JPH07153646A - Manufacture of laminated porcelain capacitor - Google Patents

Abstract

PURPOSE:To obtain uniform ceramic slurry without excessively grinding ceramic powder in the formation of ceramic slurry used for manufacturing a laminated porcelain capacitor. CONSTITUTION:Ceramic powder and organic binder are mixed together and dispersed by a ball mill in a first process and then mixed together and dispersed by a sand mill in a second process. Therefore, uniformly dispersed ceramic slurry can be obtained through a ball mill and a sand mill without excessively grinding ceramic powder. A thin ceramic green sheet capable of coping enough with a dielectric layer lessened in thickness and very uniform in quality can be formed preventing defects such as inner voids or the like from occurring. By this setup, a laminated porcelain capacitor excellent in characteristics such as electrostatic capacity temperature characteristics, small in size, and large in capacity can be easily and efficiently manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a laminated ceramic capacitor, and more particularly, to an improved method of mixing and dispersing ceramic slurry when forming a ceramic green sheet, which is one step of manufacturing a laminated ceramic capacitor. The present invention relates to a method for manufacturing a laminated ceramic capacitor.

[0002]

2. Description of the Related Art Conventionally, a laminated ceramic capacitor is generally manufactured as follows. That is, first, a ceramic dielectric powder and an organic binder component are mixed and dispersed by a ball mill or the like to prepare a ceramic slurry, and this ceramic slurry is molded by a doctor blade method, a reverse coater method or the like to prepare a ceramic green sheet. . Next, a metal electrode paste is applied as an internal electrode to this ceramic green sheet by printing or the like, a plurality of ceramic green sheets are laminated and pressure-bonded so that the internal electrodes are alternately exposed, and then cut into chips.
Then, the binder is removed and fired to produce a laminated ceramic capacitor bare chip. External electrodes are formed on both end surfaces of this bare chip to manufacture a laminated ceramic capacitor.

[0003]

In recent years, multilayer ceramic capacitors have tended to become smaller and larger in capacity, and the thickness of the internal dielectric layer has been reduced from 50 to 20 μm to 10 μm or less. It's starting. As the thickness of the ceramic green sheet is reduced, it is required that the ceramic green sheet be made extremely uniform. That is, if the ceramic green sheet is not substantially homogeneous, defects such as voids (holes) are likely to occur in the thin ceramic green sheet. This leads to a defect in electrical characteristics such as a decrease in resistance value and a deterioration in withstand voltage value.

On the other hand, if the mixing and dispersion of the ceramic slurry by a ball mill or the like is promoted, that is, the rotation time or the number of rotations is increased, in order to enhance the dispersion state of the ceramic slurry in order to produce a homogeneous ceramic green sheet. This causes excessive pulverization of the ceramic powder, which results in a problem that the transformation of the crystal structure causes deterioration of the temperature characteristic of the capacitance of the obtained laminated ceramic capacitor.

For example, X7R characteristics (-55 to -125 ° C) containing barium titanate as a main component as a ceramic powder.
For a laminated porcelain capacitor whose capacitance change rate is within ± 15% in the temperature range of 1), by forming a core cell structure, the obtained laminated porcelain capacitor has a high dielectric constant and stable temperature characteristic of capacitance. However, in this case, if the ceramic powder is excessively pulverized, the core cell structure cannot be formed, and it becomes difficult to obtain stable capacitance-temperature characteristics.

The present invention solves the above-mentioned conventional problems, and in the preparation of a ceramic slurry in the production of a laminated ceramic capacitor, the ceramic powder is efficiently mixed and dispersed without being excessively pulverized to obtain a uniform ceramic. An object of the present invention is to provide a method for manufacturing a laminated ceramic capacitor that can obtain a rally.

[0007]

According to a first aspect of the present invention, there is provided a method for manufacturing a laminated ceramic capacitor, which comprises a step of preparing a ceramic slurry by mixing and dispersing ceramic powder and an organic binder, and molding the ceramic slurry to form a ceramic. In the method for manufacturing a laminated ceramic capacitor including a step of obtaining a green sheet, the ceramic slurry preparation step,
It is characterized by including a primary mixing and dispersing step by a ball mill and a secondary mixing and dispersing step by a sand mill.

According to a second aspect of the present invention, there is provided a method of manufacturing a laminated ceramic capacitor according to the first aspect, wherein the ceramic slurry preparing step includes a primary mixing and dispersing step by a ball mill and a secondary mixing and dispersing step by a sand mill. And a third mixing and dispersing step by means of ultrasonic dispersing means.

The present invention will be described in detail below.

In the method for manufacturing a laminated ceramic capacitor of the present invention, when a ceramic slurry is prepared by mixing and dispersing a ceramic powder and an organic binder, the mixing and dispersion are carried out by a primary mixing and dispersion process using a ball mill, and a sand mill. The second mixing and dispersing step according to the above step and, if necessary, the third mixing and dispersing step by the ultrasonic dispersing means.

In the ball mill used in the first mixing and dispersing step in the present invention, boulders and ceramic powder as a media and an organic binder are put into a cylindrical container,
The structure is such that the container is hermetically closed and the container is rotated to perform mixing and dispersion, which has been conventionally used.

In the normal case, L (length) / D (diameter) =
A ball mill made of nylon, alumina, porcelain, etc. with a ratio of 2.0 to 1.0, especially L / D≈1.4, and stabilized zircon core, titania, natural stone (silica), alumina as media material. For example, spherical or columnar boulders are used. The size of the cobblestone is 5 to 25 mm
It is the diameter, and the amount of boulders is preferably 40 to 60% of the internal volume of the ball mill. The ball mill processing conditions are set by appropriately combining the above requirements. The rotation speed varies depending on the shape of the ball mill, but it is 10 to 100 rpm, and it is usually used for a rotation time of about 5 to 50 hours.

Due to the above-mentioned constitution, the media is relatively large in the mixing and dispersion method by the ball mill.
There is a limit to the mixing and dispersion of the recent ceramic powder which has become ultrafine powder, and there is a problem that if it is treated for a long period of time, the powder becomes too fine.

In the present invention, after such a primary mixing and dispersing step using a ball mill, a secondary mixing and dispersing step using a sand mill (also referred to as a bead mill) and, if necessary, an ultrasonic dispersing means. Since the third mixing and dispersing process is performed, the processing conditions of the first mixing and dispersing process by the ball mill can be relaxed as compared with the conventional method of only mixing and dispersing by the ball mill. It takes about 1 to 10 hours.

The sand mill used in the secondary mixing and dispersing step has a small diameter (0.5-5.
It has a structure in which a spherical one having a diameter of about 0 mm) is charged in an amount of 30 to 95% of the internal volume, and a rotation mechanism for stirring the media is further provided inside the container.

According to the present invention, the ceramic powder slurry that has undergone the primary mixing and dispersing steps by a ball mill is passed through such a sand mill to mix and disperse. Since the slurry is passed through, the ultrafine powder can be mixed and dispersed relatively efficiently.

The volume of the cylindrical container of the sand mill is 0.5 to
About 250 liters, the material is stabilized zirconia,
Alumina and rubber are preferable, and stabilized media such as stabilized zirconium, alumina and glass beads can be used. The usage conditions of the sand mill are 300 to 300 rpm.
3000 rpm, slurry supply amount 0.5-2000 ml
The treatment is preferably performed once / minute for 1 to several times.

As the ultrasonic dispersing means used in the third mixing and dispersing step, the ceramic slurry is uniformly used in an amount of 16 to 2
Any structure that gives an ultrasonic oscillating wave of about 00 kHz may be used, and in particular, a structure in which a certain amount of slurry is sent through the ultrasonic chamber is preferable in terms of ensuring the dispersion effect.

As the ultrasonic disperser, a slurry pumping unit,
An ultrasonic oscillating unit, an ultrasonic processing unit, and a take-out / collecting unit are provided, and an ultrasonic oscillating and processing unit is provided with a cooling mechanism.
It is preferably 0 to 2000 ml / min.

By mixing and dispersing the ceramic slurry using an ultrasonic dispersing means, it is possible to further promote the bonding and wetting property of the ceramic powder and the organic binder, and when performing degassing under reduced pressure after the treatment. However, foaming does not occur at all.

In the method of the present invention, the mixing and dispersing in the preparation of the ceramic slurry are carried out in the primary mixing, dispersing step and the secondary mixing, dispersing step, or the third mixing and dispersing step as described above. Other than the above, it can be implemented in the same manner as the conventional one.

That is, a predetermined ratio of the ceramic dielectric powder and the organic binder component are mixed and dispersed by the above-mentioned method, and the obtained ceramic slurry is molded by a doctor blade method, a reverse coater method or the like to obtain a ceramic green sheet. . Next, an internal electrode is formed on the ceramic green sheet with a metal electrode paste, and a plurality of sheets are laminated and pressure-bonded, and then cut into a predetermined size.
Next, a binder removal treatment is performed, and firing is performed at 1200 to 1350 ° C. for about 0.5 to 3.0 hours to obtain a laminated ceramic capacitor bare chip, and metal electrode paste is applied to both end surfaces of the bare chip and baked to form an external electrode. To obtain a laminated ceramic capacitor.

[0023]

In preparing the ceramic slurry, it is possible to obtain a ceramic slurry in a uniformly dispersed state without over-pulverizing the ceramic powder by mixing and dispersing with a ball mill and mixing and dispersing with a sand mill. It

Furthermore, by adding mixing and dispersion by means of ultrasonic dispersion means, a more excellent uniform dispersion state can be achieved.

[0025]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below. For convenience of description, a comparative example will be given first.

Comparative Example 1 600 g of a dielectric composition having the following composition was weighed and put into a nylon ball mill (L / D = 1.4), and stabilized zirconium boulders (particle size = 10 mm) were used as a mediar in the ball mill internal volume. 1/2 of the amount of
VB (polyvinyl butyral) resin 10% by weight solution (solvent: toluene / ethanol = 60/40 (weight ratio)) 4
20 g, dioctyl phthalate (DOP) as a plasticizer
28g each, ball mill rotation time, 2
Ceramic slurries were prepared for 4, 48 and 72 hours. The rotation speed of the ball mill was 70 rpm.

Dielectric composition (wt%) Barium titanate (BaTiO ₃ ): 98.15 Niobium pentoxide (VO ₅ ): 1.20 Zinc oxide (ZnO): 0.60 Cobalt trioxide (Co _3). O ₄ ): 0.05 Using each of the ceramic slurries, a green sheet having a thickness of 25 μm was prepared by a green sheet molding machine (doctor blade system). Palladium electrode paste is printed on this green sheet to form internal electrodes, and 11 sheets of this internal electroprinting sheet and 7 sheets without electrodes on top and bottom, 25 sheets in total, are stacked and heated and pressure-bonded at 60 ° C. and 300 kg / cm ^2. After that, cut and 2.0 x 1.25 mm x 0.6 mm
The thickness of the chips is 1280 ° C. in a baking furnace.
It was baked by holding for 2 hours. Then, silver electrode paste was applied to both end faces and baked to form external electrodes.

The capacitance, tan δ, capacitance-temperature characteristic (TCC) and void diameter inside the device were measured for each of the samples thus obtained, and the results are summarized in Table 1.

[0029]

[Table 1]

From Table 1, it is seen that as the ball mill rotation time increases, the internal void diameter tends to decrease, but on the other hand, T
The CC greatly increases from -5.3% to -21.0%, and it is clear that the ball mill treatment alone does not provide a satisfactory value for any performance.

Example 1 In Comparative Example 1, in preparing the ceramic slurry,
Samples were prepared in the same manner except that the mixing and dispersion were performed by a ball mill and a sand mill, or further by an ultrasonic homogenizer, and the same evaluation was performed. The results are shown in Table 2.

A ball mill similar to that used in Comparative Example 1 was used, and the rotation speed was 70 rpm. The rotation time is as shown in Table 2. A stabilized zirconia container and a media were used as the sand mill. The container had a cylindrical shape with an internal volume of 1 liter, and the medium used was a spherical one having a diameter of 2.0 mm and 800 cc. Slurry feed rate is 400 ml / min, rotation speed is 1600 rpm
And treated twice (2P).

An ultrasonic disperser ("GSD-600" manufactured by SMT Co., Ltd.) has a frequency of 50 kHz and an output of 300.
W was used, the treatment amount was 1 liter / min, and this was also treated twice (2P).

[0034]

[Table 2]

As is clear from Table 2, in the preparation of the ceramic slurry, the mixing and dispersion were performed by the ball mill first.
By performing the secondary mixing and dispersing steps and the secondary mixing and dispersing steps by the sand mill, the capacitance temperature characteristic and the internal void can be satisfied at the same time. In addition,
By adding ultrasonic dispersion means, the internal voids can be further reduced.

[0036]

As described above in detail, according to the method for manufacturing a laminated ceramic capacitor of the present invention, a ceramic slurry in a uniformly dispersed state can be prepared without over-pulverizing the ceramic powder, so that the laminated ceramic capacitor The thin-layer ceramic green sheet that can sufficiently cope with the thinning of the dielectric layer can be produced as an extremely homogeneous sheet while suppressing the occurrence of defects such as internal voids. Therefore, according to the present invention, it is possible to easily and efficiently create a method for manufacturing a small-sized, large-capacity laminated ceramic capacitor which is excellent in various characteristics such as capacitance temperature characteristics.

According to the method of manufacturing a laminated ceramic capacitor of the second aspect, defects such as internal voids can be more surely reduced.

Claims (2)

[Claims] 1. A step of mixing and dispersing ceramic powder and an organic binder to prepare a ceramic slurry,
In a method of manufacturing a laminated ceramic capacitor, including a step of molding the ceramic slurry to obtain a ceramic green sheet, the ceramic slurry preparing step includes a primary mixing and dispersing step by a ball mill and a secondary mixing and dispersing step by a sand mill. A method of manufacturing a laminated ceramic capacitor, comprising: 2. The method according to claim 1, wherein the ceramic slurry preparing step is a primary mixing by a ball mill,
A method of manufacturing a laminated ceramic capacitor, comprising: a dispersion step, a secondary mixing and dispersion step by a sand mill, and a third mixing and dispersion step by an ultrasonic dispersion means.