JP2823629B2 - Method for removing impurities from powdery lead compounds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a lead compound, particularly a trace amount of metallic impurities contained in a lead monoxide (PbO) powder or a lead tetroxide (Pb ₃ O ₄ ) powder. More particularly, the present invention relates to a method for removing impurities in a powdery lead compound for removing Fe, Ni, Cr and the like.

(Prior Art) In recent years, with the progress of the electronics industry, miniaturization of electronic components has been rapidly promoted, and multilayer ceramic capacitors have been widely used for electronic circuits. Was. This capacitor is made of a dielectric material mainly composed of BaTiO _3, the dielectric material 1250 ° C. to 1350
Since the material must be fired at a high temperature of ℃, the conditions for using this material as a stacked ceramic capacitor are palladium (melting point: 1555 ° C) or its alloy that does not melt at the firing temperature and does not oxidize. It will be used as an internal electrode. However, the above-mentioned metal or its alloy is a well-known expensive noble metal and is not suitable for mass consumption. Therefore, it has been proposed to use relatively inexpensive materials such as Ag and Ni for the internal electrodes. In this case, a material that is sintered at a low temperature of 1000 ° C. or less is selected as the material to be sintered as the dielectric. Such materials include, for example, Pb (Fe 1/2 Nb 1/2) O ₃ , Pb (FE 2/3 W 1/3) O ₃ , Pb (M
g 1/3 Nb 2/3) O ₃ . The source of lead in the manufacture of these materials is usually litharge (lead monoxide; PbO) or lead tin (lead tetroxide; Pb ₃ O ₄ ), which is lead metal; Pb ( (Purity 99.95% or more) is air-oxidized, passed through lead oxide (Pb ₂ O), and manufactured by a dry method.

(Problems to be Solved by the Invention) Since equipment used for such production is generally made of iron or stainless steel, a very small amount of Fe, Ni, Cr is contained in the material during the production process. It cannot be avoided that metal impurities such as are mixed. As before, 10
In the case of a material fired at 00 ° C. or higher, for example, PZT, PLZT, etc., since the metal impurities become oxides, they did not affect the product characteristics after firing, but 1000
In the case of a lead-based porcelain material sintered at a temperature of not more than ℃, depending on the particle diameter of the metal impurities, there is a possibility that the product characteristics may be impaired.

That is, according to the results of research and investigation by the inventor, usually, among the above metal impurities, those having a diameter of about
In the following sintering, it is oxidized and becomes insulating, but the particle size
Above μm, it is difficult to completely oxidize,
It has been found that it has electrical conductivity, adversely affects product characteristics, and leaves problems such as shortened product life.

(Object of the Invention) The present invention has been made based on the above circumstances,
By classifying the powder material at a boundary of 3 μm, metal impurities contained in the powdery lead compound, which have a particle size that has an adverse effect after sintering, are removed. It seeks to provide a way.

(Means for Solving the Problems) For this reason, in the present invention, the powdery lead compound is sieved using a screen having a mesh of a predetermined mesh capable of classifying particles at a boundary of 37 ± 3 μm. This removes impurity particles larger than 3 μm.

(Effect) By this, the product after sintering is free from the influence of the impurities, and the impurities bring about such advantages that the insulating property is completely maintained, the product characteristics are maintained at a high level, and the life can be maintained long.

(Example) Hereinafter, the impurity removing method of the present invention will be specifically described with reference to the drawings. In the present invention, a screen is used as a method for classifying a powdery lead compound.
This is based on the following examination results. Generally, the following classification means are known.

(1) Screening of dry powder by vertical vibrating screen (2) Classification of dry powder by air classifier (3) Screening of wet slurry by vertical vibrating screen Although it is advantageous, a powder having a very high adhesion, such as a lead compound, has a limit of sieving with an opening of 74 μm, which is expected in the present invention.
If the opening size is set for classification of about ± 3 μm, clogging occurs and sieving cannot be performed. Since the second classification means does not use a sieve, there is no danger of clogging. However, since it is air classification, it is impossible to completely classify it at a boundary of 37 μm. In addition, since a large amount of air is used, a large-sized bag filter is required, so that an increase in the size of the apparatus cannot be avoided. In the third classification means, in order to sieve the slurry of the lead compound, even in the case of a mesh having an opening of 37 μm,
Can be completely sieved. For this reason, this third classification means can be employed in the present invention, but the slurry under the sieve requires the steps of dewatering, drying, and pulverizing, and is industrially unsuitable.

For the purpose of simply removing iron, there is a method of removing impurities using a magnetic field, but it is not suitable for removing non-magnetized metals such as Ni and Cr. Therefore, the apparatus shown in the figure was adopted as an apparatus suitable for employing the method of the present invention. That is, the screen 1 having a mesh network capable of classifying particles at a boundary of 37 ± 3 μm used in the present invention is formed in a cylindrical shape, is arranged horizontally, and is slightly twisted around the drive shaft 2 passing through the center. Is provided. At an end of the screen 1, a supply chamber 4 for introducing a powdery lead compound into the screen 1 is formed.
A discharge chamber 5 for discharging the wastewater is formed. An opening 4a is provided in the upper part of the supply chamber 4, from which the powdery lead compound is introduced. Further, a screw 6 positioned in the supply chamber 4 for feeding in the axial direction is provided.
Are provided on the drive shaft 2. Screen 1
On the lower side of the receiving chamber 7 for receiving the sieved material
Are arranged. In the figure, reference numeral 8 denotes a drive motor,
Reference numeral 9 denotes a speed reducer that reduces the speed when power is transmitted from the drive motor 8 to the drive shaft 2. Reference numeral 10 denotes a vibration feeder, which brings the powder into the supply chamber 4 from above the opening 4a. In this configuration, the area sieved by the screen 1 is larger than the whole size, and the powdery lead compound is reduced by the stirring blade 3 rotating at high speed.
The high-frequency vibration is generated in the screen 1 by the stirring blade 3 which is pressed into the inside and further rotates at high speed, and clogging of the screen is prevented.

Examples (1) and (2) in which the powdery lead compound according to the present invention was sieved using such an apparatus are as shown in the table below. For comparison, a case in which a screen having the same aperture is used in a conventionally known vibrating screen (Sato type vibrating screen 1000D-IS, manufactured by Koei Sangyo Co., Ltd.) is illustrated.

As is clear from the above results, efficient use of the powdery lead compound can be realized by using a screen (aperture: 37 ± 3 μm) in the form of the above embodiment.

(Effect of the Invention) As described above, according to the present invention, by suppressing the particle size of impurities to 40 μm or less, when firing at 1000 ° C. or less as a porcelain material, mixed metals such as Fe, Ni, and Cr are mixed. It is possible to completely oxidize impurities and remove electrical conductivity, thereby making it an insulator. By this treatment, the quality when used in a magnetic capacitor or the like can be ensured and the life of the product can be kept long. Further, by employing this method, for example, a lead oxide for producing an optical glass having a very high purity can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic structural view of an apparatus showing an embodiment of the present invention, and FIG. 2 is a sectional view of the same. 1 ... screen, 2 ... drive shaft, 3 ... stirring blade, 4 ...
... supply chamber, 5 ... discharge chamber, 6 ... screw, 7 ... receiving chamber, 8 ... drive motor, 9 ... reduction gear, 10 ... vibration feeder.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seizaburo Muraki 4049-1 Naoshima-cho, Kagawa-gun, Kagawa Pref. Naoshima Chemical Co., Ltd. (Int.Cl. ⁶ , DB name) C01G 1/00-57/00

Claims (2)

(57) [Claims] 1. A method for removing impurities in a powdery lead compound, wherein the powdery lead compound is sieved using a screen having a mesh of a predetermined mesh to remove impurity particles larger than 37 ± 3 μm. 2. A powdery lead compound is introduced into a horizontally supported cylindrical screen having a mesh of predetermined mesh, and sieved while stirring with a stirring blade provided in the cylindrical screen.
3. The method for removing impurities in a powdery lead compound according to claim 1, wherein the impurity particles larger than μm are removed.