JPS637002B2 - - 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, aluminum 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 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 100μ in clay, and this 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 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 in terms of corrosion of manufacturing equipment and pollution problems, and the countermeasures for these problems have included drawbacks such as relatively high manufacturing costs.

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 10V 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 aluminum oxide is added in an amount of 0.005 to 3% by weight (in terms of Al ₂ O ₃ ) to a composition consisting of a trace amount of a semiconducting 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, powdered titanium oxide, bismuth oxide, aluminum oxide, and calcium oxide are usually used as the titanium oxide raw material, bismuth oxide raw material, aluminum oxide raw material, and calcium oxide raw material. Substances capable of forming bismuth, aluminum 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, an aluminum oxide raw powder, and, if necessary, a calcium oxide raw powder at 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, further press-molded into an appropriate shape, and heated to a temperature of 1100 to
Sintering at a temperature of 1400℃. 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-forming element is preferably at least one of antimony oxide (Sb ₂ O ₃ ), niobium oxide (Nb ₂ O ₅ ), and tantalum oxide (Ta ₂ O ₅ ), and it is preferable that the content thereof is less than 0.002 mol%. Nonlinearity cannot be obtained. In addition, when this exceeds 0.074 mol%, no improvement in nonlinearity is observed, and
Nonlinearity in 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, aluminum oxide (Al ₂ O ₃ ) 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. However, this is not preferable since it may actually cause deterioration of the electrical characteristics. The present invention lowers the varistor voltage by 2 to 3 V by adding calcium oxide (CaO) at 0.02% by weight or less of aluminum oxide (Al ₂ O ₃ ).
Furthermore, the aim is to obtain a synergistic effect of increasing the strength of the ceramic body in this region and thereby making it possible to downsize the varistor element.

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 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 able to reduce the price because 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 can be
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 appears 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 10μ or less), add 0.005 to 0.05% of aluminum oxide (Al ₂ O ₃ )
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 0.005 to aluminum oxide.
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 aluminum oxide added, making it suitable as a varistor for micromotors. In addition, if Al ₂ O ₃ is 3% by weight or more, the change in varistor voltage (V/mm) becomes large, so a slight difference in Al ₂ O ₃ will cause a large fluctuation in the varistor voltage, which will reduce the yield of the product, so it is not preferable. do not have.

When the sintered body thus obtained is observed under a microscope,
In the case where Al ₂ O ₃ is not added, the particle size of TiO ₂ varies widely. On the other hand, when Al ₂ O ₃ is added in an amount of 0.005% by weight or more, the particle size is more uniform and the mechanical strength is stronger than when Al ₂ O ₃ is not added. 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 Al ₂ O ₃ 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 Al ₂ O ₃ 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 Al ₂ O ₃ . 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. It can be seen that the material to which Al ₂ O ₃ is added has excellent high-temperature continuous load characteristics. Figure 3 shows the pulse voltage application experiment;
The measurement circuit diagram is shown in the figure. 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 applied voltage E is 250 μF.
Measured in the range ~1250V. In Figure 3, Ho is the second
The data is based on the same composition as in the figure, and F is the data without Al ₂ O ₃ added for comparison.

From FIG. 3, it can be seen that adding Al ₂ O ₃ 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 with a composition of mol%, titanium oxide 99.45 mol% and aluminum oxide 0.5% by weight
Using system material 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, 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, 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 Al ₂ O ₃ 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 ),
For a composition consisting of trace amounts of semiconducting elements and the remainder titanium oxide, aluminum oxide is added in an amount of 0.005~
A voltage nonlinear resistance material characterized by containing 3% by weight (calculated as Al ₂ O ₃ ). 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 ),
For a composition consisting of trace amounts of semiconducting elements and the remainder titanium oxide, aluminum oxide is added in an amount of 0.005~
3% by weight (calculated as Al ₂ O ₃ ) and calcium oxide 0.005~
Voltage nonlinear resistance material containing 3% by weight (calculated as CaO).