JPH08183665A - Ceramic granule - Google Patents

Abstract

PURPOSE: To obtain a ceramic granule increased in the green strength of a ceramic molding with excellent granule collapsing property, excellent in fluidity in a metallic mold for molding and releasing property therefrom by containing a prescribed quantity of water and an oleate. CONSTITUTION: This ceramic granule contains 1-2wt.% water and the oleate in addition to a ceramic powder and a common binder. The residual water content in the granule is controlled to 1-2wt.% by controlling the drying temp. in a spray dryer. The oleate is added by 1-10 pts.wt. per 100 pts.wt. ceramic powder, in order to act a releasing agent-like or a lubricant-like role. The oleate to be used is a 4-30C partial ester of a polyhydric alcohol containing an ether bond in the molecule. As the ceramic powder, particularly a non-oxide based ceramic powder is effective. The inlet temp. of the spray dryer is controlled to 150-300 deg.C and the outlet temp. is controlled to 50-150 deg.C for granulation. The binder is preferably an acrylic resin.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to ceramic granules. More specifically, the present invention relates to granules for producing a dense sintered body that is well press-molded.

[0002]

2. Description of the Related Art As a method for producing ceramic granules used for producing a ceramic sintered body, a raw material ceramic powder, water as a solvent, a binder, and stearic acid as a release agent are mixed in a ball mill or the like to prepare a slurry. , Dry granulate with a spray dryer. This is molded and sintered to obtain a ceramics sintered body. PVA, acrylic resin, or the like is used as a binder for granulation, but a plasticizer such as PEG is also added to make the granules easily crushed.

[0003]

When PVA or an acrylic resin is used as a granulating binder, the granules are unlikely to be crushed during molding, and it is difficult to obtain a green compact having a high density.
In addition, many voids due to the triple points of the granules and the like exist in the green body, and remain as pores even after sintering, which causes the density of the sintered body to decrease. The pores such as the triple points serve as a source of destruction of the sintered body and cause a decrease in reliability and bending strength of the ceramic. Therefore, it is necessary to increase the pressure at the time of press-molding the ceramics, wear of the mold is quick, the cost of the mold and the cost of manufacturing the sintered body are high, and the cost has been forced to rise.

Further, a plasticizer is also used in order to enhance the action of the binder and reduce the amount of the binder used during granulation, but if too much plasticizer is added, the strength of the green molded product will be insufficient, and during raw processing. There was also a problem that it would be damaged. Further, in order to improve the crushing of granules, the molecular weight is 40,000 to 6,000.
Using PEG specified as 0 as a molding binder,
What obtains a high-density sintered body (Japanese Patent Laid-Open No. 1-29457)
There is also 6), but this also has a problem that it is not suitable for green working of a molded body due to lack of green strength of the molded body. An object of the present invention is to provide a ceramic granule that can be crushed easily at a low pressure, thus increasing the green strength of the ceramic molded body, has excellent fluidity in the molding die, and is easy to uniformly fill. And

[0005]

As a result of various studies to achieve the above object, the inventors have found ceramic granules containing 1 to 2 wt% of water and oleic acid ester in addition to ceramic powder and a general binder.

First, it was found that the crushing of the granules is improved by setting the residual water content of the granules to 1 to 2% by weight, and the crushing of the granules at the time of molding is improved by adding oleic acid ester into the ceramic granules. The green strength of the ceramic molded body is also high, and it has excellent fluidity in the molding die.
Ceramic granules that are easy to fill uniformly.

The residual water content in the granules is adjusted to 1-2 wt% by adjusting the drying temperature of the spray dryer. Two
When the content is more than wt%, the fluidity is lowered due to the adhesion between the granules due to the water content, and the releasability between the mold and the molded product is also lowered, which causes a problem. If it is less than 1% by weight, the granules are hard and are not easily crushed during press molding, so that a high density ceramic sintered body cannot be expected.

In the present invention, the oleic acid ester is contained as a releasing agent or lubricant, and the amount thereof is preferably 1 to 10 parts by weight based on 100 parts of the ceramic powder. If the amount of the oleic acid ester is less than 1 part by weight, a squeak noise is generated during molding, and if it is not added, the granules adhere to each other and the granules having excellent fluidity cannot be obtained. If it exceeds 10 parts by weight, raw workability is deteriorated due to a decrease in green strength of the molded product, and an explosive state may occur during degreasing before sintering.

The oleic acid ester used in the present invention is
It is a partial ester of polyhydric alcohol containing oleic acid and an ether bond in the molecule having about 4 to 30 carbon atoms. Specifically, they are partial esters such as polyethylene oxide, polyglycerin and sorbitan, and these are used alone or as a mixture in the present invention. Moreover, the ester of polypropylene oxide may be mixed.
When the oleic acid ester is a solid or liquid which is difficult to disperse in the water slurry for granulation, it is preferable that the oleic acid ester is thoroughly mixed with the binder and added.

Ceramic powders usable in the present invention include oxide-based and non-oxide-based materials such as alumina, zirconia, titania, mullite, beryllia, sialon, silicon nitride, silicon carbide, aluminum nitride, boron nitride, and ferrite. It is mainly composed of one kind of general-purpose ceramic powder or a mixture thereof. Preferably, the present invention is effective for non-oxide ceramic powders which are difficult to sinter and are required to increase the green density of the molded body. The ceramic powder preferably has an average particle size of 5 μm or less in order to produce a dense sintered body. Further, as the binder that can be used in the present invention, acrylic resin, PVA, PEG,
There are molding binders such as cellulosics, or mixtures of these and copolymerization binders of these monomers.
Binder systems containing acrylic resins are preferred in the present invention. The amount of the binder added is preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the ceramic powder.

As described above, the ceramic powder, the binder, the oleic acid ester, and in some cases, the sintering aid are mixed and made into a slurry with 100 to 300 parts by weight of water, preferably 100 to 300 parts by weight of water, and a spray dryer. Granulate at an inlet temperature of about 150-300 ° C and an outlet temperature of about 50-150 ° C to remove residual moisture in the granules by 1
˜2 wt%. Furthermore, when foaming is observed in the mixed slurry, an antifoaming agent may be added. In addition, when the viscosity of the slurry is high, it may hinder the supply of the slurry when the slurry is sent to the spray dryer. Therefore, a dispersant or the like may be added to make the slurry into granules. Generally, the size of the granules for molding is 50 to 120 μm in average particle diameter.
m. If it is less than 50 μm, the fluidity of the granules is inferior.
If it exceeds 0 μm, the crushing of the granules tends to be insufficient and pores are easily formed in the green body, which is not preferable.

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. Example 1 Silicon carbide powder having an average particle size of 0.6 μm (DUA manufactured by Showa Denko KK
-2) 3 parts by weight of acrylic resin (PB-72 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 1 part by weight of oleic acid ester (R-30 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and boron carbide powder 0.6 per 100 parts by weight of binder. Parts by weight, carbon black powder 2.5
Parts by weight and water were mixed and mixed in a ball mill for 20 hours to obtain a slurry. This slurry is dried at a temperature of 150 ° C.
Then, a granule having an average particle size of 80 μm was obtained with a spray dryer of model number DA-2S-19 manufactured by Sakamoto Giken Co., Ltd. The residual water content of the granules was 1.2 wt%.

The granules were mixed with a 20 mmφ mold to 1.5
Press-molded at a pressure of ton / cm ² and a density of 2.04 g /
A green compact having a cm ³ and a green strength of 60 g / mm ² was obtained. Next, this green body was degreased in an N ₂ atmosphere at 800 ° C. and further sintered in an Ar atmosphere at 2100 ° C. for 5 hours. As a result, a SiC sintered body having a sintered density of 3.12 g / cm ³ was obtained. Table 1 shows the evaluation of the fluidity of the granules of Example 1 and the releasability from the mold.

Example 2 A slurry was obtained in the same manner as in Example 1 except that 2 parts by weight of oleic acid ester was used, and the slurry was granulated with a spray dryer at a drying temperature of 140 ° C. Table 1 shows the residual water content of the granules, the characteristics of the green compact molded under the same conditions as in Example 1, the characteristics of the sintered body sintered under the same conditions as in Example 1, and the fluidity of the granules.

The resulting sintered body was cut into # 100.
0, # 2000, and # 4000 diamond slurries were sequentially polished, # 8000 was used for mirror-finishing, and microscopic observation was performed at 200 times.

Example 3 A slurry was prepared and granulated under the same conditions as in Example 1 except that 2 parts by weight of oleic acid ester was used. Table 1 shows characteristics such as residual water content of the granules.

Example 4 Silicon carbide powder having an average particle size of 0.45 μm (DU manufactured by Showa Denko KK)
A-2) 5 parts by weight of an acrylic resin (PB-72 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 4 parts by weight of oleic acid ester (R-30 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and boron carbide powder 0. 6 parts by weight, carbon black powder 2.
5 parts by weight and water were mixed and mixed in a ball mill for 20 hours to obtain a slurry. Granules were granulated under the same conditions as in Example 1, and the properties such as residual water content of the granules are shown in Table 1. Further, the sintered body was polished under the same conditions as those described in Example 2, and the structure photograph is shown in FIG.

Example 5 Granules were prepared in the same manner as in Example 1 except that the oleic acid ester was changed to 10 parts by weight, and the characteristics such as residual water content of the granules are shown in Table 1.

Comparative Example 1 Silicon carbide powder having an average particle size of 0.6 μm (DUA manufactured by Showa Denko)
-2) 2 parts by weight of an acrylic resin (PB-72 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 2 parts by weight of oleic acid ester (R-30 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and a boron carbide powder 0.6 per 100 parts by weight of a binder. Parts by weight, carbon black powder 2.5
Parts by weight and water were mixed and mixed in a ball mill for 20 hours to obtain a slurry. This slurry is dried at a temperature of 200 ° C.
To obtain granules having an average particle size of 80 μm. The residual water content of the granules was 0.3 wt%.

The granules were made 2.0 using a 20 mmφ die.
Press-molded at a pressure of ton / cm ² and a density of 2.02 g /
A green compact having a cm ³ and a green strength of 88 g / mm ² was obtained. Next, this green body was degreased in an N ₂ atmosphere at 800 ° C. and further sintered in an Ar atmosphere at 2100 ° C. for 5 hours. As a result, a SiC sintered body having a sintered density of 3.09 g / cm ³ could be obtained. FIG. 3 shows a structure photograph of the polished surface of this sintered body under the same conditions as in Example 2 under an optical microscope.

Comparative Example 2 Granulation was carried out under the same conditions as in Comparative Example 1 except that 3 parts by weight of acrylic resin was added. Table 1 shows characteristics such as residual water content of the granules. A photograph of the structure of the obtained sintered body is shown in FIG. 4 (the polishing conditions are the same as in Example 2).

Comparative Example 3 Granulation was carried out under the same conditions as in Example 3 except that 2 parts by weight of stearic acid (Cellosol # 920 manufactured by Chukyo Yushi Co., Ltd.) was added instead of 2 parts by weight of oleic acid ester. Molding was performed using the granules under the pressure shown in Table 1 to obtain the characteristic values shown in Table 1.

Comparative Example 4 A slurry was prepared and granulated under the same conditions as in Example 1 except that the oleic acid ester was not added. Table 1 shows characteristics such as residual water content of the granules.

Comparative Example 5 The same slurry of Example 2 was granulated at a drying temperature of 115 ° C. Table 1 shows characteristics such as residual water content of the granules.

[0025]

[Table 1]

As can be seen from Table 1, it is understood that the present invention has a high density of the sintered body, a high fluidity of the granules, and a good mold releasability from the mold. Further, as can be seen from the photograph of the structure of the sintered body, FIG. 1 and FIG.
Further, it was found from Fig. 4 that it was dense and that there were no large pores, confirming that the collapse of the granules is good.

[0027]

According to the present invention, a dense ceramic sintered body can be obtained because the granules have excellent fluidity and the granules are well crushed.

[Brief description of drawings]

FIG. 1 is an optical micrograph showing the structure of a sintered body produced from the granules obtained in Example 2. (Magnification 200 times)

FIG. 2 is a photograph showing the structure of the sintered body obtained in Example 4. (Magnification 200 times)

3 is a photograph showing the structure of the sintered body obtained in Comparative Example 1. FIG. (Magnification 200 times)

4 is a photograph showing the structure of the sintered body obtained in Comparative Example 2. FIG. (Magnification 200 times)

Claims (1)

[Claims] 1. Ceramic granules containing 1 to 2 wt% of water and oleic acid ester.