JP2003063874A - Method for manufacturing ceramic spherical body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a ceramic spherical body having a high density and a high sphericity. SOLUTION: In a method to form spherical bodies from a ceramic powder, spherical bodies obtained by spraying and drying a slurry prepared by mixing the ceramic powder and a solvent are used as core particles and further processed to form spherical bodies having larger diameters than the core particles. The resulting spherical bodies are sintered.

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 a spherical ceramic material for use in a media stirring mill or the like.

[0002]

2. Description of the Related Art Inorganic materials such as alumina, zirconia, silica, and silicon nitride are generally supplied as fine powders for fine ceramics in the form of fine powder having a particle size distribution in the range of submicron to several tens of microns. Many of these fine powders are produced by pulverization. In the case of pulverization of fine ceramics, the purity of the pulverized fine powder has a great influence on the quality and performance of the final product, so it is necessary to avoid contamination due to the inclusion of impurities in the production process of the fine powder.
Therefore, ceramic balls used in agitation mills and the like that are widely used for crushing, mixing, and dispersing materials are desired to be hard and hardly generate powder due to collision between balls and abrasion. Further, in recent years, the tendency of raw material powder to be made into fine powder has been increasing in various industrial fields, and ceramic balls used in agitation mills and the like have a tendency to have a smaller particle size in order to improve pulverization efficiency. Conventionally, a rolling granulation method has been generally known for the production of ceramic balls. Further, as the rolling granulator, a rotary dish type granulator, a rotary drum type granulator or the like is used to mold the small-sized spherical particles. The tumbling granulation method is generally performed in the same granulating apparatus from the formation of nuclei to a desired particle size while sprinkling a binder on a dry powder or a moist powder.
In addition, when only fine powder is used as the raw material powder, the efficiency of forming the particles that form the core of the molded sphere becomes low, so a method is generally used in which coarse powder is mixed as core particles in the fine powder. ing. As a method of providing core particles to this rolling granulation method, there is a method of manufacturing core particles by a stirring granulation method. However, in the production of ceramic balls of 1 mm or less, which has been increasingly demanded in recent years, the required core particles are required to have high sphericity, so that the productivity is very poor and it is difficult to produce them in large quantities. is there.

It is said that the productivity of the rolling granulation method largely depends on the generation rate of core particles. Further, in the rolling granulation method, it takes a huge amount of time to grow from a raw material powder having a size of several microns to the size of core particles, resulting in poor productivity.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the drawbacks of the prior art and to provide a method for producing a ceramic molded spherical article which enables simple continuous mass production.

[0005]

The present invention has the following constitution in order to solve the above problems. That is, in a molding method of molding ceramic powder into spherical particles, the ceramic powder is mixed with a solvent to form a slurry, and then the molded spherical product obtained by spraying and drying the slurry is used as core particles to form the molded spherical particles. Shaped spherical object with a diameter larger than that of the object,
This is a method for producing a ceramic spherical material by sintering the molded spherical object.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below.

According to the present invention, in a molding method for molding ceramic powder into spherical particles, the ceramic powder is mixed with a solvent to form a slurry, and then the slurry is sprayed and dried to obtain a molded spherical particle as a core particle. As the shaped sphere, the shaped sphere having a diameter larger than that of the shaped sphere is sintered.

In the present invention, the ceramics used as the raw material for the ceramic powder are zirconia, alumina,
At least one selected from silicon nitride, silicon carbide, zircon or a mixture thereof can be used,
Above all, in order to avoid contamination of impurities due to damage or wear of ceramic spherical objects during the fine powder manufacturing process, high strength,
It is preferable to use zirconia having high toughness.

As the solvent to be mixed with the ceramic powder, water, alcohol, or various organic solvents can be used. Among them, water is preferable from the viewpoint of environment and ease of handling.

The shape of the core particles in the present invention is preferably a true sphere, for example, the core particles themselves are not crushed or crushed during the growth process in which they are put into a rolling granulator and granulated. It is desirable to have molded body strength. In order to give the core particles sufficient strength for molding and to enable continuous mass production, molding by a spray dryer can be preferably used in the present invention.

The spray dryer is not particularly limited, and the core particles can be obtained by drying with a normal spray dryer in which the sprayer is a disc type or a nozzle type. It is preferable to use the disc method when obtaining fine core particles, and it is preferable to use the nozzle method when obtaining coarse core particles. Further, the granulation conditions are not particularly limited, but it is preferable to adjust the slurry in consideration of the shape of the generated core particles and the strength of the molded body.

The ceramic powder slurry to be charged into the spray dryer can be prepared by, for example, suspending the ceramic powder in water. As a suspension method here, a method using a ball mill or a method using an attritor can be used.

In the present invention, the ceramic powder can be manufactured by a neutralization method, a hydrolysis method, etc., and the calcined ceramic powder has an average particle size of 0.001 mm.
It is also possible to use the ceramic powder slurry obtained by finely pulverizing to a certain degree as it is.

If the concentration of the ceramic powder slurry is too low, it becomes a porous compact having a high porosity, and the compact strength of the core particles becomes low, which is not preferable. Therefore, the concentration of the ceramic powder slurry is preferably 20% by weight or more.

It is also possible to add the binder dispersed by the tumbling granulation method at the time of preparing the slurry to produce the core particles, and uniformly disperse the binder in the core particles to perform the tumbling granulation.

In the present invention, if a spray dryer is used, core particles having an average particle size of 0.5 mm or less can be obtained. Further, in granulation by a tumbling granulator, the smaller the core particles, the longer it takes to obtain a finished product. Therefore, it is desirable to use core particles having a size suitable for a desired finished product particle size. Here, the average particle diameter is obtained by averaging the longest diameter and the shortest diameter of 100 spheres.

The core particles obtained in the present invention are classified by using a sieve and supplied to a rolling granulator which is the next step.
Particles outside the desired particle size range can be returned to the core particle forming step and used again.

The rolling granulation is not particularly limited,
General granulation conditions are applied, and the raw material powder and water as a binder can be added to the core particles put into a tumbling granulator to form a desired size. The diameter of the core particles is 20 to 90% of the diameter of the molded spherical product desired by rolling granulation.
Is preferred. Thereafter, depending on the solvent used, for example, water is preferably dried at 50 to 150 ° C., and zirconia is preferably 1300 to 1500.
C., and preferably alumina for 1500 to 17
A ceramic spherical material can be obtained by sintering at 00 ° C.

The density of the spherical ceramics in the present invention is preferably 95% or more of the theoretical density. If it is less than 95% of the theoretical density, voids are present inside the spherical substance and wear due to insufficient strength occurs, so that it is not preferable because it causes contamination of impurities when used in the production of fine powder.

The sphericity of the ceramic spherical material in the present invention is preferably 1.05 or less.

The sphericity of the ceramic spherical material in the present invention means the ratio of the maximum diameter to the minimum diameter (maximum diameter / minimum diameter) of the spherical material. When the sphericity exceeds 1.05, abrasion of the sphere occurs, which is not preferable because it causes contamination of impurities when used in the production of fine powder. More preferably, the sphericity is 1.03 or less.

The defect retention rate of the spherical ceramics in the present invention is preferably 5% or less. The defect retention rate of the ceramic spheres in the present invention means that the spheres are fixed in resin and ground to divide the spheres into halves, and the defects inside the spheres are observed with a microscope.
It refers to the ratio of the number of spherical objects in which fine void defects are present, out of 0. If the defect retention rate exceeds 5%, abrasion due to insufficient strength occurs, so that it is not preferable because it causes contamination of impurities when used in the production of fine powder. The defect retention rate is more preferably 3% or less.

The ceramic spheres obtained by the present invention can be preferably used for media applications such as media agitation mills for producing ceramic fine powders of barium titanate etc. in the field of electronic materials.

[0024]

EXAMPLES Next, the present invention will be specifically described with reference to examples. The physical property values were measured by the methods described below. (1) Density of ceramic spheres The density of the obtained ceramic spheres is about 20 in a container.
It was measured by the Archimedes method. (2) Sphericity of spherical ceramics For the sphericity, the obtained spherical ceramics were placed in a container and magnified 45 times with an Olympus stereomicroscope to measure the maximum diameter and the minimum diameter. (3) Defect retention rate of ceramic spheres The defect retention rate is determined by melting a thermoplastic resin on a metal plate heated to 200 ° C, cooling the metal plate with the obtained ceramic spheres placed, and using a resin. After fixing the ceramic spheres, the ceramic spheres were ground and halved, and magnified 50 times with a Nikon optical microscope to observe defects inside the ceramic spheres.

Example 1 A zirconia powder slurry 20 having a slurry concentration of 45% by weight was prepared by mixing zirconia powder with water and then mixing with an ordinary attritor using zirconia balls for 2 hours.
kg was adjusted. Next, 20 kg of the adjusted zirconia powder slurry was molded at a rotation speed of 4000 rpm using a commercially available disk-type spray dryer. When the molded spheres were classified, the diameter was 0.125 to 0.175 m.
Core particles having a distribution of m were obtained in a yield of about 50%.

Next, the core particles were introduced into a rotary dish type granulator having a pan having a diameter of 600 mm, and the addition amount of the raw material powder and water was adjusted under a constant rotation speed of the pan, to obtain a molded spherical product. All became zirconia molded spheres having a diameter of around 0.5 mm.

Next, the obtained zirconia molded spherical product was
It sintered at 400 degreeC and obtained the zirconia spherical object. The sphericity of about 100 spheres of this zirconia is 1.00 to 1.0.
The average value was 1.01. The density of the zirconia spheres are 6.02 g / cm ^3, was 98% of theoretical density 6.1 g / cm ^3. Next, the obtained zirconia spheres were fixed in a resin, the zirconia spheres were halved by grinding this, and the defects inside the spheres were observed with a microscope. There were fine void defects, and the defect retention rate was 3%.

Example 2 A zirconia powder slurry 20 having a slurry concentration of 80% by weight was prepared by mixing zirconia powder and water and then mixing for 2 hours with a normal attritor using zirconia balls.
kg was adjusted. Next, 20 kg of the adjusted zirconia powder slurry was molded at a rotation speed of 4000 rpm using a commercially available disk-type spray dryer. When the shaped spheres were classified, core particles having a distribution of diameters of 0.2 to 0.25 mm were obtained in a yield of about 50%.

Next, the core particles were introduced into a plate type granulator having a pan having a diameter of 600 mm, and the addition amounts of the raw material powder and water were adjusted under a constant rotation speed of the pan. All of the objects were zirconia molded spheres having a diameter of around 0.6 mm.

Next, 1 part of the obtained zirconia molded spherical product was used.
It sintered at 400 degreeC and obtained the zirconia spherical object. The sphericity of about 100 spheres of this zirconia is 1.00 to 1.0.
The average value was 1.01. The density of the zirconia spheres are 6.02 g / cm ^3, was 98% of theoretical density 6.1 g / cm ^3. Next, the obtained zirconia spheres were fixed in a resin, the zirconia spheres were halved by grinding this, and the defects inside the spheres were observed with a microscope. There were fine void defects, and the defect retention rate was 3%.

Comparative Example 1 Zirconia powder was placed in a plate type granulator having a pan having a diameter of 600 mm, and the zirconia powder was rolled at a constant rotation speed of the pan,
Molding was performed by adjusting the amounts of the raw material powder and water added so that the diameter of the molded spherical product was around 0.5 mm, but the shape of the obtained molded spherical product was not spherical.

[0032]

According to the manufacturing method of the present invention, it is possible to mass-produce heavy ceramic spheres having a high sphericity and the same spherical diameter.

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Claims (5)

[Claims] 1. A molding method for molding a ceramic powder into a spherical material, which comprises mixing the ceramic powder with a solvent to form a slurry, and then spraying and drying the slurry as a core particle. A method for producing a ceramic spherical object, which comprises forming a molded spherical object having a diameter larger than that of the molded spherical object and sintering the molded spherical object. 2. The density of the spherical ceramics is 9 of the theoretical density.
It is 5% or more, The manufacturing method of the ceramic spherical object of Claim 1 characterized by the above-mentioned. 3. The method for producing a spherical ceramic material according to claim 1, wherein the spherical ceramic material has a sphericity of 1.05 or less. 4. The method for producing a ceramic spherical object according to claim 1, wherein the defect retention rate of the ceramic spherical object is 5% or less. 5. A raw material for spherical ceramics is zirconia.
The method for producing a ceramic spherical article according to any one of claims 1 to 4, which is at least one selected from alumina, silicon nitride, silicon carbide, zircon, and a mixture thereof.