%, Bi ₂ O ₃ 0.5 mol% remaining TiO ₂
and bismuth oxide powder (average particle size 10 μ or less), add 0.005 to 50% of magnesium oxide (MgO).
It was added in an amount of 3% by weight and thoroughly mixed using a wet ball mill. Next, after drying this mixture, it was placed in an electric furnace and calcined for 30 minutes at about 1000°C.
After pulverizing this pre-fired product to a size that passes through 48 meshes, polyvinyl alcohol is added as a binder at a ratio of 2% based on the total weight, and after making it into granules, it is press-formed into a disc shape with a diameter of 16 mm and a thickness of 1.2 mm. did. Next, this molded body was fired at about 1300° C. for 1 hour to obtain a desired voltage nonlinear resistance material.

Silver baked electrodes were provided on both sides of the various materials thus obtained, and the varistor voltage characteristics were measured. The results are shown in FIG. As you can see from this table, the varistor voltage ranges from magnesium oxide 0.005 to
Not only is it extremely small in the range of 3% by weight, but it is also extremely stable despite slight variations in the amount of magnesium oxide added, making it suitable as a varistor for micromotors. Moreover, if the MgO is more than 3% by weight, the change in the varistor voltage (V/mm) becomes large, so the varistor voltage (V/mm) changes greatly due to a slight difference in the amount of MgO, which is not preferable because the yield of the product decreases.

When the sintered body thus obtained is observed under a microscope,
In the case where MgO is not added, the particle size of TiO ₂ varies widely. On the other hand, those containing 0.005% by weight or more of MgO have a more uniform particle size and have higher mechanical strength than those containing no MgO. If 0.005 to 3% by weight of CaO is further added to this, the varistor voltage can be lowered by 2 to 3V, especially when MgO is 0.02% by weight or less, compared to the case where CaO is not added, as shown by the dotted line in FIG.

Next, high temperature continuous load characteristics and pulse voltage application experiments were conducted on the voltage nonlinear resistance element thus obtained. Figure 2 shows the experimental results of high temperature continuous load characteristics, which were maintained in a constant temperature oven at 80°C with DC 10V applied for 0 to 1200 hours.

In Figure 2, A and B are Sb ₂ O ₃ 0.06mol%,
0.5% by weight of MgO is added to 0.5% by mole of Bi ₂ O ₃ and the remaining TiO ₂ , where A indicates V ₁₀ (voltage when 10 mA flows) and B indicates α.

C and D in Figure 2 are shown for comparison.
It has the same basic composition as A and B, but does not contain MgO. C indicates V ₁₀ and D indicates α.
The vertical axis shows the rate of change of V ₁₀ or α ΔV ₁₀ /V, Δα/
Indicates α. Thus, it can be seen that the material to which MgO is added has excellent high-temperature continuous load characteristics.
FIG. 3 shows a pulse voltage application experiment, and FIG. 4 shows the measurement circuit diagram. The number of pulses is 10 times each, and is performed by changing the switch SW shown in Figure 4. C is 0.1 μF, and the applied voltage E is
Measured in the range 250-1250V. In FIG. 3, E shows the data of the same composition as in FIG. 2, and F shows the data without MgO added for comparison.

From FIG. 3, it can be seen that adding MgO improves the pulse application characteristics.

Although antimony was used as the semiconductor element in this example, similar results were obtained using niobium, tantalum, or a composite thereof.

Example 2 Antimony oxide 0.05 mol%, bismuth oxide 0.5
Voltage nonlinear resistance material (A) with a composition of mol%, titanium oxide 99.45 mol% and magnesium oxide 0.5% by weight, Fe ₂ O ₃ based material (B), SnO ₂ based material (C), ZnO
A noise prevention element for a micromotor was created using the system materials (D) by providing electrodes on both sides of a sintered body made of these materials. Next, these noise prevention elements were attached between the coils of a micromotor for a working voltage of 5V, and the noise cut voltage was measured using an oscilloscope. FIG. 5 shows the state of noise cut for each sample. As is clear from this figure, the material (A) of the present invention exhibits superior properties compared to the materials (B), (C), and (D) used for conventional noise cutting.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between MgO addition and varistor voltage according to the present invention. Figure 2 shows the high temperature continuous load characteristics, Figure 3 shows the pulse application experiment,
FIG. 4 shows the experimental circuit of FIG. FIG. 5 is an oscillograph diagram showing the noise cutting state when the material of the present invention and the known material are used as a noise prevention element of a micromotor.

Claims (1)

[Claims] 1. Bismuth oxide 0.05 to 10 mol% (in terms of Bi ₂ O ₃ ),
Magnesium oxide 0.005 to 3
A voltage nonlinear resistance material characterized by containing additives in weight percent (MgO equivalent). 2. The semiconductor element is at least one of antimony oxide (in terms of Sb ₂ O ₃ ), niobium oxide (in terms of Nb ₂ O ₅ ), and tantalum oxide (in terms of Ta ₂ O ₅ ), and is in the range of 0.002 to 0.074 mol%. The voltage nonlinear resistance material according to claim 1, characterized in that it contains: 3 Bismuth oxide 0.05 to 10 mol% (in terms of Bi ₂ O ₃ ),
Magnesium oxide 0.005 to 3
Weight% (MgO equivalent) and calcium oxide 0.005-3
Voltage nonlinear resistance material containing added weight% (CaO equivalent).