JPS637003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has a composition that is mainly composed of titanium oxide and contains semiconducting elements such as antimony oxide and bismuth oxide, and further contains silicon dioxide and calcium oxide as additives. The present invention relates to a voltage nonlinear resistance material made of a sintered body. 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=log ₁₀ (I ₂ /I ₁ )/log 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 use, 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 100 μ in size with clay, and its voltage nonlinearity is due to the voltage dependence of the resistance between particles. It can be adjusted by changing the number. However, 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, the nonlinear index α of this item is also 3 to 7.
It is relatively small, and silicon carbide is hard, so the mold used for molding suffers from severe wear, making it difficult to form into precise shapes.

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 nonlinearity index α of 10 to 50, and the particle diameter can be made as small as about 10μ, so the voltage range is 10 to 1000V.
However, since the main component, zinc oxide, is chemically unstable, nonlinearity deteriorates over time, and the manufacturing process is labor-intensive and expensive. There is.

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 then sintered. This product has a higher nonlinear index α than silicon carbide-based varistors, selenium, and cuprous oxide-based varistors, and can achieve the desired C value without changing the α value.
It has the advantage of being able to realize values. However, this method had the disadvantage that it was difficult to uniformly disperse antimony oxide and bismuth oxide, which were 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 ),
A composition consisting of trace amounts of semiconducting elements and the remainder titanium oxide, with silicon dioxide added at 0.005% by weight or more.
It is characterized by containing less than 0.02% by weight (in terms of SiO ₂ ) and 0.005 to 3% by weight of calcium oxide (in terms of CaO).

In the present invention, powdered titanium oxide, bismuth oxide, and calcium oxide are usually used as the titanium oxide raw material, bismuth oxide raw material, and calcium oxide raw material, but titanium oxide, bismuth oxide, or calcium oxide can also be formed by firing. It is also possible to use substances that can. 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, for example, a titanium oxide raw material powder, a bismuth oxide raw material powder, a silicon dioxide raw material powder, and a calcium oxide raw material powder are mixed in a predetermined ratio into a powder mixture. A predetermined amount of a semiconducting element such as antimony oxide is added and thoroughly mixed using a wet ball mill or the like. Next, after drying this mixture, 800 ~
Calcinate at a temperature of 1000°C, and crush the calcined body. A suitable binder such as polyvinyl alcohol, CMC, etc. is added to the pulverized product, which is formed into granules, which is further press-molded into a suitable shape and sintered at a temperature of 1100 to 1400°C in air or an inert atmosphere. 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 ₅ ), 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.

In addition, silicon dioxide (SiO ₂ ) is 0.005% by weight.
If it is less than that, the particle size remains non-uniform, which is not preferred.

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. However, this is not preferable since it may actually cause deterioration of the electrical characteristics.

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 create low voltage devices without weakening their mechanical strength.
Further, since a material with uniform characteristics can be easily obtained, reliability such as voltage resistance can be significantly increased. Furthermore, since the α value can be significantly larger than that of silicon carbide-based varistors, it has the advantage of being applicable to a wide range of applications.In addition, it has the advantage of being able to reduce the price because it requires fewer types of raw materials. . 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 can be
Since the nonlinear index α can be increased at a voltage as low as 30V, it is suitable as a noise prevention element for micromotors.

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. Due to the presence of large self-inductance of the 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 Sh ₂ O ₃ 0.06 mol%, Bi ₂ O ₃ 0.5 mol% remaining TiO ₂
Silicon dioxide (SiO ₂ ) is added to a mixture of titanium oxide powder (average particle size 10μ or less) and bismuth oxide powder (average particle size 10μ or less) at a ratio of 0 to
0.020% by weight and calcium oxide in a range of 0.005 to 3% by weight were added 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 calcined material 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 some time it is made into granules.
It was press-molded into a disk shape with a diameter of 16 mm and a thickness of 1.2 mm.
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 previously proposed by the present inventors (Japanese Unexamined Patent Publication No. 55-115303), when the amount of silicon dioxide SiO ₂ added is less than 0.02% by weight, the varistor voltage increases rapidly, resulting in a product with a low varistor voltage. I couldn't help it. Therefore, lower the varistor voltage,
In order to increase the strength of the ceramic body, calcium oxide (CaO) was added to create a synergistic effect with silicon dioxide (SiO _{2 )} . In other words, as shown in Figure 1, by adding 0.005 to 3% by weight of CaO, it has become possible to reduce SiO ₂ to 0.02% by weight or less and approximately 0.005% by weight, thereby lowering the varistor voltage (3 to 10V). It is. As you can see from this table, the varistor voltage ranges from 0.005 to silicon dioxide.
It is extremely small in the range of 0.02% by weight and is suitable as a varistor for micro motors.

Next, when the thus obtained sintered body was observed under a microscope, it was found that the particle size of TiO ₂ in the sintered body without SiO ₂ was widely varied. On the other hand, the material to which 0.01% by weight of SiO ₂ is added has a more uniform particle size and has higher mechanical strength than the material without the addition of SiO ₂ .

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 Sh ₂ O ₃ 0.06mol%,
Bi ₂ O ₃ 0.5 mol % with 0.5 wt % CaO in the remaining TiO ₂
Added 0.01% by weight of _SiO2 ,
V ₁₀ (voltage when 10mA flows), 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 SiO ₂ . 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 SiO ₂ is added has excellent high-temperature continuous load characteristics.
FIG. 3 shows a pulse voltage application experiment, and FIG. 4 shows a measurement circuit diagram. The number of pulses is
This is done by changing the switch SW shown in Figure 4 10 times at a time, C is 0.1μF, and the applied voltage E is 250~
Measured in the range of 1250V. In FIG. 3, E shows the data of the same composition as in FIG. 2, and F shows the data without SiO ₂ added for comparison.

From FIG. 3, it can be seen that adding SiO ₂ 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, Fe ₂ O ₃ -based material B, SnO ₂ -based material C, ZnO-based material having a composition of mol%, titanium oxide 99.45 mol%, silicon oxide 0.01% by weight, and calcium oxide 0.5% by weight. Using D, electrodes were provided on both sides of a sintered body made of these materials to create a noise prevention element for a micromotor. Next, apply these noise prevention elements to the operating voltage.
Install between the coils of a 5V micro motor,
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, material A of the present invention exhibits superior properties compared to materials B, C, and D used for conventional noise cutting.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between SiO ₂ addition and varistor voltage according to the present invention. FIG. 2 shows high temperature continuous load characteristics, FIG. 3 shows a pulse application experiment, and FIG. 4 shows the experimental circuit of FIG. 3. 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 ),
0.005% by weight of silicon dioxide in a composition consisting of trace amounts of semiconducting elements and the remainder titanium oxide.
A voltage nonlinear resistance material characterized in that it contains less than 0.02% by weight (in terms of SiO ₂ ) and 0.005 to 3% by weight (in terms of CaO) of calcium oxide. 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: