JP2614880B2 - Method for producing ceramic granules - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing ceramic granules, and more particularly, to a method for producing ceramic granules having excellent fluidity and moldability.

[Prior Art and Problems to be Solved by the Invention] Conventionally, as means for forming a formed body in a method for manufacturing a ceramic sintered body, there are a slurry casting method, a potter's wheel forming method, an oscillating method, and a dry pressure forming method. Etc. are known. These various molding methods, depending on the liquid content at the time of molding,
The method can be broadly classified into a wet method and a dry method. Of these, according to the wet method, it is necessary to sufficiently dry the formed body after molding, and not only must shrinkage due to drying be taken into consideration, but also defects such as warpage and cracks are likely to occur during drying. On the other hand, the dry method has excellent dimensional accuracy and is an advantageous molding means in this respect.However, when a fine powder is used, the powder is poor in fluidity, so that the powder is uniformly filled into a mold and added. It is difficult to press, and the bulk density of the formed body or the pressure distribution during molding tends to vary, and defects due to bridging are likely to occur in the formed body. The defects at the time of molding remain in the sintered body as they are even after sintering, and cause the physical properties of the sintered body, particularly, the mechanical strength to be significantly reduced. Therefore, conventionally, fine powder raw materials having poor fluidity have been granulated in advance and then subjected to molding. As a typical method of granulating fine powder raw material, a slurry suspension of fine powder is sprayed into a container maintained at a high temperature and granulated while drying rapidly, so-called granulation by spray drying. The law is widely practiced. This method has a uniform particle size distribution, and can easily produce a large amount of spherical and fluid granules in a large amount. On the other hand, when the slurry is dried, a binder (binder) together with water is used. Migration from the inside of the granule to the granule surface causes the binder to concentrate on the granule surface layer, causing a so-called migration phenomenon. As a result, the granule surface layer becomes hard and the press formability decreases, and during granulation sintering, It has the disadvantage that sintering defects occur due to uncrushed granules.

The solubility of the polymer binder in the slurry (slurry) droplets is rapidly reduced, and the polymer binder is precipitated inward to prevent the defects that occur when the slurry droplets are dried. JP-A-58-166926 discloses a device for adding a hardly soluble solvent to form a slurry. However,
This method has disadvantages in that a solvent other than water is used, which still has problems in economy and safety, and that migration of the binder cannot be completely prevented.

[Means for Solving the Problems] The present inventors have conducted intensive studies to solve the above-mentioned disadvantages of the prior art, and as a result, as a binder, a carboxyl group in a molecule which is gelled or hardly solubilized by an acid is contained. Or when using a polymer binder having a salt thereof, it is possible to prevent the binder from migrating to the surface layer of the granules in a simple manner, and to form the ceramic granules with high moldability, particularly, crushability. They have found that they can do this and have completed the present invention.

The present invention relates to a method for producing ceramic granules by spray-drying a slurry suspension comprising a ceramic powder, a polymer binder and a suspension medium, wherein the polymer binder is gelled or hardly acidified in an aqueous solvent as the polymer binder. This method is characterized in that a polymer binder having a carboxyl group or a salt thereof in a molecule to be solubilized is used, an organic acid soluble in water is added to the suspension, and the mixture is spray-dried.

The ceramic powder used in the present invention has a particle size of usually 0.1.
1 to 10 μm, for example, silicon carbide, boron carbide,
Fine powder mainly containing titanium carbide, alumina, mullite, cordierite, zirconia, boron nitride, silicon nitride and the like can be used.

According to the present invention, the slurry suspension preferably has a volume ratio of the ceramic powder in the slurry of 5 to 50%. The reason is that if the volume ratio is lower than 5%, the cost for drying is high and uneconomical, while if it is higher than 50%, the viscosity of the slurry becomes extremely high, so that it becomes difficult to spray.

The binder used in the method of the present invention has a carboxyl group or a salt thereof in the molecule, and in an aqueous medium,
A polymer binder which is gelled or hardly soluble by the addition of an organic acid soluble in water, and has a carboxyl group or a salt thereof (especially an ammonium salt, an amine salt, etc.) in the molecule. , Polyacrylic acid,
Polymethacrylic acid, a copolymer having acrylic acid units,
A copolymer having a methacrylic acid unit, a copolymer having a maleic acid unit, a copolymer having a fumaric acid unit, and the like can be given.

The amount of the polymer binder having a carboxyl group or a salt thereof in the molecule is usually the amount of the ceramic powder.
It is 0.1 to 5% by weight (wt), preferably 1 to 2% by weight.

Water is most frequently used as a suspension medium in the slurry of the method of the present invention, but in addition to water, water and a water-soluble alcohol, or a mixture of water and ketones, methanol, ethanol, acetone, and the like Can also be used.

Further, according to the present invention, a molding aid for exhibiting a lubricating effect at the time of molding to reduce molding defects generated in the formed body can be blended. As the molding aid exhibiting the lubricating effect, carbon wax, magnesium stearate, barium stearate, aluminum stearate, zinc stearate, stearic acid, cellulose acetate, glycerin, polyethylene glycol and the like are used alone or in combination. be able to.

According to the present invention, the above-mentioned ceramic powder, a polymer binder having a carboxyl group or a salt thereof in a molecule, a suspension medium, and a slurry suspension comprising a molding aid, if necessary, are soluble in water. The organic acid is added and mixed, but the acid used is preferably a stronger acid than the acid unit constituting the binder, and the amount used is 0.5 to the constituent acid unit in the binder.
2.0 times equivalent. If the amount of the organic acid soluble in water is too large, the gelation is sufficiently performed, but it is not preferable from the viewpoint of cost.If the amount is too small, the binder does not gel and the effect of the present invention is not obtained. This is undesirable.

Examples of water-soluble organic acids include acetic acid, formic acid, and the like.

The reason that ceramic granules having excellent moldability and sinterability can be obtained by the method of the present invention is that the water-soluble group in the binder is changed to a hardly water-soluble group by adding and mixing a water-soluble organic acid. As a result, the binder is maintained in a gelled or insolubilized state on the surface of the ceramic fine powder, and therefore, even when spray-dried, the gelled binder does not move in the granules together with the moisture, and a so-called migration phenomenon occurs. Is not generated.

According to the present invention, the ambient temperature during spray drying is 100
Preferably it is ~ 250 ° C. The reason for this is that if the ambient temperature is lower than 100 ° C., the time required for drying is long, so that it is practically difficult to perform spray drying, and if the ambient temperature is higher than 250 ° C., a hard shell-like layer is formed on the surface. This is because granules are less likely to be crushed due to the formation of.

According to the invention, the average particle size of the granules is advantageously in the range from 0.02 to 0.5 mm. The reason is that if the average particle size of the granules is smaller than 0.02 mm, the fluidity will be significantly reduced, the bulk density of the formed body and the pressure distribution during molding will vary, and defects caused by bridging in the formed body Is more likely to occur, while if it is larger than 0.5 mm, it is difficult to form a compact and compact shaped body.

The powder bulk density of the granules is 0.6
Advantageously, it is in the range of 1.51.5 g / cm ³ . The powder bulk density is the weight of a given volume of the granules, that is, the solid, the weight per unit volume including the internal voids and the external voids, and the reason for setting the powder bulk density within the above range is as follows. smaller granules than powder bulk density 0.6 g / cm ³ is because it is difficult to mold because the compression ratio is extremely large at the time of molding, while 1.5 g / cm ³ greater granules than a relatively granules granularity There are cases where the distribution is wide or the apparent granule density is high, but in the case of the former, the fluidity deteriorates,
In the latter case, because the crushing strength of the granules is increased, the granules may remain in the same shape without being crushed at the time of press molding and may cause a portion having a significantly low density in the sintered body,
Among them, the range of 0.8 to 1.3 g / cm ³ is more preferable.

It is desirable that the granules have excellent fluidity when filled into a mold, and the present inventor has studied the characteristics of the granules and satisfies the characteristics that the outflow time measured according to JIS-S 2502-66 is within 130 seconds. It has been found that a suitable result can be obtained when performing the above.

According to the present invention, after the granules produced as described above are press-molded into a formed body having an arbitrary shape, the granules are charged into a sintering furnace and sintered to obtain a high-density sintered body. Can be manufactured.

 Next, the present invention will be described with reference to examples and comparative examples.

Example 1 1000 g of alumina fine powder having an average particle diameter of 0.6 μm (manufactured by Showa Denko), an acrylic copolymer resin as a binder (trade name:
(Licabond, manufactured by Chuo Rika) 20 g and water 900 g were mixed for 15 hours using an attritor. 2.1 g of reagent grade acetic acid was added to the obtained slurry of the mixture, and the mixture was further mixed for 3 hours. Next, the obtained mixed slurry was discharged while operating an attritor, and spray-dried to obtain granules. The hot air temperature during the spray drying was about 200 ° C., and the exhaust air temperature was 110 ° C. The average particle size of the obtained dried granules was 90 μm, and the powder bulk density was 0.92 g / cm ³ .

An appropriate amount is collected from the granules, and is then
Temporary molding was performed at a pressure of 0 kg / cm ² , and then molding was performed at a pressing pressure of 500 kg / cm ² . The density of the obtained green body is 2.25 g / cm ³
Met.

When this green compact was fired at 1680 ° C. for 1 hour in an oxidizing atmosphere of an electric furnace, a sintered body having a density of 3.90 g / cm ³ was obtained. Table 1 summarizes the properties of the obtained sintered bodies.

Example 2 A sintered body was obtained in the same manner as in Example 1 except that the pressing pressure was changed to 1000 kg / cm ² . Table 1 shows the characteristic values of the sintered body.

Example 3 A sintered body was obtained in the same manner as in Example 1, except that 1.89 g of formic acid was added as an acid. Table 1 shows the characteristic values of the sintered body.

Example 4 1000 g of silicon carbide fine powder having an average particle diameter of 0.3 μm, carbon as a sintering aid, 20 g of carbon carbide, 6.4 g of boron carbide, 5 g of CMC (manufactured by Daicel Chemical Industries) and 900 g of water as a binder were used for 15 hours using a ball mill. Mixing was performed. 1.2 g of reagent grade formic acid was added to the obtained slurry of the mixture, and the mixture was further mixed for 3 hours.
Next, the obtained mixed slurry was discharged while operating a ball mill, and spray-dried to obtain granules. The hot air temperature during the spray drying was about 200 ° C., and the exhaust air temperature was 110 ° C. The average particle size of the obtained dried granules was 60 μm, and the bulk density of the powder was 0.78 g / cm ³ . Take an appropriate amount from these granules,
Using a metal mold, temporary molding was performed at a pressure of 150 kg / cm ² , and then molding was performed at a pressing pressure of 1000 kg / cm ² . The density of the obtained green body was 1.90 g / cm ³ . When this green compact was fired at 2100 ° C. for 1 hour in a non-oxidizing atmosphere of an electric furnace, a sintered body having a density of 3.12 g / cm ³ was obtained.

 The properties of the obtained sintered body are shown in Table 1.

Comparative Example 1 Granules were obtained in the same manner as in Example 1, except that no water-soluble organic acid was added. The granules of the comparative examples thus obtained are inferior in moldability, especially in crushability, and the sintered body obtained by using the granules has a defect caused by the uncrushed inside of the granules. And its mechanical strength was extremely low.

Claims (1)

(57) [Claims] 1. A method for producing ceramic granules, which comprises spray-drying a slurry suspension comprising a ceramic powder, a polymer binder and a suspension medium, wherein the polymer binder is gelled by an acid in an aqueous solvent as the polymer binder. Hardly soluble
A polymer binder having a carboxyl group or a salt thereof in a molecule is used, and an organic acid soluble in water is added to the suspension in an amount equivalent to 0.5 to 2.0 times the constituent acid of the polymer binder, and then mixed. A method characterized by spray drying.