GB2286183A

GB2286183A - Process for preparation of raw material powder for ceramic capacitor

Info

Publication number: GB2286183A
Application number: GB9500940A
Authority: GB
Inventors: Syunsuke Nakaya; Shozo Kojima; Masami Yabuuchi
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 1994-01-21
Filing date: 1995-01-18
Publication date: 1995-08-09
Also published as: JPH07247169A; JP3784427B2; GB9500940D0; CN1112534A

Abstract

A process for preparation of a raw material powder for a ceramic capacitor by mixing main raw material and trace additives comprises grinding and mixing the trace additives, calcinating the ground trace additives, grinding and mixing the calcinated trace additives again and, thereafter, mixing them with main raw material. The main material may be BaTiO3 and the additives may comprise CaZrO3, MgTiO3, Al2O3 and SiO2.

Description

PROCESS FOR PREPARATION OF RAW MATERIAL POWDER FOR CERAMIC CAPACITOR The present invention relates to a process for preparation of a ceramic raw material powder. More particularly, it relates to a process for preparation of a ceramic raw material powder for ceramic capacitor.

A ceramic raw material powder for ceramic capacitor has been hitherto prepared by adding trace additives 22 such as CaZrO3, MgTiO3, A1203, SiO2 and the like to main raw material 21 such as BaTiO3 and the like and then mixing them using a ball mill as shown in Fig. 6.

In the above process, since particle size of main raw material and that of trace additives are different and trace additives are added therein at a small amount, main raw material and trace additives are difficult to be mixed uniformly in a shorter period of time.

When raw material and trace additives are mixed for a longer period of time in order to effect uniform mixing, the problems arise that contamination occurs and handling in later processes becomes difficult because of the excess increase in specific surface area of a raw material powder obtained by grinding.

In order to overcome the above problems, there has been provided a process for preparation of a raw material powder for ceramic capacitor by grinding and mixing trace additives and then adding main raw material thereto to mix as described in JP-A 4-170354. However, in this process, since respective particles of ground trace additives have the different composition, a partial segregation is liable to be caused in a step after main raw materials are added thereto to mix.

Accordingly, it would be desirable to be able to provide a process for preparation of a raw material powder for ceramic capacitor which can give a raw material powder having the higher extent of mixing of main raw material and trace additives and the uniform composition.

According to the present invention, there is provided a process for preparation of a raw material powder for ceramic capacitor by mixing main raw material and trace additives which comprises grinding and mixing the trace additives, calcinating the ground trace additives, grinding and mixing the calcinated trace additives again and, thereafter, mixing them with main raw material.

In the present process, trace additives are ground and mixed together and, thereby, trace additives are ground into a finely-divided powder (particle) and uniformly mixed. The ground and uniformly mixed trace additives are calcinated and, thereby, trace additives are thermally diffused to give a uniform compound.

Thereafter, the trace additives in the form of uniform compound are further ground and the ground trace additives are then mixed with main raw material and, thereby, trace additives and main raw material are well mixed.

Thus, in the present process, since trace additives are ground and mixed to calcinate, and the calcinated trace additives are further preferentially ground and the re-ground trace additives are mixed with main raw material, then the degree of mixing of main raw material and trace additives is increased and the composition of the raw material powder becomes uniform. Therefore, by using the raw material powder, the uniform solid solution can be obtained.

In addition, by filling, with trace additives, the voids formed by main raw material upon plastic treatment, the density of plastic solid can be increased.

Accordingly, by using the present raw material powder for ceramic capacitor, the capacitor having the high dielectric constant and the smaller dispersion of the dielectric constant and insulation resistance between the units can be manufactured.

By way of example only, the invention will now be described in more detail with reference to the accompanying drawings of which: Fig. 1 is a view schematically showing a raw material powder for ceramic capacitor prepared by one embodiment of the present process.

Fig. 2 is a view schematically showing one step of one embodiment of the present process.

Fig. 3 is a view schematically showing another step of one embodiment of the present process.

Fig. 4 is a view schematically showing a further step of one embodiment of the present process.

Fig. 5 is a view schematically showing plastic solid of a raw material powder for ceramic capacitor, prepared by one embodiment of the present process.

Fig. 6 is a view schematically showing a raw material powder prepared by the prior art.

Referring to Fig. 1, there is shown a raw material powder fPr ceramic capacitor prepared by the present process.

Upon preparation of the raw material powder for ceramic capacitor, trace additives 1 such as CaZrO3, MgTiOs, A1203, SiO2 and the like are first mixed to obtain a mixed powder la of trace additives as shown in Fig. 2.

Then the mixed powder la is ground to obtain a finely-divided powder lb as shown in Fig. 3.

Then the finely-divided powder lb of the trace additives is calcinated to obtain a uniform compound which is ground again to obtain a compound powder lc of the trace additives having the uniform composition as shown in Fig.

4.

Then the compound powder lc of the trace additives and main raw material 2 (BaTiO3 in this embodiment) are mixed to obtain a raw material powder 3 for ceramic capacitor having the uniform composition wherein the main raw material 2 and the compound powder lc of the trace additives are uniformly mixed. In the raw material powder 3 for ceramic capacitor thus prepared, the compound powder lc of the trace additives is adhered to the entire surface of the main raw material 2 (BaTiO3) as shown in Fig. 1.

Referring to Fig. 5, there is shown a plastic solid 4 formed by plastic treatment of the raw material powder 3 for ceramic capacitor. In this plastic solid 4, since the voids formed between the main raw material 2 (particle) are filed with the compound powder lc of the trace additives, the volume of voids is decreased and the density of the plastic solid 4 is increased.

In the raw material powder 3 for ceramic capacitor thus prepared, since the degree of mixing of the main raw material 2 and the compound powder 1c of the trace additives is increased and the composition of the raw material powder 3 for ceramic capacitor becomes uniform, the uniform solid solution can be prepared and the ferroelectric phase can be uniformly distributed in the unit.

Properties of stacked capacitor manufactured by using a raw material powder for ceramic capacitor prepared according to the present process and those of stacked capacitor manufactured by using a raw material powder for ceramic capacitor prepared according to the previous process are shown in Table 1 (1000 samples were tested, respectively). In Table 1, tested samples in accordance with two processes have the same values in composition, thickness of circuit element, surface area of electrode and number of layers except for process for preparation of them.

Table 1

Raw aw Material Present Previous Properties Process Process Capacitance Average 1155 950 (nF) MIU( 1180 1015 MIN 1123 896 a Lel 16.3 28.6 Insulation Av B.12xlOP 5.13x10e Resistance MA 8.71x109 7.76x109 (n) MIN 7.59x109 3.31x109 a 0.18xl09 0.92xr09 Dielectric Loss ($) 2.38 2.41 Rate of Capacitance -550C 2.9 2.6 Change to -300C 0.5 0.3 450C 1.1 1.3 mA-peratur 850C -3.2 -2.9 125 C 4.9 5.6 Rate of capacitance change was obtained using a value at 250C as a standard.

From Table 1, stacked ceramic capacitor in accordance with the present process has approximately the same dielectric loss and rate of capacitance change to temperature but has higher capacitance and insulation resistance and smaller deviation thereof in comparison with those in accordance with previous process.

Therefore, by using the raw material powder for ceramic capacitor prepared by the present process, the ceramic capacitor having the high dielectric constant and the smaller dispersion of the dielectric constant and insulation resistance between the units can be manufactured.

While the preferred embodiment of the present invention has been described, it is to be understood that a variety of modifications as to the composition of trace additives and main raw material will be apparent to those skilled in the art without departing from the spirit of the invention. In addition, the degree of mixing of the trace additives, the calcinating conditions, the degree of mixing after calcination and the like are not restricted to those of the foregoing disclosure and they can be appropriately selected depending upon the kind of trace additives and main raw material and the ratio thereof, as well as the properties required for ceramic capacitor.

Claims

1. A process for preparation of a raw material powder for ceramic capacitor by mixing main raw materials and trace additives which comprises grinding and mixing the trace additives, calcinating the ground trace additives, grinding and mixing the calcinated trace additives again and, thereafter, mixing them with main raw material.

2. The process according to claim 1, wherein the main raw material is BaTiO3.

3. The process according to claim 1 or 2, wherein the trace additives are selected from the group consisting of CaZrO3, MgTiO3, A1203 and SiO2.

4. A process for preparation of a raw material powder for a ceramic capacitor substantially as described herein with reference to Figs 1 to 5 of the accompanying drawings.