JP3018683B2 - Method for producing lead-containing ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing lead-containing ceramics, and more particularly to a method for firing lead-containing ceramics such as PZT (lead zirconate titanate) and PT (lead titanate) ceramics. Controlling the atmosphere of lead during firing in order to reduce the warpage that occurs, facilitate the scattering of the binder, reduce the cracking defect, and suppress the evaporation of PbO, which is likely to occur in lead-based ceramics, and the variation in the characteristics of fired ceramics The present invention relates to a method for producing a ceramic containing lead.

[0002]

2. Description of the Related Art Generally, when a plate-shaped ceramic compact is fired, the sintered compact is warped. In order to reduce this, a ceramic plate having the same composition as the ceramic molded body is arranged on one or both sides of the stacked ceramic molded body, or both. The ceramic plate is called a setter, and the setter minimizes the warpage by wrapping and the like, and the surface accuracy reduces the warpage of the ceramic molded body during firing. The mechanism of this warpage reduction is as follows. The weight of the setter arranged on the upper side suppresses the ceramics, and the warpage is reduced. The ceramics of the setter arranged on the lower side are softened at a high temperature at the time of firing and deformed along the surface of the setter by the weight of the formed body, so that the warpage unique to the formed body is eliminated. As a countermeasure against the variation in the characteristics of ceramics due to the atmosphere of PbO, PbO is sealed in a sealed container of platinum, magnesia, alumina or the like.
The baking is performed so that the atmosphere is not scattered.

[0003]

According to the above prior art, the evaporation of lead in ceramics can be suppressed for the time being, but when a plurality of ceramic plates are stacked and fired, the characteristic variation between the number of stacking stages is reduced. This occurred and the variation among firing lots was large. That is, the atmosphere of heavy PbO gathered at the bottom of the firing container, and the lower the stacking stage, the lower the firing temperature of the ceramics, and the higher the firing temperature, the more the characteristics of the ceramics fluctuated. Further, in particular, in the case of ceramics having a composition in which lead easily evaporates, there is a problem in that even when fired in a closed container, lead evaporates and characteristics are deteriorated. In such a case, firing is performed by placing a PbO powder or the like that releases a lead atmosphere in a firing box. In this case as well, characteristic variations due to the concentration gradient in the height direction of the above-mentioned lead atmosphere occur, which has been a problem. The above problems are particularly important for piezoelectric ceramics such as a ceramic filter or a ceramic oscillator in which a variation in sound speed of 0.5% or less becomes a problem. In addition, in the conventional method, since the upper and lower sides of the molded body containing the binder are sandwiched between ceramic plates,
There has been a problem that the binder is not easily scattered, and the ceramics are reduced by the partially remaining binder, or the characteristics are deteriorated. Furthermore, since the setter is used many times in the firing process, there is a problem that warpage occurs in the setter itself.In order to solve this problem, the thickness of the setter is increased to some extent, and it is difficult to generate warpage. are doing. However, accompanying this, the weight of the setter becomes too heavy, and there is a problem that cracks occur in the molded body during the firing process of the ceramics.

The present invention has been made in view of the above-mentioned problems of the prior art, and has been made to reduce the warpage generated in a sintering process on ceramics, at the same time facilitate the scattering of a binder, reduce cracking defects, and improve the characteristics. It is an object of the present invention to provide a method for producing lead-containing ceramics, which reduces the variation of the ceramics.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for producing lead-containing ceramics, comprising the step of sintering and sintering at least one lead-containing ceramic compact. A plate-like setter is arranged at least at one position above, below, or between the molded bodies, and the composition of the setter is such that the weight ratio of lead does not match the stoichiometric ratio. And It is preferable that the setter has a surface roughness of 5 μm or more or a porosity of 5% or more.

[0006]

The present invention allows the setter to reduce the lead atmosphere in the box by reducing the lead weight ratio of the setter below the stoichiometric ratio. By increasing the weight ratio of lead in the setter to above the stoichiometric ratio, the atmosphere of lead oxide can be intentionally released from the setter, and the lead atmosphere during firing can be controlled.
By setting the porosity of the setter to 5% or more and forming pores in the layer of the setter, it becomes possible for the decomposition gas of the organic binder contained in the ceramic molded body to be scattered through the pores during the firing process. By using a porous setter, the density of the setter can be reduced and the weight of the setter can be reduced. As a result, the load applied to the compact during firing of the ceramics can be reduced. Further, even if the surface roughness is increased, the same effect as that of a large porosity can be obtained.

[0007]

The present invention will be described in more detail with reference to the following examples.
An example in which the present invention is applied to the production of a PZT-based piezoelectric ceramic will be described below. Example 1 A setter is manufactured according to the steps of the method for manufacturing a lead-containing ceramic shown in FIG. The setter has the same composition as the piezoelectric ceramic to be made,
_X (Ti _0.48 Zr _0.52 ) O ₃ +1.0 wt% Nb ₂ O ₅
PbO, TiO ₂ , Zr so that the composition represented by
O ₂ and Nb ₂ O ₅ were weighed and wet-mixed with a ball mill (step a). Here, the lead amount X is 1.01 or 0.9
Each was weighed so that the composition deviated from the stoichiometric ratio as shown in FIG. The obtained slurry is dewatered and placed in an electric furnace for 9 hours.
Calcined at 00 ° C. (step b), and calcined powder and polyvinyl alcohol (PVA) -based binder are 5 wt% based on the calcined powder of the piezoelectric substance, and polymethyl methacrylate (PMMA) -based with a particle size of 50 μm is used. The binder was added in an amount of 3 to 20% by weight based on the calcined powder of the piezoelectric body, and was wet-mixed with a ball mill (step c). The mixed slurry was dried and granulated by a spray drier (step d). The obtained spray powder was formed into a thin plate by press molding (step e).
The molding pressure is 1 ton / cm ² , and the outer dimensions are 35 mm × 35 mm × 2.5 mm in thickness. This molded body is placed in an electric furnace at 1200
Firing at a temperature of 1250 ° C. (step f), porosity 5-60
% Of a porous sintered body was obtained. In order to use this porous sintered body as a setter, it was wrapped with # 400 abrasive powder to obtain flatness.

Next, a compact is produced according to the production process shown in FIG. 1 of the method for producing lead-containing ceramics.
The piezoelectric ceramic to be fired is Pb _x (Ti
_0.48 Zr _0.52 ) O ₃ +1.0 wt% Nb ₂ O ₅ PbO, TiO ₂ , ZrO ₂ , Nb
Each of ₂ O ₅ is weighed and mixed (step a), and calcined in the same manner as in the preparation of the setter (step b). This calcined powder is mixed with a binder (step c), granulated (step d) and pressed at a pressure of 1 ton / cm ^{2 in} the same operation procedure as in the preparation of the setter, except that a PMMA-based binder is not used. Formed (step e), 25mm x 25mm x 0.8mm thick
A molded article having the following dimensions: As shown in FIG. 2, the sintering of the compact was performed by placing the setters 2 and 2 above and below the compact 1 and placing them in a magnesia box at 1200 to 1250 ° C. (step f). In the ceramics of this composition, the dispersion could be reduced by making the upper setter lead-excessive and reducing the lead in the lower setter. Table 1 shows the results of tests on the fired body obtained in this way for cracking defect rate, electromechanical coupling coefficient (Kp) (%), and dielectric constant. Table 1 shows a conventional example of P to be fired.
The results of firing using a setter having the same composition as ZT are also shown in column 5.

[0009]

[Table 1]

Example 2 The composition was changed to Pb _x (Ti _0.20 Zr _0.80 ) O ₃ +1.0 wt.
Example 1 except that the composition represented by% Nb ₂ O ₅ was applied.
In steps a to f, a setter and a molded body were molded, fired, and tested in the same manner as in the above. This composition is close to PZT-based lead zirconate, and is a composition in which lead evaporation is extremely likely to occur.

[0011]

[Table 2]

With such a composition, as can be seen from Table 2, the variation in excess of lead was smaller in both the upper and lower setters. In the above-described embodiment, PZT, which is a piezoelectric material, has been described. However, piezoelectric materials other than PZT, dielectric materials other than piezoelectric materials, insulators, magnetic materials, and other ceramics containing lead, etc. May be applied. Also,
Whether to use a setter with an excessive amount of lead during firing or a reduced setter is selected according to the composition of the ceramic to be fired, the degree of sealing of the box, the convection in the box, and the like. Further, the method of forming the pores in the setter is not only to mix the resin powder, but also to increase the mixing ratio of the organic binder or to mix and mix the foaming agent and the like. In addition, the molding method also shows an example in which granulated powder is pressed by a spray dryer in the examples,
Sheet construction methods such as doctor blade method and pull-up molding method,
In a molding method such as extrusion molding, injection molding, cast molding, or the like, the above-mentioned material that forms pores after firing may be mixed. Further, in the embodiment, the contaminants forming the pores are mixed into the slurry and granulated, but a method of mixing the granulated powder with the resin powder in a dry manner may be employed. Further, in the above embodiment, a single-plate ceramic has been described. However, in a laminate including internal electrodes, the binder is particularly difficult to be scattered, and the remaining of the binder often becomes a problem. It is valid.

[0013]

According to the present invention, the lead atmosphere can be absorbed by the setter by reducing the lead content of the setter from the stoichiometric ratio. By increasing the amount of lead from the stoichiometric ratio, it becomes possible to release the lead atmosphere from the setter. This makes it possible to control the atmosphere in the box during firing by the setter, and at the same time, to reduce warpage. In addition, the atmosphere in the box can be controlled not only in the plane but also in the height direction by controlling the amount of lead setter and the position of the setter. It is possible. Further, since the decomposition gas of the binder is smoothly scattered through the pores, the ceramic fired according to the present invention can eliminate the deterioration and reduction of the ceramic due to the residual binder. Further, with the reduction in the weight of the setter, cracking failure of the ceramics can be reduced.

[Brief description of the drawings]

FIG. 1 is a view for explaining steps of a method for producing a ceramic according to the present invention.

FIG. 2 is a diagram illustrating a firing step of the above steps.

[Explanation of symbols]

 1 molded body 2 setter

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasunobu Yoneda 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd. (56) References JP-A-4-187569 (JP, A) JP-A-4 -321565 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/64

Claims (4)

(57) [Claims] 1. A lead-containing ceramic formed body is
In a method for producing lead-containing ceramics having a step of stacking and sintering at least one sheet, a plate-like setter is disposed at least at one place above, below, or between the formed bodies stacked in the sintering step. Wherein the weight ratio of lead does not coincide with the stoichiometric ratio in the composition of the setter. 2. The method according to claim 1, wherein the lead-containing ceramic is a laminate having an internal electrode. 3. The method according to claim 1, wherein the setter has a surface roughness of 5 μm or more. 4. The method for producing a lead-containing ceramic according to claim 1, wherein the setter has a porosity of 5% or more.