JP2001039715A - Production of zirconia fine powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce zirconia powder to obtain a compound for injection molding which has excellent flowability and which does not require a large amount of a binder even though it has a large specific surface area. SOLUTION: The zirconia fine powder is obtained by drying and calcining a hydrated zirconia sol containing a zirconium salt or a mixture of a stabilizer and the hydrated zirconia sol containing the zirconium salt. In this method for producing the zirconia fine powder, the hydrated zirconia sol containing the zirconium salt, or the mixture of the stabilizer and the hydrated zirconia sol containing the zirconium salt is dried and calcined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing zirconia fine powder used for producing zirconia ceramics. In particular, the compound has good fluidity in a compound of an organic binder and zirconia powder. An object of the present invention is to provide a method for producing zirconia fine powder capable of obtaining a compound exhibiting good molding characteristics in injection molding.

[0002]

2. Description of the Related Art An injection molding method is well known as one of the methods for producing a zirconia sintered body. In this injection molding method,
A mixture of an organic binder obtained by mixing zirconia fine powder and various organic substances, that is, a compound as a molding composition,
This is injected into a mold to form a green molded body, which is then degreased and fired to obtain a zirconia sintered body.

As a method for producing zirconia fine powder, a hydrated zirconia sol is dried by heating and hydrolyzing an aqueous solution of a zirconium salt or an aqueous solution in which a stabilizer such as Y, Ce or Ca coexists. Method (hydrolysis method)
A method of neutralizing an aqueous solution of a zirconium salt in which a zirconium salt and a stabilizer coexist, and drying and calcining the obtained precipitate (neutralization method) is widely known. It is also well known that hydrated zirconium sol is filtered through an ultrafiltration membrane or the like, thereby simultaneously filtering and concentrating impurities to increase drying efficiency.
Further, according to this method, since unreacted components of the hydrolysis reaction together with impurities can be removed at the same time, zirconia fine powder having a high purity and a high conversion can be produced.

[0004]

However, in molding by injection molding, it is an important condition that the compound has good fluidity. In injection molding, a compound melted in a high-temperature cylinder of an injection molding machine is injected into a cavity in a mold. At this time, when a compound having insufficient fluidity is used, the molding pressure is increased. Since the compound injected into the mold is not evenly distributed to every corner, uneven stress distribution occurs in the molded body, resulting in uneven density of the molded body. As a result, the molded body is said to have sink marks Cause a phenomenon. In an extreme case, the molten compound is not sufficiently filled in the cavity, and a molding defect called a short circuit may occur.

Conventionally, compounds containing ceramic powder such as zirconia tend to have a high yield value against shear stress and are not excellent in fluidity as compared with plastics. Therefore, various methods for improving the liquidity have been taken. For example, the simplest method is to increase the compounding ratio of the binder in the compound. However, in this case, the powder density of the molded body is reduced, and the shrinkage deformation after firing is increased, so that a highly accurate sintered body cannot be obtained, which is not preferable. Further, among the constituent components of the binder, it is conceivable to increase the amount of strongly plastic components such as an acrylic resin and a fatty acid. However, generally, these components generate a large amount of heat at the time of degreasing and cause cracks in the molded body after degreasing. It is not preferable because the number of things increases.

Next, there is a method of forming a compound using zirconia powder having a small specific surface area (hereinafter, referred to as a BET specific surface area) by a BET method. When producing zirconia powder, a powder having a small BET specific surface area can be produced by increasing the calcining temperature in the calcining step. In such powders, the average particle size is large,
Since the interaction between particles becomes small, the fluidity of the compound is improved, but the density of the sintered body tends to decrease, which is not always preferable.

Generally, in order to improve the characteristics of the sintered body, for example, the density of the sintered body and the sinterability at a low temperature, a powder having a large BET specific surface area and monodispersed particles is desirable.

[0008] As described above, the fluidity of the compound is an important factor influencing the molding characteristics in injection molding, and the compound was prepared using high-purity zirconia powder prepared by the above-mentioned hydrolysis method or neutralization method. Although the compound has excellent properties of the sintered body, there is a problem that the compound has insufficient fluidity and is not suitable for use in injection molding.

It is an object of the present invention to provide a method for producing a zirconia powder which provides a compound for injection molding which has a high specific surface area, does not require a large amount of binder, and has excellent fluidity.

[0010]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive studies on a method for producing zirconia powder. The inventor has found that sintering can provide a zirconia powder that gives a compound for injection molding having excellent fluidity while maintaining a high BET specific surface area, and has accomplished the present invention.

Hereinafter, the present invention will be described in detail using a hydrolysis method as an example.

In the present invention, a hydrated zirconium sol obtained by hydrolyzing an aqueous solution of a zirconium salt is used as a zirconia source. More specifically, a 0.3 mol / l solution of zirconium oxychloride was heated and boiled under normal pressure to obtain a hydrated zirconia sol having a zirconia conversion of 98% or more. As a result of observation with an electron microscope, it was found that the sol was mainly composed of hydrated zirconia particles having a diameter of 1,000 nm.

The hydrated zirconia sol thus obtained is concentrated by ultrafiltration. By repeating this filtration several times, concentration is performed and at the same time 2% contained in the liquid.
The following unreacted Zr components and impurities can be filtered out. At this time, the amount of unreacted Zr component was monitored by ICP emission analysis of the filtrate, and the zirconia addition rate was finally determined.
A 100% hydrated zirconia sol was obtained.

The concentration of the obtained concentrated sol was adjusted so that the solid concentration in the solution became 35%, and dried using a spray drier. Here, the solid content refers to ash remaining after drying the hydrated zirconia sol at 1000 ° C. for 2 hours. A feature of the present invention is that the zirconium salt is added again to the concentrated sol thus obtained. The zirconium salt to be added is not particularly limited to zirconium oxychloride, but may be zirconium chloride, zirconium nitrate, or the like. Alternatively, a method of leaving unreacted Zr components in the concentrated sol using a hydrated zirconium sol having a low zirconia conversion rate in hydrolysis may be used, but in this case, the amount of remaining Zr must be adjusted accurately. There are difficult disadvantages.

Thus, a concentrated sol containing a zirconium salt is prepared and spray-dried using a spray drier to prepare a dried zirconium salt-containing hydrated zirconium sol powder. Next, the dried powder is calcined at 850 ° C. for 2 hours in an air atmosphere. Heating rate is about 100 ° C
/ Hour. Further, the calcined powder is washed with water by a decantation method, and then pulverized using a ball mill.
The pulverized powder thus obtained is dried again with a spray drier and used for preparing a compound.

For the kneading of the zirconia powder and the organic binder, a usual pressurized biaxial kneader was used. The temperature is preferably from 80 ° C to 160 ° C because combustion and volatilization of the organic binder occur at a high temperature, and softening of the binder is hindered at a low temperature. As the kneading time is longer, the fluidity of the compound is improved, but a practical time of 1 to 5 hours is preferable. As the organic binder, an acrylic binder, a styrene-based binder, a fatty acid, and the like, which are used in usual injection molding of ceramics, can be used.

The mixing ratio of the organic binder to the zirconia powder was about 20% by weight, which corresponds to about 50% by volume. However, in the case of the present invention, the preparation of the compound is for use in the evaluation of liquidity described below, and the details of the composition and the preparation method are not important as long as they are constant and general.

The fluidity of the compound was evaluated according to JIS K 7210
Melt flow rate (MFR) measurement as specified in
As the sample, a powder having a uniform particle size is desirable, and a compound obtained by classifying a mechanically pulverized compound is suitable.
The sample amount used for one measurement is preferably 10 to 15 g. The higher the melting temperature, the lower the viscosity of the compound, but there is naturally a limit due to the heat resistance of the organic binder used. Usually, 200 ° C or lower is desirable. After the sample is put into the cylinder, it is necessary to hold the temperature of the cylinder and the sample until the temperature is stabilized. Thereafter, a piston is inserted, a weight is placed, and a molten compound is extruded with a load. The time required for the piston to be pushed down by 25 mm from a certain position was measured, and the MFR was calculated according to the following formula. This time measurement operation is all performed automatically.

MFR (T, M, B) = (426 × L × ρ) ÷ t In this equation, T: measured temperature, M: test load, B: operation B
L: distance traveled by piston, ρ: density of compound at sample temperature, t: average time required for piston to travel length L, 426: area of piston and cylinder (cm ² ) Average value x 600 (number of seconds in 10 minutes).

On the other hand, such a zirconia powder needs to have a sintered body made of the zirconia powder having a sufficient density. Therefore, a sintered body of the obtained powder was prepared and its density was measured.

Now, the present invention will be described in further detail with reference to Examples.

[0022]

EXAMPLE 1 A zirconia sol having a zirconia conversion rate of 90% was obtained by boiling a 0.3 mol / liter solution of zirconium oxychloride (hereinafter, referred to as a raw material liquid) in a reflux state for about 200 hours. Subsequently, 5% by volume of the sol in the boiling state
Extract the part and replenish the same volume of the stock solution. This operation
Repeat every 30 minutes. As the number of repetitions increased, the zirconia conversion gradually increased and reached a steady state at about 98% conversion after about 100 repetitions. The size of the zirconia sol particles at this time was about 1000 angstroms. Under a steady state, the zirconia sol was withdrawn in the same manner, and the supply operation was repeated to collect and produce about 100 liters of zirconia sol.

Subsequently, the sol was concentrated to about 20 liters by an ultrafiltration operation. For the filtration, a cylindrical ultrafiltration membrane module was used, and dehydration and concentration were performed by circulating the sol in the membrane module. Next, a 2.5 mol / liter zirconium oxychloride solution was added to the concentrated zirconia sol so as to be 10% by weight in terms of the amount of zirconia.

Furthermore, the ratio of yttria Y ₂ O ₃ / (Y ₂ O ₃ + ZrO ₂ )
It was added so as to have a concentration of 3 mol% and stirred for a day. Yttria was completely dissolved to obtain a mixed solution having a pH of 0.5. This mixed solution was spray-dried to obtain about 8 kg of dry powder.
The dried powder was calcined at 870 ° C. for 2 hours in an air atmosphere in a tubular furnace, washed with water, pulverized for 8 hours, and dried again to prepare a partially stabilized zirconia (PSZ) powder. The BET specific surface area of the PSZ powder thus obtained was 15.4 m ² / g.

1505 g of this PSZ powder was weighed and dried at 150 ° C. for 1 hour or more to obtain 1500 g of dry powder. 3 pieces of this dry powder
Put it into a mixing tank of a kneader (Moriyama Seisakusho type MS kneader) preheated to 140 ° C with 37g of organic binder,
Kneaded. The binder softens with the start of kneading and mixes with the powder. After kneading for several minutes, turn off the heater of the kneader.
Kneading proceeds while the temperature of 40 ° C. is maintained. After kneading for one hour in this way, the compound taken out is cooled,
It was pulverized and sieved under a 0.5 mm mesh sieve.

Next, a melt indexer (manufactured by Toyo Seiki Seisaku-sho, Ltd.) weighing 13 g of the above powder and sufficiently preheating it at 150 ° C.
Into the cylinder, squeeze out the air inside, and attach the piston. As it is
The mixture was held for 3 minutes, and after the temperature of the sample, cylinder and piston reached equilibrium, a molten compound was extruded under a load of 10 kg. The subsequent measurement of the extrusion time and the calculation of the MFR are performed automatically by the apparatus. This measurement was performed three times, and the average value was adopted as the measured value. The 10% zirconium oxychloride-added zirconia powder compound thus measured
The MFR was 252 g / 10 minutes. Further, this PSZ powder was molded by a mold press to prepare a sintered body, and its density was measured.
The molding pressure is 700 kgf / cm ² and the sintering temperature is 1450 ° C. The resulting density was 6.03 (98.8% relative density).

Examples 2 to 5 PSZ powders were prepared in the same manner as in Example 1 except that the addition amounts of zirconium oxychloride were 0, 5, 8, and 20% by weight. Table 1 shows the MFR, BET specific surface area, and sintered powder density of these compounds together with Example 1.

[0028]

[Table 1]

It has been confirmed that the addition of zirconium oxychloride does not affect the BET specific surface area, but exhibits an excellent effect of improving fluidity. Also, it was confirmed that the density of the sintered body was reduced with the powder added at 20% by weight, and it was confirmed that the addition amount more than this was not desirable.

Examples 6 and 7 In Examples 1 to 5, P using ₃ mol% of Y ₂ O ₃ as a stabilizer was used.
SZ (3Y) was exemplified. In 3Y, 70-95% of the crystal phase of the powder is tetragonal. On the other hand, zirconia (0
Y) is 100% monoclinic. In order to confirm that the addition of zirconium oxychloride is effective in improving the fluidity also in 0Y, a powder obtained by adding 0% and 10% of zirconium oxychloride to 0Y powder in the same manner as in Example 1 was used. The same measurement was performed. Table 2 shows the measurement results.

[0031]

[Table 2]

It was confirmed that the addition of zirconium oxychloride was also effective for the 0Y powder.

Example 8 In a hydrolysis reaction, a hydrated zirconia sol having a zirconia addition rate of 90% was concentrated by heating under reduced pressure. Table 3 shows the measurement results of a compound prepared using the zirconia fine powder obtained by drying and calcining the concentrated sol thus obtained in the same manner as in Example 1.

[0034]

[Table 3]

Claims (4)

[Claims] 1. A method for producing zirconia fine powder, comprising drying and calcining a hydrated zirconia sol containing a zirconium salt or a mixture of a hydrated zirconia sol containing a zirconium salt and a stabilizer. 2. The zirconia fine powder according to claim 1, wherein the zirconium salt according to claim 1 is at least one zirconium salt selected from zirconium oxychloride, zirconium chloride, zirconium nitrate, and zirconium sulfate. Manufacturing method. 3. A method for producing a fine zirconia powder, characterized in that the amount of Zr contained in the zirconium salt according to claim 1 or 2 is 3% by weight or more and 30% by weight or less of the total Zr amount. 4. A zirconia fine powder obtained by the production method according to claim 1.