JPS61287433A - Production of ceramics pellet - Google Patents

Abstract

PURPOSE:To obtain the titled pellets having a superior moldability by blending 2 kinds of liquids which are slightly soluble each other as the suspending medium solution and whose temperature difference between the boiling points of two liquids is >=20 deg.C in a specified volume ratio and by using the two kinds of liquids in the production of pellets by spray-drying. CONSTITUTION:In the production of pellets by spray-drying the slurry in which ceramics powder such as silicon carbide, etc., an binding agent such as gum arabic, etc., and the suspending medium solution are mixed each other, water is used as the low boiling point liquid of the suspending medium solution and one kind out of benzyl alcohol, etc. is used as the high boiling point liquid of the suspending medium solution, both of them are blended in 100:5-120 volume ratio for its use. The resultant pellets have a superior fluidability and moldability. In addition, the desirable atmospheric temperature of spray-drying is 100-250 deg.C and the preferable volume ratio of the ceramics powder in the suspension slurry is 5-50%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application in M Industry] The present invention relates to a method for producing ceramic granules, and particularly the present invention relates to a method for producing ceramic granules with excellent fluidity and moldability.

[Conventional technology]

BACKGROUND ART Conventionally, as means for forming a formed body in a method for producing a ceramic sintered body, methods such as slurry filling molding, potter's wheel molding, rocking molding, and dry pressure molding are known. The above-mentioned molding means can be broadly classified into wet molding and dry molding means depending on the I content and amount at the time of molding.

Among these methods, wet molding means requires sufficient drying of the formed body after molding, and not only shrinkage due to drying must be taken into account, but also defects such as warping and cracking are likely to occur during drying. On the other hand, dry molding is an advantageous molding method as it has excellent dimensional accuracy, but when using fine powder, it is difficult to fill the mold uniformly and pressurize it because the powder has poor fluidity. This is difficult and may cause variations in the bulk density of the formed body or the pressure distribution during molding, and defects due to pre-riding may easily occur in the formed body. These molding defects remain in the sintered body even after sintering,
This causes a significant decrease in the physical properties, especially the mechanical strength, of the sintered body. Conventionally, when molding a formed body using fine powder raw materials, the fluidity is poor, so the powder raw materials are granulated in advance to improve the fluidity. Raw materials with improved quality are used.

As the granulation method, for example, a granulation method using spray drying is widely known.

[Problem that the invention seeks to solve]

The above-mentioned spray drying granulation method is a method in which a slurry-like suspension is sprayed into a container maintained at the same temperature and granulated while extremely rapidly drying. Although it has the advantage of being able to easily produce large quantities of granules with good sexual characteristics, it shrinks during drying and reduces the apparent granule density.
The disadvantage is that the granules tend to become hard, and the press formability deteriorates. In addition,
The apparent granule density is the weight per unit bulk volume, and the bulk volume is the volume including the solids occupied in the granules and internal voids.

[Failure to solve the problem]

Therefore, as a result of various studies to solve the above-mentioned problems, the present inventors mixed ceramic powder, a binder, and a suspension medium to form a slurry-like suspension, and then spray-dried the mixture. In the method for producing granules, two types of liquids are used as the suspending medium and have a boiling point difference of at least 20°C, and the boiling point of the liquid is at least 20°C. We have newly discovered that ceramic granules with extremely excellent fluidity and moldability can be produced by using a liquid containing 5 to 120 parts by volume of a liquid with a high completed.

The present invention will now be described in detail.

According to the present invention, two types of liquids are used as the suspending medium liquid and have a boiling point difference of at least 20°C, and the boiling point It is necessary to use a liquid containing a liquid with a high value of 5 to 120 parts by volume.

The reason why two types of liquids that are poorly soluble in each other and have different boiling points are used as the suspension medium is that the droplets of the slurry-like suspension that are sprayed are dried by the surrounding hot air. By first evaporating the liquid component with a lower boiling point and then evaporating the liquid with a higher boiling point, the relative drying rate can be slowed down, and the two liquids can interact with each other. Because it is poorly soluble, during the drying process, the liquid with the higher boiling point of the two types of liquids remains in the droplets for a relatively long time, suppressing shrinkage during drying and preventing the granules from becoming excessively hard. This is because it is possible to produce granules with good moldability.

Further, the reason why it is necessary that the difference in the respective boiling points is at least 20°C is that if the difference in boiling points is less than 20°C, the relative drying rate will not be slowed down sufficiently, which is the objective of the present invention. This is because it is difficult to produce granules with good moldability, and it is particularly preferable that the difference in boiling point is 50°C or more.

The reason for using all the liquids in which 5 to 120 parts by volume of liquids with higher boiling points are mixed with 100 parts by volume of liquids with lower boiling points is that the ratio of the two types of liquids is outside the above range. In this case, it is difficult to obtain the effect of mixing two types of liquids.

By the way, as a granulation method using a spray drying method for the purpose of producing granules with good moldability, there is
-166926 [When granulating an inorganic raw material powder made into a slurry using a water-soluble or water-uniformly dispersible polymeric material as a particle binder by spray drying, A method for granulating an inorganic raw material powder, which comprises adding a solvent in which the entire molecular material is difficult to dissolve to water to form an inorganic raw material powder and a polymer binder gold slurry. ”
The invention related to is disclosed. However, whereas the invention described in the above-mentioned publication uses a solvent that is compatible with water and is difficult to dissolve the polymeric binder, the present invention uses two solvents that are poorly soluble in each other as a suspending medium. This method is completely different in that it uses different types of liquids.

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

According to the present invention, water is used as the liquid with a lower boiling point among the two types of liquids, and benzyl alcohol-A/, 1-octatool, propyl benzoate, or 2-dibutylaminoethanol is used as the liquid with a higher boiling point. -pI7) It is preferable to use at least one selected from among them.

According to the present invention, the ceramic powder includes silicon carbide, boron ash, titanium ash, alumina, mullite, cordierite, zirconia, aluminum nitride, boron nitride,
Fine powder containing mainly silicon nitride or the like can be used.

Binders used in the present invention include, for example, starch, dextrin, gum arabic, casein-Vie, N
a-carboxymethylcellulose, methylcellulose,
Cellulose acetate, glycerin, polyvinyl afrecol, polyvinyl butyral, polyvinyl methyl ether,
Polyacrylic acid amide, polyethylene glycol, tannin m, ia paraffin, wax emulsion, ethyl cellulose, polyvinyl acetate, phenol resin, etc. can be used alone or in combination, but according to the present invention, the binder has a boiling point to the liquid on the lower side of: t! 11 and is soluble in liquids with higher boiling points can be particularly advantageously used.

The amount of the binder used in the present invention is preferably 1 to IO parts by weight per 100 parts by weight of the ceramic powder.

Further, according to the present invention, a molding aid may be added to exhibit a lubricating effect during molding to reduce molding defects that occur in the formed body. As the molding aid that exhibits the lubricating effect, carbowax, magnesium stearate, barium stearate, aluminum stearate, salivary lead stearate, stearic acid, cellulose acetate, glycerin, polyethylene glycol, etc. may be used alone or Can be used in combination.

According to the present invention, the atmospheric temperature during spray drying is 100°C.
Preferably, the temperature is ~250°C. This is because if the atmospheric temperature is lower than 100°C, it will take a long time to dry and it is practically difficult to spray dry the ground. This is because the granules become difficult to crush due to the formation of layers.

According to the invention, it is advantageous for the average particle size of the granules to be in the range from 0.02 to 0.5 degrees. The reason for this is that if the average particle size of the granules is smaller than 0.02u, the fluidity will drop significantly, causing variations in the bulk density of the formed body and pressure distribution during molding, and causing burrs in the formed body.

This is because defects due to ging are likely to occur, and on the other hand, if the diameter is larger than 0.6, it is difficult to mold a compact and complex shaped product.

The powder bulk density of the granules
nity ) is advantageously in the range 0.6 to 1.59/cd. The bulk density of the powder is the weight of a certain volume of granules, that is, the weight per unit volume including solids, internal voids, and external voids, and the reason why the bulk density of the powder is within the above range is as follows. Powder bulk density is 0.6 f
This is because granules smaller than 1/e are difficult to mold because the compression ratio during molding becomes significantly large, while granules larger than 1.5 Vd are difficult to mold when the particle size distribution of the granules is relatively wide or when the In some cases, the granules have a high viscosity, but in the former case, the fluidity deteriorates, and in the latter case, the pressure oil strength of the granules is strong, so they do not collapse during press molding and the shape of the granules is maintained. This is because it may remain in the sintered body and cause areas with extremely low density, especially 0.
A range of 8 to 1.8'I/cTi is more preferable.

It is desirable that the granules have excellent IN and m properties when filled into a mold, and as a result of research on the characteristics of the granules, the inventor found that the outflow time measured according to JIS-32502-66 is within 180 seconds. It has been found that suitable results can be obtained when the characteristics are satisfied.

According to the present invention, the granules produced as described above are press-molded into a formed body of an arbitrary shape, and then charged into a sintering machine and sintered, resulting in a high-density sintered body. can be manufactured.

Next, the present invention will be explained with reference to Example P and a comparative example.

Example 1 96.2% by weight consists of β-type crystals, contains 088% by weight of free return element, 0.18% by weight of oxygen, 14.2 knots
Expanded silicon fine powder with total specific surface area of f/I 200Of/
Commercially available 200-mensch selective boron grains were crushed, classified by particle size, and the specific surface area was determined to be 21. ．． 4FvfK, a mixture of prepared expanded boron powder 6.4mm and Reso-I type phenol resin 140y with a fixed element content of about 50% by weight, benzyl Realco-z+/600& and stearic acid. 4Of
and Wednesday 2.71! 15 by adding all and using attritor.
Time mixing was performed. Then, the slurry of the slurry mixture was discharged while the attritor was running and spray-dried to obtain granules. Note that the hot air temperature during this spray drying was about 165°C, and the exhaust air temperature was about 90°C.

The particle structure of the obtained dry granules was as shown in the scanning electron micrograph of FIG. 1, with an average particle size of 70 μm and a powder bulk density of 0.97 y/cti.

An excess amount was collected from the granules, and a metal press was used to remove the excess amount.
Temporary molding was carried out at a pressure of 15 Llc-, and then molding was carried out using an isostatic press machine at a pressure of 8 L/cj. The density of the resulting form was found to be 1.86 f/cd.

The resulting green body was charged into a Tammann type firing furnace [7, the temperature was raised to 2140° C. in an argon gas current, and sintered by holding for 1 hour.

The resulting sintered body had a density of 8.151//c-. This sintered body was processed into a rod shape of 8X8X80sn, and the final V was polished using a diamond grindstone with a diameter of 1 μm.
When the 8-point bending strength was completely measured under the condition of l/gin, it had an average strength of 82.7 kg//Nai at room temperature.

On the fracture surface of the sample whose bending strength was measured, no defects due to collapse of the granules were observed.

Example 2, Comparative Example 1 A mixture slurry was prepared in the same manner as in Example 1, but by changing the amounts of benzifle alcohol and water as shown in Table 1 [7 Granules were created and a sintered body was obtained. Ta.

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

Table 1 The granules of Comparative Example 1 were poor in formability, particularly in crushability, and the sintered bodies obtained using these granules had internal defects due to the granules not being crushed. The strength was extremely low.

Example 8 Same as Example 1, but 1-butanol, propyl benzoate and 2-butanol instead of benzyl alcohol! Granules were made using rare aminoethanol 17, and a sintered body was produced.

All of the obtained granules had excellent formability, and all of the sintered bodies produced using all of these granules still had good strength.

〔Effect of the invention〕

As described above, according to the method of the present invention, it is possible to easily produce granules with extremely excellent moldability, which was difficult to obtain with conventional granulation methods, and is extremely useful industrially. .

[Brief explanation of the drawing]

FIG. 1 is a scanning photon micrograph (400x magnification) showing the particle structure of the granules described in Example 1.

Claims (1)

[Claims] 1. Mixing a ceramic powder, a binder, and a suspending medium,
In a method for producing granules, which is formed into a slurry-like suspension and then spray-dried, the suspending medium includes two types of liquids that are poorly soluble in each other and have a boiling point difference of at least 20°C, A method for producing ceramic granules, characterized in that a liquid is used in which 5 to 120 parts by volume of a liquid having a higher boiling point is mixed with 100 parts by volume of a liquid having a lower boiling point. 2. Claim 1 in which the liquid with a lower boiling point is water
Manufacturing method described in section. 3. The manufacturing method according to claim 1 or 2, wherein the liquid with a higher boiling point is at least one selected from benzyl alcohol, 1-octanol, propyl benzoate, and 2-dibutylaminoethanol. . 4. The atmospheric temperature during the spray drying is 100 to 250.
The manufacturing method according to any one of claims 1 to 3, wherein the temperature is .degree. 5. The manufacturing method according to any one of claims 1 to 4, wherein the slurry-like suspension has a volume ratio of ceramic powder in the slurry of 5 to 50%.