JP2003264103A - Manufacturing method of varistor and varistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve productivity and manufacture a high quality varistor having high surge resistance. <P>SOLUTION: A ceramic mold is made by filling a cavity 11 with the slurry material not containing binder, then closing the cavity 11 with a pressure receiver 9 having a filter 10 secured beneath, and moving a pusher 6 in the arrow direction P to press the slurry material up to predetermined pressure to dehydrate the slurry material draining water in the slurry through small holes 8... then, a varistor is obtained by making a ceramic element 2 by sintering the ceramic mold and covering it with a resin such as epoxy resin after forming electrodes. <P>COPYRIGHT: (C)2003,JPO

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 varistor and a varistor manufactured by using the manufacturing method.

[0002]

2. Description of the Related Art With the recent high integration of various electronic device circuits, varistors are widely used as electronic components for protection against lightning surges and abnormal voltages.

As a method of manufacturing this type of varistor, a predetermined ceramic raw material is wet-mixed, dehydrated, and then a binder such as polyvinyl alcohol is added at about 5 wt% to granulate, and the granulation is performed. There is known a technique in which a material is press-molded by a dry pressure press to form a molded body, and the molded body is fired to obtain a varistor (for example, JP-A-5-74606 and JP-A-5-60660). -2347
No. 16, JP-A-6-314603).

[0004]

However, in the above-mentioned conventional technique, since the molded body contains the binder, the molded body has a low density. Therefore, in order to obtain a good ceramic sintered body, degreasing treatment is performed for a long time to thermally decompose the binder, and then firing treatment is performed.

Therefore, when the above-mentioned degreasing treatment is insufficient or when the temperature is rapidly raised, sintering becomes insufficient and a varistor having desired characteristics cannot be obtained. That is, in the past, it took a long time to manufacture a varistor,
Especially when obtaining a large number of varistor elements from a large-sized ceramic body, a long firing time including degreasing treatment is required,
There was a problem of poor productivity.

If binder agglomeration or segregation is present in the granulated product, defects such as pores are liable to occur in the ceramic body, which leads to a decrease in surge withstand and stability of quality. There was a problem that it might be damaged.

The present invention has been made in view of the above problems, and a method of manufacturing a varistor capable of manufacturing a high quality varistor having excellent surge resistance while improving productivity, and the manufacturing method. It is intended to provide a varistor manufactured using the method.

[0008]

In order to achieve the above object, a method of manufacturing a varistor according to the present invention is to prepare a slurry-like forming raw material in which water is added to a ceramic powder and a binder is not contained, and the forming is performed. The method is characterized in that after the raw material is poured into the mold, water is dehydrated and removed while pressurizing the molding raw material to produce a molded body, and then the molded body is subjected to a firing treatment to produce a varistor.

According to the above-mentioned manufacturing method, since the molded body is manufactured by the dehydration molding method without containing the binder in the slurry, the degreasing treatment for a long time becomes unnecessary, and the productivity can be improved. .

Further, since the binder is not included, the density of the compact can be increased, and since agglomeration and segregation due to the binder do not occur, a ceramic sintered body having no defect can be obtained. Therefore, it becomes possible to manufacture a varistor having desired characteristics.

Further, since the varistor according to the present invention is manufactured by the above manufacturing method, a binder component is not contained in the varistor and a varistor having a high surge resistance and high quality can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an external view of a varistor manufactured by the manufacturing method of the present invention, and FIG. 2 is a sectional view taken along line AA of FIG.

In FIGS. 1 and 2, reference numeral 1 is a varistor, and the varistor 1 is an upper surface of a disk-shaped ceramic body 2 containing zinc oxide (ZnO) or strontium titanate (SrTiO ₃ ) as a main component and Electrodes 3a and 3b made of a conductive material such as Ag are formed in a circular shape on the lower surface, and lead terminals 4a and 4b are connected to the electrodes 3a and 3b, respectively, and the ceramic body 2 is made of epoxy resin or the like. It is covered with a resin material 5.

Next, the method of manufacturing the varistor will be described in detail.

First, a predetermined ceramic raw material containing ZnO or SrTiO ₃ as a main component is wet mixed in a pot mill, dehydrated and dried to prepare a raw material powder, and then a predetermined amount of water, a dispersant, and the like are added to the raw material powder. Then, the defoaming agent is put into a pot mill and mixed for a predetermined time to make the raw material powder into a slurry, and the slurry-like raw material (forming raw material) is subjected to a dehydration forming treatment.

FIG. 3 is a cross-sectional view of the main parts of the dehydration molding apparatus. In the dehydration molding apparatus, a pressing portion 6 having a T-shaped cross section for pressing in the direction of arrow P is fitted into a substantially cylindrical mold frame portion 7. In addition, the pressure receiving portion 9 is a filter 1 formed of filter paper, filter cloth, or the like.
The filter 10 is disposed so as to face the pressing portion 6 via 0, and the outer peripheral end portion of the filter 10 is in contact with the inner peripheral upper end portion of the mold frame portion 7. That is, the cavity portion 11 into which the slurry-like raw material is poured is surrounded by the pressing portion 6, the mold frame portion 7 and the filter 10. Further, the pressure receiving portion 9 has an appropriate number of small holes 8 ...
Is provided so that the water contained in the slurry-like raw material can be removed by dehydration.

Then, after pouring the slurry-like raw material into the cavity 11 from above in the figure, the cavity 11 is closed by the pressure receiving portion 9 to which the filter 10 is fixed at the lower end, and the outer peripheral end of the filter 10 and the formwork. The upper end of the inner periphery of the portion 7 is brought into contact with the portion 7 to seal the slurry-like raw material so as not to leak outside. Then, the pressing portion 6 is moved in the direction of arrow P to apply a predetermined pressure to the slurry-like raw material, whereby the water contained in the slurry-like raw material is discharged to the outside through the small holes 8 ... The raw material is subjected to dehydration treatment to produce a disk-shaped ceramic molded body.

After that, the ceramic molded body is put in an alumina pod and subjected to a firing treatment, whereby the ceramic body 2 is manufactured.

Next, a conductive paste containing silver (Ag) as a main component is applied on both upper and lower surfaces of the ceramic body 2.
The electrodes 3a, 3b are formed by baking, and the electrodes 3a, 3b are formed.
The lead wires 4a and 4b are soldered to and the ceramic body 2 is covered with a resin material 5 such as an epoxy resin, whereby a varistor is manufactured.

Since the varistor thus manufactured does not contain a binder in the ceramic molded body which is an intermediate product, it does not require a long-time degreasing treatment as in the conventional case, and the firing time is greatly shortened. Therefore, the productivity can be improved.

In addition, since the varistor does not contain a binder in the ceramic molded body, defects such as pores due to agglomeration and segregation of the binder do not occur as in the conventional case, and the surge resistance is high. It is possible to obtain a stable and high quality varistor.

The present invention is not limited to the above embodiment, and for example, a large-sized ceramic molded body 12 capable of obtaining a large number of varistors as shown in FIG. 4 is manufactured by the above-described dehydration molding treatment. Alternatively, a desired rectangular varistor may be obtained by cutting it with a dicing saw or the like into a predetermined size as shown by a broken line. In particular, when a rectangular varistor is obtained from a large-sized ceramic molded body 12 in the related art, since the large-sized ceramic molded body 12 contains a binder, a long-time degreasing process is required, and the productivity is improved. Although it is a hindrance to the above, in the present invention, since the ceramic raw material is produced by the dehydration molding process without including the binder in the slurry-like raw material, a large number of square varistors can be shortened from the large-sized ceramic molded body. It can be easily manufactured in time, and productivity can be improved.

[0024]

EXAMPLES Next, examples of the present invention will be specifically described.

The present inventors have found that ZnO: 97.5 mol%, B
i_TwoO_Three: 0.5 mol%, Co_ThreeO _Four: 1.0 mol%,
Mn_ThreeO_Four: Weigh 1.0 mol% and put it in the pot mill
Then wet-mix and pulverize, dehydrate and dry to give ZnO
A ceramic raw material powder containing as a main component was produced.

Next, with respect to the above ceramic raw material, water:
50.0 wt%, polyoxyalkylene glycol as a dispersant: 2.0 wt%, and polyether-based defoaming agent: 0.5 wt% were put into the above pot mill, and wet 2
It was pulverized for 0 hours to prepare a slurry-form raw material (forming raw material).

Next, the slurry-like raw material was put into a dehydration molding apparatus (see FIG. 3) and subjected to dehydration molding treatment. That is, after pouring the above slurry-like raw material into the cavity portion 11, the pressure receiving portion 9 is closed and the pressing portion 6 is moved in the direction of arrow P, so that 9.8 × 10 ⁶ Pa (1
A pressure of 00 kgf / cm ² ) was applied for 5 minutes to discharge the water contained in the slurry-like raw material from the filter 10 into the small holes 8 ..., thereby producing a ceramic molded body having a diameter of 10 mm and a thickness of 2 mm.

Next, the ceramic molded body thus produced was taken out from the dehydration molding apparatus, put into an alumina jar, and kept at a temperature rising rate of 10 ° C./min for 2 hours at a temperature of 400 ° C. After degreasing treatment, the temperature is 1000
It was kept at 2 ° C. for 2 hours and fired to produce a ceramic body.

Next, on the upper and lower surfaces of the ceramic body,
An Ag paste was applied and baked to form an Ag electrode, a lead wire was soldered to the Ag electrode, and coated with an epoxy resin to prepare an example test piece.

The inventor of the present invention also prepared a comparative test piece as follows.

That is, in the same manner as described above, a ceramic raw material powder containing ZnO as a main component was prepared, and then 5 wt% of polyvinyl alcohol was added as a binder to granulate the mixture, and the mixture was granulated with a dry pressure press at 9.8 × 10 ⁶ Pa. Pressing is carried out by applying pressure for 5 minutes, and the diameter is 10 m as described above.
A ceramic molded body having a thickness of m and a thickness of 2 mm was produced.

Since the ceramic molded body contains a binder (polyvinyl alcohol),
As in the conventional case, sufficient degreasing treatment was performed for 5 hours, and thereafter, as in the above case, the temperature was maintained at 1000 ° C. for 2 hours to perform firing treatment, and a ceramic element body was produced.

Then, after forming electrodes as described above,
The lead wire was soldered and the ceramic body was covered with an epoxy resin to prepare a comparative test piece.

The inventors of the present invention applied a lightning current waveform of 8/20 μsec to the test pieces of the example and the comparative example four times continuously at 5 minute intervals, and changed 10% from the initial value when voltage was applied. The current at that time was measured as surge withstand, and the current was measured.

As a result, the comparative test piece was 1.75 × 10.
^{It was 5} A / m ² , whereas the example test piece was 2.30.
It was confirmed that the surge resistance was improved to × 10 ⁵ A / m ² .

[0036]

As described in detail above, in the method for manufacturing a varistor according to the present invention, a slurry-like forming raw material is prepared by adding water to a ceramic material and containing no binder, and the forming raw material is used inside a mold. After that, the water content is dehydrated and removed while pressurizing the forming raw material to produce a formed body, and then the formed body is subjected to a firing treatment to produce a varistor, so that the slurry contains a binder. However, this eliminates the need for a long-time degreasing treatment and improves productivity.

Further, the density of the molded body can be increased,
Further, since the binder does not agglomerate or segregate, a varistor having an improved surge resistance can be manufactured without causing defects in the sintered body.

Further, since the varistor according to the present invention is manufactured by the above-mentioned manufacturing method, the varistor does not contain a binder component and a surge resistance is high and a high quality varistor can be obtained.

[Brief description of drawings]

FIG. 1 is an outline view showing an embodiment of a varistor manufactured by a manufacturing method of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a cross-sectional view of essential parts of a dehydration molding processing apparatus used in the method of manufacturing a varistor according to the present invention.

FIG. 4 is a perspective view of a large-sized ceramic molded body for explaining another embodiment of the present invention.

[Explanation of symbols]

8 small holes 10 filters 11 Cavity (inside the mold)

Claims (2)

[Claims] 1. A ceramic raw material is prepared by adding water to a ceramic material and containing no binder, casting the raw material into a mold, and then dehydrating and removing water while pressurizing the raw material. The method for producing a varistor is characterized in that a varistor is produced by producing a molded article by performing a firing treatment on the molded article. 2. A varistor manufactured by the manufacturing method according to claim 1.