JPH03193143A - Beads for dispersing ceramic slurry and preparation of ceramic slurry - Google Patents

Abstract

PURPOSE:To reduce the mixing of impurity with the composition of a ceramic body composed of a sintered body by constituting dispersing beads used when a ceramic raw material is formed into a slurry of an acrylic resin having a predetermined mol.wt. CONSTITUTION:Dispersing beads used when a ceramic raw material is formed into a slurry is composed of an acrylic resin (e.g. polyalkyl methacrylate or an acrylic resin containing two or more kinds of alkyl methacrylate, alkyl acrylate and acrylic acid) having an mol.wt. of 1-1,000,000. When the beads composed of the acrylic resin are used in the preparation of a slurry, even when the beads are abraded and the material thereof is mixed with the ceramic slurry, said material is burnt in an incinerating or baking process because it is org. matter and no effect is exerted on the composition of a ceramic body composed of a sintered body. As mentioned above, the mixing of impurity with the composition of the ceramic body composed of the sintered body is reduced and it can be prevented that the specific resistance of a semiconductor ceramic body becomes high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to dispersion beads used to obtain a ceramic slurry of ceramic raw powder when manufacturing ceramic electronic parts, and a ceramic slurry using the same. Regarding the manufacturing method.

[Conventional technology]

Ceramic bodies are widely used in electronic components such as ceramic capacitors, but recently there has been a demand for ceramic bodies that have improved electrical characteristics and further reduce variations in their electrical characteristics. This improvement in properties and reduction in variation can be achieved by strictly controlling the composition of the ceramic body.

Generally, ceramic bodies for electronic components are made of BaTiO3, for example.
, 5rTi05 and other titanates such as TiO2, 5io2,
Oxides such as Bi2O5 are added together with water, etc., and wet mixing is carried out.
A ceramic slurry is prepared by dispersion, and this slurry is dehydrated and dried and then calcined to form a titanate with a predetermined metal atomic composition ratio. After being mixed with a combustible binder and molded, the binder is burned out and the
Main firing is performed at 0° C. to obtain a sintered ceramic body. Alternatively, the above slurry is dehydrated and dried, mixed with the above binder, granulated, then molded, and gradually heated to 1350°C.
The temperature is raised to about 100 degrees and fired at this temperature to obtain a sintered ceramic body.

When producing ceramic slurry through this series of steps, the part of the dispersing means that comes into contact with the ceramic raw material powder is worn out, and the worn material is mixed into the finished ceramic slurry, resulting in the final product. For example, the metal composition ratio of the metal titanate in the ceramic body is often made different from the originally designed composition value. Therefore, what is used as this dispersion means is extremely important.

A ball mill has long been known as a dispersing machine that performs this dispersion. In this method, ceramic raw material powder, water, or other dispersion medium are placed in a cylindrical or spherical container along with hard balls, and the entire container is rotated for a predetermined period of time, and the ceramic raw material powder is dispersed by friction between the balls and against the inner wall of the container. It is intended to be crushed and dispersed in water, etc. In this case, the ball is selected from a material that is resistant to abrasion and that even if the material is abraded and mixed into the ceramic slurry, it will have little effect on the composition ratio of the resulting ceramic body. For example, non-oxide balls such as natural stone (mainly composed of silica), agate, alumina porcelain balls, and 5iC1Si3N4 are used.

However, recently, compact and high-performance products such as ceramic capacitors are required, and for this purpose, ceramic products are also required to have a dense structure, and improved dispersibility is also required when preparing ceramic slurry. Along with this, bead mills are increasingly being used as continuous production systems to improve productivity.Bead mills have a rotating shaft with multiple rotary plates mounted spaced apart inside a cylindrical container. Furthermore, beads with a diameter of 0.5 to 51 mm are placed in 50 to 70% of the space inside the cylindrical container, and the raw materials for the ceramic slurry are introduced into the container, and the rotating shaft is rotated at high speed to reduce the friction between the beads and the beads. Dispersion is performed by friction with the inner wall of the container.This bead mill improves dispersion efficiency in a short period of time, making it possible to continuously obtain highly dispersible ceramic slurry.

[Problem to be solved by the invention]

However, the friction between the beads and the friction between the beads and the inner wall of the container, which are the main factors for the high dispersibility of bead mills, causes the beads to wear out when using alumina beads, for example.
The worn material enters the ceramic slurry as an impurity and changes the composition of the ceramic body as described above. Even if glass beads or titania beads are used, a satisfactory ceramic body cannot be obtained. Currently, zirconia beads made of 70 partially stable zirconia have the best wear resistance and have come into use. However, this is very expensive, for example about 5 to 10 times more expensive than alumina beads.

SUMMARY OF THE INVENTION An object of the present invention is to provide a dispersion bead for a ceramic slurry that can reduce the influence of impurities on the composition of a sintered ceramic body and can be provided at low cost, and a ceramic slurry using the same.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides dispersion beads used when slurrying ceramic raw materials with a molecular weight of 1 to 1.
The present invention provides ceramic dispersion beads characterized by being made of 1 million acrylic resin. The present invention also provides a ceramic slurry manufacturing method for manufacturing ceramic slurry using the beads for dispersing ceramic slurry.

[Function] When beads made of acrylic resin are used in the production of ceramic slurry, even if the beads are worn out and the material is mixed into the ceramic slurry, it is an organic substance and will not be used in the subsequent calcination or firing process. It is burned out and does not affect the composition of the ceramic body of the resulting sintered body.

〔Example〕

Next, the present invention will be explained in detail.

Example 1 This BaTiO31 using high purity BaTiO3 as the main raw material
With respect to mole, Bi2O30,002 mole, TiO20,
Accurately weigh 0.02 mol of 004% JL/and 5i, add 1.5 times the total weight of cypress water to it, and mix (roughly) using a method that does not use balls or beads, such as a hatch type mixer. dispersion) was performed.

Next, this crude dispersion was mixed with polymethyl methacrylate (molecular weight 2
A ceramic slurry was obtained by performing a dispersion treatment under the following conditions in a bead mill using beads consisting of 0,000 yen).

Bead mill internal volume: 51 Peas mill rotation speed: 800 revolutions per minute Bead input amount: 3.5ρ Bead diameter: 1.5 fl Slurry discharge amount: 27 per minute! Note that the beads were molded by a so-called spray manufacturing method in which molten resin is blown out from a pressure nozzle and rapidly cooled.

After that, it goes through a wet sieve and dehydration drying process in the same way as the normal manufacturing method of ceramic fired bodies, and is mixed with water and a binder made of polyvinyl alcohol resin using a seeder, granulated, and molded into a predetermined shape at 1350°. The sintered body is BaTiO3.
A semiconductor ceramic body was produced.

I on both sides of the semiconductor ceramic body thus obtained
An electrode was formed by rubbing an n-Ga alloy and used as a measurement sample. The resistance value of this sample was measured (25° C.), the specific resistance was calculated, and the results are shown in the table below.

Comparative Example 1 Ceramic slurry was prepared in the same manner as in Example 1, except that instead of using a bead mill, a ball mill using agate boulders, which is normally used as a wet mixing method for raw materials in the production of BaTiO3 semiconductor resistors (PTC thermistors), was used. I got it.

This ceramic slurry was also treated in the same manner as in Example 1 to produce a BaTi0 semiconductor ceramic body, and the specific resistance was calculated in the same manner as in Example 1, and the results are shown in the table below.

Comparative Examples 2 to 5 Ceramic slurry was obtained in the same manner as in Example 1, except that the beads were made of the same material as listed in the table below, and from this a semiconductor ceramic was obtained in the same manner as in Example 1. The results of calculating the specific resistance are shown in the table below.

As is clear from the above table, the specific resistance of the semiconductor ceramic body obtained using the beads of Example 1 is smaller than that of the others. This is a process in which the dry powder of ceramic slurry is granulated with a binder, molded, and then fired. Even if the worn beads are mixed into the ceramic slurry, they are burned out together with the binder at a low temperature (200 to 500°C). However, this is thought to be because it does not remain in the fired ceramic body and therefore does not increase the resistance value.

Although polymethyl methacrylate was used as the acrylic resin in the above examples, similar results can be obtained with alkyl methacrylate resins having a molecular weight of 1 to 1 million, such as polyethyl methacrylate and polyisopropyl methacrylate.

Similar results can be obtained with a copolymer containing two or more of alkyl methacrylate, alkyl acrylate, acrylic acid, etc. and having a molecular weight of 1 to 1,000,000.

〔Effect of the invention〕

According to the present invention, since the ceramic slurry, which is a dispersion of ceramic raw material powder, is obtained using acrylic resin beads, even if the worn material of the beads is mixed into the slurry, it will not be removed during the subsequent firing process. Since this is burnt away and no residue remains, there is less contamination of impurities in the fired ceramic body, and for example, it is possible to prevent the resistivity of the semiconductor ceramic body from becoming high and to obtain a stable resistivity. Also, it is cheaper than zirconia beads,
It is cost-effective and has great economic effects.

December 25, 1999

Claims (5)

[Claims] (1) Beads for dispersing ceramic slurry, characterized in that the dispersing beads used when slurrying ceramic raw materials are made of an acrylic resin with a molecular weight of 1 to 1 million. (2) The beads for dispersing ceramic slurry according to claim 1, wherein the acrylic resin is polyalkyl methacrylate. (3) The beads for dispersing ceramic slurry according to claim 1, wherein the acrylic resin is a copolymer of at least two monomers: alkyl methacrylate, alkyl acrylate, and acrylic acid. (4) The beads for dispersing ceramic slurry according to claim 2 or 3, wherein the alkyl is lower alkyl. (5) A method for producing a ceramic slurry using the beads for dispersing a ceramic slurry according to any one of claims 1 to 4.