JP2003192453A - Method for granulating ceramic powder and ceramic granule using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain ceramic granules which are hardly affected by the environment such as temperature and humidity of the manufacturing processes of ceramics so as to obtain uniform dimensions of final sintered products in the manufacturing processes. <P>SOLUTION: A wax emulsion is added as a molding assistant to the ceramic powder and ceramic granules are obtained by a mixing and granulation method. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention uses oxide ceramic powders such as alumina, mullite, cordierite, ferrite, and dielectrics, which are added with a molding aid and granulated, followed by die press molding and rubber press molding. In the manufacturing process of ceramics, which is carried out to obtain a sintered body by firing them,
The present invention relates to a granulation method for obtaining ceramic powder granules used for molding and ceramic granules obtained thereby.

[0002]

2. Description of the Related Art The characteristics required for granules of ceramic powder used in die press molding and rubber press molding are
It has fluidity, proper strength of the molded product, good crushability of the granules, good degreasing property during firing, etc. Spray drying by dry was common.

In this granulation method, a ceramic powder is slurried, and then polyvinyl alcohol (PVA), polyethylene glycol (PEG), an acrylic water-soluble binder, or an emulsion type binder is added as a molding aid and spray-dried. Was.

[0004]

It is an important subject to make the final sintered body uniform in size in the ceramic manufacturing process. The dimensional stability can be achieved by controlling the shrinkage rate during firing, but the shrinkage rate is greatly affected not only by the firing conditions and the adjustment of the ceramic powder, but also by the environment after granulation. In other words, the shrinkage rate during firing changes due to changes in the green density and dimensions of the compact due to changes in the storage environment of ceramic granules, the environment during compaction, and the storage environment of compacts, and as a result, the dimensions of the sintered compact vary. To do. The main cause of this variation is due to the moisture absorption of the binder due to the use of the water-based binder as a molding aid.
This is an unavoidable problem as long as a water-based binder is used as a molding aid.

In order to solve this problem, it is necessary to keep all the environments related to the manufacturing process constant.
It is too costly and unrealistic. It may be possible to use a non-aqueous solvent and a binder, but a facility for spray drying and a solvent recovery treatment facility are required, which causes a rise in manufacturing cost. It is also possible to use a wax emulsion, which loses hygroscopicity after drying, in spray drying, but it is very difficult to wash once it is dried, and large equipment such as a spray dryer main body and a tank for agitating slurry is used. Was not suitable for producing a wide variety of products by spray drying. Due to these problems, it is often the case that the frequency of dimensional inspections is increased or the sintered body is processed later, but it is not an effective method because it increases the manufacturing cost. .

[0006]

According to the present invention, a wax emulsion is used as a molding aid, and ceramic powder is granulated using a stirring granulator which is easy to wash, so that the environment of the manufacturing process is not affected. The ceramic granules capable of obtaining a sintered body having a stable size can be manufactured at low cost.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings.

Ceramic powder having a predetermined composition and particle size adjusted in advance is granulated by stirring granulation while adding a wax emulsion. The outline of a continuous stirring granulator is shown in FIG. A predetermined amount of ceramic powder is introduced through the ceramic powder introduction port 2 and a predetermined amount of molding aid is introduced through the molding aid introduction port 1. The forming aid is supplied into the apparatus through the forming aid spray port 3, moves to below the slit 5 while being uniformly mixed with the ceramic powder on the stirring disk 4, and granulates between the granulating blade 6 and the casing 7. Then, the granulated granules are discharged from the ceramic granule discharge port 8. The supply rate of the ceramic powder can be appropriately set within the range of 50 kg to 300 kg per hour. The stirring speed needs to be adjusted according to the supply rate of the ceramic powder, but from 800 rpm to 2000
A range of rpm is preferred.

Further, in the case where a relatively small amount of granulation is carried out, the method shown in FIG.
You may use the batch type stirring granulator shown in FIG. A predetermined amount of ceramic powder is introduced through the ceramic powder introduction port 2 and a predetermined amount of molding aid is introduced through the molding aid introduction port 1. The forming aid is supplied into the apparatus through the forming aid spray port 3, moves while being uniformly mixed with the ceramic powder on the stirring disk 4, and is granulated by the granulating blade 6.

The reason for using the stirring granulation is that in the fluidized bed granulation, the oxide ceramic powder is hard to fluidize and the granulation itself is difficult to proceed, and the size of the granules obtained by the tumbling granulation is large, which is suitable for the purpose. There is no thing. The stirring and granulating apparatus may be a commercially available one, but a continuous or batch stirring and granulating machine is selected according to the required production amount in consideration of the installation area, equipment cost, cleaning property and production efficiency.

The addition ratio of the wax emulsion to the ceramic powder may be appropriately determined according to the application.
Generally, the solid content of the emulsion is preferably in the range of 2% by weight to 8% by weight. If it is less than 2% by weight, the strength of the molded product is weak, and if it is more than 8% by weight, the degreasing property in the firing step is deteriorated. The average size of the obtained granules is 50 μm to 250 μm, preferably 70 μm to 150 μm. If it is smaller than this, the fluidity is impaired, and if it is larger than this, voids between granules remain after molding.

The type of wax emulsion must be carefully selected because it affects the strength of the molded product, the crushability of the granules, and the processability of the molded product. Either paraffin wax or microcrystalline wax, or those Mixtures or compounded waxes made from these waxes are suitable.

The wax is roughly classified into natural wax and synthetic wax. The former includes animal / vegetable wax, mineral wax, and petroleum wax, and the latter includes polyethylene wax and other synthetic waxes. Paraffin wax and microcrystalline wax are classified into petroleum wax. Paraffin wax is composed of hydrocarbons having a carbon number distribution of about 20 to 40 and a molecular weight of about 300 to 550, which is separated and refined from a vacuum distillation distillate, and usually 90%.
The above is normal paraffin. Microcrystalline wax, on the other hand, has a carbon number distribution of about 30 to 60 and a molecular weight of about 500 to 800, separated and refined from the vacuum distillation residue oil.
Consisting of hydrocarbons, mostly isoparaffins and cycloparaffins. The wax emulsion is obtained by emulsifying and dispersing these waxes in water. Due to these characteristics, in general, paraffin wax gives softer granules, and microcrystalline wax gives harder granules. Further, a mixed product of these waxes and a compounded wax obtained by using these waxes as raw materials can be used depending on the characteristics of the target granules.

There are various wax melting points, but it is preferable that the melting point is 60 ° C. or higher. When the wax having a melting point lower than 60 ° C. is used, the strength of the obtained granule is weak, and it is often not suitable as a granule for ceramics molding.

The reason for using the wax emulsion is that it has no hygroscopic property after drying. Some wax emulsions may use hygroscopic emulsifiers,
This is not suitable for the purposes of the invention. From the viewpoint of hygroscopicity, for example, acrylic emulsion is also suitable, but the obtained granules are too hard, and thus the molded product is not easily crushed and is not suitable as ceramic molding granules.

The hygroscopicity of the ceramic powder obtained by the granulation method of the present invention can be evaluated by the weight change when the granules or the molded product are left in a constant environment. Here, the ceramic granules of the present invention preferably have a weight change of 0.3% or less at 20 ° C. and 80% relative humidity, based on the weight at 20 ° C. and 30% relative humidity. . This is because if it is more than 0.3%, it has an adverse effect on the original purpose of uniforming the dimensions of ceramics.

The granulation method of the present invention can be applied to oxide ceramics such as alumina, mullite, cordierite, ferrite and dielectrics. Further, products using the ceramic powder obtained by the granulation method of the present invention, applications include semiconductor manufacturing equipment parts, wear resistant parts, sliding parts, jigs, substrates, electronic parts, dielectric resonator parts, etc. Can be mentioned.

[0018]

[Example] As a molding aid, the melting point is 50 ° C, 62 ° C, 6
A commercially available paraffin wax emulsion having a temperature of 9 ° C. and a microcrystalline wax emulsion having a melting point of 70 ° C. and 83 ° C. were used. Alumina, which is a typical oxide ceramic, having an average particle diameter of about 2 μm was used as the ceramic powder.

Granulation was carried out by using the continuous stirring and granulating apparatus shown in FIG. 1 so that each wax emulsion was added in an amount of 5% by weight based on the solid content of the ceramic powder. The stirring speed of the stirring granulator is 1300 rp
m, and the material supply rate was 200 kg / Hr. The contents are summarized in Table 1.

Next, a molded body was prepared using the obtained granules, and the change in size due to temperature and humidity and the change in weight due to moisture absorption were examined.

The hygroscopicity was evaluated by measuring the weight of granules weighing 15 g for 1 t.
The molded article of 25mmφ molded using at / cm ^2, 20 ℃
The weight change rate when left at 30% for 16 hours and then left at 20 ° C. and 80% for 16 hours was calculated based on 20 ° C. and 30%. The outer diameter 25
After the molded body of mm was left at 20 ° C./30% for 16 hours and then left at 20 ° C./80% for 16 hours, the dimensional change rate of the outer diameter was determined on the basis of 20 ° C./30%. For the evaluation of the strength of the molded body, a test piece of 5 mm × 5 mm × 50 mm is 1 t
/ Cm ² and molded by 3 point bending with a span of 30 mm. The results are summarized in Table 2.

[0022]

[Table 1]

[0023]

[Table 2]

From this result, the embodiment of the present invention (No. 1,
2, 4 to 6) were excellent in that the weight change rate of the molded product was as small as 0.3% by weight or less and the dimensional change rate was also small.
In Example (No. 1), a wax emulsion having a melting point of 50 ° C. was used as a molding aid. Compared to this, a wax emulsion having a melting point of 60 ° C. or higher was used,
The examples (NO. 2, 4 to 6) are superior in terms of the strength of the molded body.

On the other hand, No. For Nos. 7 and 8, an aqueous PVA solution having a saponification degree of 88% was used as a molding aid, and the aqueous PVA solution was added to a solid content of 3% by weight by using a spray dryer and a continuous stirring granulator. , Stirring speed is 1300 rpm, material supply speed is 200 Kg / H
Granulation was carried out at r. It is a comparative example in which the obtained granules were evaluated in the same manner as in the examples. In this comparative example, the rate of change in weight of the molded body was as large as 0.3% by weight or more, and the rate of dimensional change was also large.

No. No. 3 used a commercially available molding aid, a paraffin wax emulsion having a melting point of 62 ° C., and added a wax emulsion to a solid content of 5% by weight using a fluidized bed granulator. This is a comparative example in which granulation was performed, but a satisfactory granule could not be obtained because a fluidized bed could not be formed.

[0027]

According to the present invention, by adding a wax emulsion to a ceramic powder as a molding aid and obtaining ceramic granules by a stirring granulation method, it is possible to sinter with a stable size without being influenced by the environment of the manufacturing process. It is possible to inexpensively manufacture ceramic molding granules capable of obtaining a body.

[Brief description of drawings]

FIG. 1 is a diagram showing a continuous stirring granulator used in the method of the present invention.

FIG. 2 is a diagram showing a batch-type stirring granulator used in the method of the present invention.

[Explanation of symbols]

1: Molding aid input port 2: Ceramic powder charging port 3: Molding aid spray port 4: Stirring disk 5: Slit 6: Granulated feather 7: Casing 8: Ceramic granule outlet

Claims (4)

[Claims] 1. A method for granulating a ceramic powder, which comprises adding a wax emulsion as a molding aid to the ceramic powder and performing agitation granulation. 2. The method for granulating ceramic powder according to claim 1, wherein the wax emulsion is a paraffin wax, a microcrystalline wax, a mixture of these waxes, or a compounded wax prepared by using these waxes as raw materials. . 3. The melting point of the wax emulsion is 60 ° C.
It is above, The granulation method of the ceramic powder of Claim 1 or 2 characterized by the above-mentioned. 4. A method for granulating a ceramic powder according to claim 1, which has a relative humidity of 30 at 20.degree.
% Relative to the weight in the environment, 20% relative humidity at 80%
The rate of change in weight in the environment is 0.3 wt% or less, a ceramic granule.