JPH0582315A - Manufacture of nonlinear resistor - Google Patents

Abstract

PURPOSE:To enhance density and bending strength of a molded form by increasing plasticity of granulating powder, to improve nonlinear characteristic by suppressing generation of cracks, lamination, to shorten a molding step time by reducing a pressing pressure and to improve productivity. CONSTITUTION:In steps of manufacturing a nonlinear resistor, a mixture of polyvinyl alcohol and polyethylene glycol of 4:6-19:1 by weight is used as a binder. Its using amount is 0.5-3.0% to material powder. Further, the polyethylene glycol which has 50,000-300,000 of a molecular weight is employed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-linear resistor.

[0002]

2. Description of the Related Art Generally, a non-linear resistor does not follow Ohm's law and has a non-linear voltage-current characteristic that the resistance decreases and the current remarkably increases as the voltage increases.
It has a great effect in applications such as absorption of abnormal voltage such as lightning arresters and surge absorbers.

As a typical example of such a non-linear resistor, Si that applies the voltage sensitivity of the contact resistance of SiC particles is used.
There are C lightning arrester characteristic elements and SiC varistor, which are generally made by adding a porcelain binder composed of SiC particles and clay and then sintering at a high temperature after molding. And that voltage-
The current characteristic is approximately represented by I = (V / R) ^x . Here, I is current, V is voltage, R is a constant corresponding to the resistance value, and X is a nonlinear index.

The SiC lightning arrester characteristic element has an X value of 3 only in the current range of several hundred amps to 20 kiloamps.
It is about 7 to 7 and is close to the ohmic resistance outside this range. Therefore, the lightning arrester using the SiC characteristic element directly connected to the line needs a series gap to maintain the insulation between the line and the ground.

Further, a large number of gaps and characteristic elements are used in a high-voltage / ultra-high voltage lightning arrester. At this time, a capacitor or a resistor is required in parallel in order to equalize the voltage sharing of each gap.

As described above, mounting a large number of gaps, capacitors, and resistors not only increases the size of the insulator, which is a container, but also causes a gap to cause a bad response to a steep wave and a subsequent current interruption.

Therefore, zinc oxide is the main component, and oxides such as bismuth oxide, silicon dioxide, antimony oxide, cobalt oxide, manganese dioxide, chromium oxide, and nickel oxide are mixed as a secondary additive to form a disk shape or a column shape. Alternatively, after being formed into an appropriate shape and then sintered at a high temperature, both sides of this sintered semiconductor element body are covered with a side insulating material such as epoxy resin,
A non-linear resistor using an oxide semiconductor having electrodes on its upper and lower surfaces has been proposed.

The above-mentioned non-linear resistor has an X value of about 50 in the milliampere current region, and has a very excellent non-linearity and a considerably large dielectric constant as compared with the conventional SiC resistor.

Further, silicon dioxide is usually used as one component of the auxiliary additive, and when this is used, the characteristics of the non-linear resistor manufactured such as non-linearity, limiting voltage ratio, and stability of life are improved. It is known to improve.

Such a non-linear resistor is manufactured by the following method.

That is, after preliminarily pulverizing the above-mentioned auxiliary additives with a ball mill or the like, they are mixed with an organic binder and zinc oxide and dried with a spray dryer to obtain a raw material powder having good fluidity. Next, this raw material powder is molded into a shape such as a disk with a mold molding press, and after degreasing, 1000 ° C to 1300 ° C.
After firing for several hours, the insulating coating is applied to the side surfaces, both flat surfaces are polished, and aluminum electrodes are sprayed to complete the process.

Usually, polyvinyl alcohol (PV) having excellent adhesive strength is used as an organic binder in the above process.
A) is used, but the granulated powder produced using this is very hard and the particles are less likely to be crushed during molding, so the molding pressure of the granulated powder needs to be increased. In addition, the molding pressure,
Since there is a problem in the uniformity of the molding density and cracks and lamination easily occur, the moldability is improved by increasing the amount of PVA added so that the granulated powder is easily crushed.

[0013]

However, if the amount of PVA added is increased, the oxidation during firing becomes incomplete, carbonization occurs, and vacancies are likely to occur, so that the occurrence rate of internal pinholes increases. If the diameter of the pinhole is 1 mm or more or the number of pinholes is large, the resistor is destroyed by the insertion of switching surge or the like.

The present invention has been made on the basis of the above background, and increases the plasticity of the granulated powder to increase the density and bending strength of the molded product and suppresses the generation of cracks and lamination to achieve the non-linear characteristics. It is an object of the present invention to improve and further reduce the press pressure to shorten the molding process time and improve the productivity.

[0015]

In order to solve the above problems, the present invention is a slurry in which water and a binder are added to a raw material powder containing zinc oxide and a sub-additive component, and a dispersion peptizer is further added. In the method for producing a non-linear resistor having a step of producing a granulated powder by spray-drying this slurry, and a step of molding and firing this granulated powder, the weight ratio of the binder is A mixture of polyvinyl alcohol and polyethylene glycol (PEG) of 4: 6 to 19: 1 is used, and the amount thereof is 0.5 to the raw material powder.
It is characterized by being 3.0%.

The amount of the binder added is 0.5-2.0%, and polyethylene glycol has a molecular weight of 50,000-2.0.
There is also provided a method of manufacturing a non-linear resistor, which uses 300,000.

In the above-mentioned manufacturing method, it is preferable to use an anionic one such as polycarboxylic acid ammonium salt having a high dispersion peptizing ability as the dispersion peptizing agent.

PE which is added to PVA as a binder
When G has a molecular weight of less than 50,000, the strength of G decreases, and 3
If it exceeds 0,000, the density tends to be low and molding defects are likely to occur, so it is preferable to use one having a molecular weight of about 50,000 to 300,000.

The mixture of PVA and PEG can suppress the occurrence of molding failure by setting the weight ratio of the mixture to 4: 6 to 19: 1. A molded product having good bending strength can be obtained.

This is because when the PVA ratio is 19: 1 or more, the effect of adding PEG does not appear and the density of the molded product decreases, so that cracks and the like are likely to occur, and when the PVA addition amount is less than 4: 6, molding is performed. This is because the strength of the body decreases and lamination occurs.

Furthermore, when the amount of the binder, which is a mixture of PVA and PEG, added to the raw material powder is less than 0.5 wt%, the strength of the molded body becomes low and cracks and lamination occur during molding, and the amount added is 3.0%. If it exceeds the above range, the binder cannot be completely separated during firing, and carbonization causes voids or cracks to lower the discharge withstand capability. Therefore, the amount of the binder added is 0.5 to 3.0 wt%, preferably 0.5 to 2.0 wt%.

As described above, PVA and PEG are used as binders.
By using the mixture of (1), the plasticity of the granulated powder is increased and the density of the molded product is improved. Therefore, the press molding can be performed at a pressure lower than the conventional pressure.

[0023]

EXAMPLE In this example, a non-linear resistor was manufactured by using a mixed solution of polyvinyl alcohol (PVA) and polyethylene glycol (PEG) as a binder when manufacturing the non-linear resistor.

As shown in Table 1, in the conventional manufacturing method using only polyvinyl alcohol as the binder, when the amount of the binder added was about 2% of the raw material powder, pinhole defects and cracks were generated. The total number of defects can be kept low.

[0025]

[Table 1]

Therefore, first, in order to determine the mixing ratio of PVA and PEG, a non-linear resistor was manufactured as follows with the addition amount of the entire binder being 2%, and molding defects (pinholes and cracks) were produced. The incidence was investigated.

That is, the above-mentioned added raw material is preliminarily mixed and pulverized by a ball mill to form a slurry, and zinc oxide (ZnO) as a main component and an aqueous solution of an anionic dispersion peptizer are sufficiently mixed therein.

PVA and PEG as binders were added to this mixture.
A mixed aqueous solution in which and are mixed at various ratios is added and mixed by a ball mill to obtain a raw material slurry. Further, the raw material slurry is sufficiently defoamed and spray dried with a spray dryer to produce granulated powder.

The above-mentioned granulated powder is 80m in diameter by a dry molding press.
800 to 100 by molding in a disk shape (φ80-t30) with m and thickness of 30 mm
Calcination at 0 ℃ for 2 hours, apply insulating material to the side surface, and then 110
Baking is performed at 0 to 1250 ° C for 10 hours. Next, lead glass is applied to the side surface of the fired body, baked at 550 to 650 ° C., both planes are polished, and aluminum metallikon is performed to manufacture a non-linear resistor.

PV of the non-linear resistor manufactured by the above method
A graph of the defective molding occurrence rate with respect to the A ratio is shown in the graph of FIG. From this figure, the sum of PVA and PEG is 100%.
Then, it was found that when the PVA amount was in the range of 40 to 95%, no defective molding occurred and good characteristics were obtained.

This is because when PVA is more than 95%, PE
It is considered that the effect of the addition of G does not appear, the density of the molded product decreases, cracks and the like are likely to occur, and when the PVA is less than 40%, the strength of the molded product decreases and lamination occurs.

From the above results, PVA: PEG was 40: 6.
It can be seen that when the ratio is in the range of 0 to 95: 5 (19: 1), defects hardly occur and a good molded product can be obtained.

Next, in the above manufacturing method, PVA: P
Using a binder with EG of 4: 1, the addition amount to the raw material powder is 0.25, 0.5, 1.0, 2.0, 2.5, 3.0, respectively.
A non-linear resistor was produced at 4.0%, and the density of the molded body, the bending strength of the molded body, and the energy absorption capacity were measured for each amount of the binder added. The results are shown in FIGS. 2, 3, and 4, respectively.

FIG. 2 is a graph with the amount of binder added on the horizontal axis and the density of the compact on the vertical axis. The a1 line represents the resistor according to the present embodiment, and the b1 line represents the resistor according to the conventional manufacturing method. Show the characteristics. From this graph, it can be seen that the resistor according to this example has a higher density than that of the resistor according to the manufacturing method of the conventional example, and particularly the amount of the binder added is 0.5 to 3.0%.
In each of the ranges, a density higher than that of the conventional example was obtained.

Next, FIG. 3 is a graph in which the amount of binder added is plotted on the horizontal axis and the bending strength of the molded body is plotted on the vertical axis. The a2 line represents the resistor according to this embodiment and the b2 line represents the conventional manufacturing method. The characteristic of such a resistor is shown. From this graph, it is understood that the resistor according to the present example always has higher strength than the resistor according to the manufacturing method of the conventional example.

FIG. 4 is a graph in which the horizontal axis represents the amount of binder added and the vertical axis represents the energy absorption capacity. The a3 line is the resistor according to the present embodiment, and the b3 line is the resistance according to the conventional manufacturing method. Shows the characteristics of the body. From this graph, it can be seen that the resistor according to this example always has a higher absorption capacity than the resistor according to the manufacturing method of the conventional example. Therefore,
It can be seen from FIGS. 2 to 4 that good characteristics can be obtained by using a mixture of PVA and PEG as a binder.

Further, with respect to each of these resistors, occurrence rates of pinhole-type and crack-type defects with respect to the amount of the binder added were examined. The results are shown in Table 2.

[0038]

[Table 2]

According to this table, when the amount of the binder added is 0.5 to 2.5 wt% with respect to the raw material powder, neither pinhole type nor crack type defects occur, and the amount of the binder added is 0.5 to 3.0 wt%.
It can be seen that in the range of%, the defect occurrence rate is very low, and therefore good results are obtained.

This is because when the amount of the binder added is less than 0.5 wt%, the strength of the molded body becomes low and cracks and lamination occur during molding, and when the amount added exceeds 3.0%, the binder can be completely separated during firing. It is considered that this is because the carbonization causes voids or cracks and the discharge withstand capability decreases.

Furthermore, the correlation between the molecular weight of PEG and the incidence of defective molding was investigated. The result is shown in FIG. According to this figure, the strength decreases when the molecular weight of PEG is less than 50,000,
It can be seen that when it exceeds 300,000, the density is lowered and defective molding occurs. Therefore, the molecular weight of PEG is 50,000 to 3
It can be seen that it is better to use the one of about 100,000.

[0042]

INDUSTRIAL APPLICABILITY In the present invention, the plasticity of the granulated powder is increased and the density of the molded product is improved by adding the high thermal decomposable polymer PEG to PVA. Therefore, the bending strength is increased, and the occurrence of cracks and lamination is suppressed.

Therefore, the thickness of the molded body can be increased,
Larger size thick element can be manufactured, the assembly process when installing the resistor element in the lightning arrester is reduced, and the element body of the sintered body becomes dense, so the energy absorption capacity per unit volume is improved. To do.

Further, since the density of the molded body is remarkably higher than that of the conventional one, the press pressure until reaching the predetermined density can be lowered. Therefore, the pressurizing time, the depressurizing time, and the knockout time for discharging the molded product from the die can be greatly shortened, and the productivity of the molding process is greatly improved.

[Brief description of drawings]

FIG. 1 is a graph showing the correlation of the defect occurrence rate with the PEG addition ratio.

FIG. 2 is a graph showing a correlation between a binder addition amount and a compact density.

FIG. 3 is a graph showing the correlation between the amount of binder added and the bending strength of a molded body.

FIG. 4 is a graph showing the correlation between the amount of binder added and the energy absorption capacity.

FIG. 5 is a graph showing the correlation between the PEG molecular weight and the failure rate.

Claims (2)

[Claims] 1. A step of producing a slurry by adding water and a binder to a raw material powder containing zinc oxide and a secondary additive component, and further adding a dispersion peptizer, and spray-drying the slurry to obtain a granulated powder. A method for producing a non-linear resistor, which comprises a step of producing and molding and firing the granulated powder, wherein a mixture of polyvinyl alcohol and polyethylene glycol having a weight ratio of 4: 6 to 19: 1 as the binder is used. And the amount used is 0.5-3.0% of the raw material powder
And a method for manufacturing a non-linear resistor. 2. The non-linear resistor according to claim 1, wherein the amount of the binder added is 0.5 to 2.0% and the polyethylene glycol has a molecular weight of 50,000 to 300,000. Production method.