JPH05840A - Ceramic slurry and production of ceramic structural body by using this slurry - Google Patents

Abstract

PURPOSE:To obtain the ceramic structural body having the sintering density approximate to the theoretical sintering density after calcination by obtaining a ceramic slurry which has good dispersibility of ceramic powder and can form a ceramic molding of a higher density, and calcining the ceramic molding at a relatively low temp. CONSTITUTION:A 1st binder which is soluble in a 2nd solvent and is insoluble in a 1st solvent at need is dissolved in the 2nd solvent which is different from the 1st solvent and thereafter, the ceramic particles are dispersed and spherical particles having the grain size larger than the grain size of the ceramic particles are granulated from the dispersion. The ceramic slurry is then prepd. by dispersing the spherical particles into the 1st solvent. A 2nd binder which is soluble in the 1st solvent and is insoluble in the 2nd solvent is dissolved into the slurry at need and after the ceramic molding is molded from this slurry, the molding is calcined to obtain the ceramic structural body. Since the ceramic particles constituting the spherical particles are fine, the particles are bonded to each other by a flocculation effect and the spherical particles are densely packed to each other. Since the spherical particles have the relatively large grain sizes, the flocculating force between these particles is weak.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic slurry capable of densifying a ceramic compact. Further, the present invention relates to a method for manufacturing a ceramic structure using this slurry.

[0002]

2. Description of the Related Art In an early stage of manufacturing a ceramic structure, the ceramic slurry is treated by a doctor blade method,
In some cases, the ceramic molded body is molded by a cast molding method, an extrusion molding method, or the like. The higher the density of the ceramic molded body is, the more preferable it is because the porosity and the firing shrinkage rate of the sintered body when the ceramic molded body is fired are reduced to reduce the cracks during firing. On the other hand, a ceramic structure for electronic materials is a ceramic powder that is easily sinterable or a ceramic powder to which a sintering accelerator is added in order to achieve downsizing, quality improvement and cost reduction of electronic devices. It is manufactured by sintering each body at low temperature. In order to obtain an easily sinterable ceramic powder, it is necessary to make the ceramic powder uniformly finer to a diameter of the submicron order. A pulverization method in which pulverization is repeated and pulverization is performed with a bead mill or the like, and secondly, a chemical synthesis method such as a metal alkoxide method, a coprecipitation method or a hydrothermal synthesis method can be mentioned.

[0003]

If the powder is infinitely refined by pursuing easy sinterability by the above-mentioned pulverization method or chemical synthesis method, there is a risk that impurities will be mixed in the pulverization method. In both of the chemical synthesis methods, the ceramic powders dispersed in the slurry are easily aggregated due to the increase in the surface activation energy of the powders. Since the cohesive force of this powder is strong and agglomeration occurs randomly, when the ceramic structure is manufactured from finely sinterable ceramic powder, the slurry viscosity increases and gelation easily occurs, or There are problems that it is difficult to uniformly disperse the body, the handling property is poor, the packing rate of the powder when molded is lowered, and the sintered density is difficult to approximate the theoretical density. Further, in the method of sintering the ceramic powder to which the sintering accelerator is added together with the liquid phase, when the sintering accelerator is mixed with the oxide powder by a mill or the like, the accelerator particles become the oxide powder. It is unevenly distributed locally under the influence of agglomerates of the above, and the surface of each powder cannot be uniformly covered. For this reason, even if the sintering accelerator is sufficiently mixed with the oxide powder, the accelerator is likely to segregate in the three pockets formed between the powders, and the sintering promoting effect is not sufficiently exhibited during firing. In order to avoid this point, if a relatively large amount of a sintering accelerator is added, a sintering promoting effect is produced, but in this case, there is a problem that the intended performance of the sintered body is deteriorated. For example, when 20 ppm or more of SiO ₂ is added as a sintering accelerator to high-purity alumina, or when 50 to 500 ppm of MgO is added, the sintering accelerator becomes an impurity when forming a liquid phase and becomes a grain. Since it is difficult for pores in the boundary to disappear, a dense sintered body cannot be obtained. An object of the present invention is to provide a ceramic slurry which has a good dispersibility of ceramic powder and which can densify a ceramic molded body to make a ceramic sintered body dense. A further object of the present invention is to provide a method for producing a ceramic structure capable of firing a ceramic compact at a relatively low temperature and obtaining a sintered density close to the theoretical density after firing.

[0004]

Means for Solving the Problems The present inventors have found that when ceramic fine particles having an extremely fine particle size of less than submicron are made into spherical particles having a larger particle size by using a predetermined binder, etc. In comparison, the present invention has been achieved, focusing on the fact that aggregation of spherical particles is less likely to occur.
The ceramic slurry of the present invention comprises a second solvent different from the first solvent.
If necessary, the first binder, which is soluble in the second solvent and insoluble in the first solvent, is dissolved in the solvent, and then the ceramic fine particles are dispersed, and spherical particles having a larger particle size than the ceramic fine particles are granulated from the dispersion liquid. Then, the spherical particles are dispersed in the first solvent to be prepared. Further, the method for producing a ceramic structure of the present invention is a method in which a ceramic compact is molded from the above ceramic slurry and then fired.

The present invention will be described below. The ceramic fine particles of the present invention are composed of fine powder produced by a known pulverizing method and a chemical synthesis method, and have a particle size in the submicron region from the sintering characteristics,
It is preferably an oxide ceramic powder having a particle size of 0.2 μm or less. The ceramic fine particles will be described below as the first
Disperse in a second solvent different from the solvent. If the first solvent is an organic solvent, the second solvent is, for example, water, and if the first solvent is water, the second solvent is, for example, an organic solution. However, even organic solvents such as methanol and paraffin oil can become the first solvent and the second solvent if they are insoluble in each other. It is preferable to dissolve the first binder, which is insoluble in the first solvent, in the second solvent to increase the bonding force between the ceramic fine particles. Here, the relationship between the first solvent and the first binder is, for example, when the first solvent is an organic solvent, the first binder is an aqueous binder such as polyvinyl alcohol, a polyacrylic acid derivative, a polyol derivative, or carboxymethylcellulose. Is used. As the organic solvent, alcohols having 6 or less carbon atoms, benzene, toluene, xylene and the like are used alone or in combination. On the other hand, when the first solvent is water, an organic solvent-based binder such as polyvinyl butyral, methyl cellulose, an acrylic derivative, an epoxy derivative, or a phenol derivative is used as the first binder. The solution of the first binder is an aqueous solution if the first binder is an aqueous system, and a solution of the organic solvent if it is an organic solvent system. Ceramic fine particles are uniformly dispersed in the solution of the first binder or the second solvent not containing the first binder by using a stirrer, an ultrasonic wave, a mill or the like.

From this dispersion, spherical particles having a particle size larger than that of the ceramic particles are granulated. As the granulation method, the dispersion is sprayed by a nozzle in a heated atmosphere to remove the solvent to form spherical particles, or a spray drying method which has almost the same specific gravity as the dispersion and does not mix with the solvent of the dispersion and There is a method (Japanese Patent Publication No. 3-24255) in which the dispersion liquid is further dispersed in the form of small droplets in a heated high boiling point liquid that does not react with the ceramic fine particles and the solvent is removed in the high boiling point liquid to form spherical particles. The spherical particles are made to have a particle size in the range of about 0.6-5 μm depending on the intended use of the final ceramic structure.

The ceramic slurry of the present invention can be obtained by dispersing these spherical particles in the above-mentioned first solvent. When the powder forms flocs in the solvent, it is preferable to add the dispersant and then disperse the powder using a mixing and dispersing machine such as a mill. Examples of the water-based dispersant include fatty amine salts and quaternary ammonium salts, and examples of the organic solvent-based dispersant include poly-oxyethylene-sorbitan monolaurate. Moreover, you may add a plasticizer as needed. Examples of the plasticizer include dioctyl phthalate, dibutyl phthalate, and other phthalate esters, triethylene glycol, polyalkylene glycol, and other glycol esters. About 0.1 to 3% by weight of a dispersant and about 1 to 4% by weight of a plasticizer are added to 100% by weight of spherical particles.

A second binder, which is different from the first binder and is soluble in the first solvent and insoluble in the second solvent, is added to the prepared ceramic slurry in order to enhance the mechanical strength of the ceramic molded body. May be. Therefore, when the first solvent is an organic solvent, an organic solvent-based binder such as polyvinyl butyral, methyl cellulose, an acrylic derivative, an epoxy derivative, and a phenol derivative is used as the second binder, and the first solvent is water. Second, if
An aqueous binder such as polyvinyl alcohol, a polyacrylic acid derivative, a polyol derivative, or carboxymethyl cellulose is used as the binder.

The ceramic slurry thus obtained is formed into a ceramic compact by a doctor blade method, a casting molding method, an extrusion molding method or the like, and after being formed into a predetermined shape, at 1200 to 1600 ° C. under atmospheric pressure. It is fired into the desired ceramic structure.

[0010]

In the spherical particles dispersed in the ceramic slurry, since the ceramic fine particles forming the spherical particles are fine, these fine particles are bonded to each other by the aggregating action, whereby the spherical particles form voids between the fine particles. It is packed tightly without. On the other hand, since the spherical particles have a relatively large particle size, the cohesive force is weak and the dispersibility is good.

[0011]

As described above, the ceramic slurry of the present invention has excellent handling properties because the cohesive force of the dispersed spherical particles is relaxed, and the spherical particles are composed of fine ceramic fine particles. Therefore, the obtained green body can be sintered at a low temperature, and when fired, a ceramic structure having a sintered density close to the theoretical density can be obtained.

[0012]

EXAMPLES Next, examples of the present invention will be described together with comparative examples. <Example> 2 g of polyvinyl alcohol was dissolved in 150 mL of water to prepare an aqueous polyvinyl alcohol solution. The average particle size produced by hydrothermal synthesis in this aqueous solution is about 0.06 μm.
50 g of barium titanate was added and stirred with a stirrer to uniformly disperse the fine barium titanate in the aqueous solution. This dispersion is passed through a nozzle of a sprayer for 120 to 15
It was sprayed into a drying chamber maintained in the 0 ° C range. The water content of the sprayed particles was removed in a floating state, and spherical particles having an average particle size of about 1.1 μm expanded by polyvinyl alcohol were obtained at the bottom of the drying chamber. On the other hand, a polyvinyl butyral organic solution in which the polyvinyl alcohol was insoluble was prepared by dissolving 8 g of polyvinyl butyral in 32 g of an organic solvent in which toluene and ethanol were mixed at a ratio of 6: 4. 40 g of the powder consisting of the spherical particles was dispersed in this organic solution to obtain a barium titanate slurry. A film of this slurry was dried by a doctor blade method to remove the dispersion medium, thereby forming a green sheet having a thickness of 0.5 mm. When the density of this green sheet was measured, it was 3.78 g / c.
It was m ³ . Furthermore, this green sheet is 200-50
After calcination at a temperature of 0 ° C. to completely remove polyvinyl alcohol and polyvinyl butyral, it was baked at a temperature of 1200 ° C. under atmospheric pressure for 1 hour at which the ceramic particles were completely sintered. The density of this sintered sheet was 5.9 g / cm ³ .

Comparative Example 40 g of barium titanate having the same particle size as in the example was dispersed in 40 g of the same polyvinyl butyral organic solution as in the example to obtain a barium titanate slurry. This slurry was molded into a green sheet in the same manner as in the example, and its density was measured.
It was 31 g / cm ³ . Further, the green sheet was calcined and fired in the same manner as in the example to obtain a sintered sheet. The density of this sintered sheet was 5.4 g / cm ³ . The density of the sintered sheet of the comparative example was much smaller than the theoretical density of 6.0 g / cm ³ , while the sintered density of the sintered sheet of the example was close to the theoretical density.

Claims (5)

[Claims] 1. Ceramic fine particles are dispersed in a second solvent different from the first solvent, spherical particles having a larger particle size than the ceramic fine particles are granulated from the dispersion, and the spherical particles are dispersed in the first solvent. Ceramic slurry made by. 2. The ceramic slurry according to claim 1, wherein a first binder that is soluble in the second solvent and insoluble in the first solvent is dissolved in the second solvent. 3. The ceramic slurry according to claim 2, wherein a second binder that is different from the first binder and that is soluble in the first solvent and insoluble in the second solvent is dissolved. 4. The first spherical particles together with a dispersant.
The ceramic slurry according to claim 1 or 2, which is dispersed in a solvent. 5. A method for producing a ceramic structure, which comprises forming a ceramic compact from the ceramic slurry according to claim 1 and then firing the compact.