JPH0543308A - Method for producing translucent ceramics - Google Patents

Abstract

(57) [Summary] [Structure] The method for producing the translucent ceramics of the present invention is as follows.
After mixing polyvinyl alcohol to a mixed powder of 01 to 0.2% by weight of magnesium oxide powder, 0.01 to 0.2% by weight of yttrium oxide powder and aluminum oxide powder,
Waxes with a softening point of 50 to 90 ° C and MFR of 100 to 300 g /
A kneaded material for injection molding is prepared by adding a binder material consisting of 10 minutes of thermoplastics, and then injection molding, debinding and sintering are performed. [Effect] In a powder kneaded product for injection molding, a small amount of magnesium oxide powder and yttrium oxide powder are uniformly dispersed in the aluminum oxide powder, and as a result, a complex shaped ceramic product excellent in translucency is manufactured. It becomes possible.

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 a ceramic showing translucency in the visible light region.

[0002]

2. Description of the Related Art Generally, translucent ceramics are manufactured by press-molding ceramic powder and then sintering the powder. However, with this method, it is difficult to manufacture a product having a three-dimensionally complicated shape or a product having a thin portion. Further, in order to obtain a product having a complicated shape, the sintered body was ground by mechanical polishing after sintering. However, depending on the conditions of mechanical polishing, fine particles called hair cracks are formed on the surface of the sintered body. There is a problem that various cracks are formed, the mechanical strength and toughness of the product are remarkably reduced, and a great amount of time is required for mechanical polishing, resulting in an increase in product price. In order to eliminate the drawbacks of the conventional method, a mixture of an aluminum oxide powder, a magnesium oxide powder and a yttrium oxide powder mixed with an organic binder is injection-molded in a mold having a predetermined shape to obtain a mixture. It has been attempted to manufacture a translucent ceramic product by heating the injection-molded article to remove the binder, and then subject it to sintering treatment. According to this method, it is possible to manufacture a product having a complicated shape.

[0003]

However, in the above-mentioned method of performing the injection molding, since the organic binder is used in addition to the mixed powder of the metal oxide, the magnesium oxide powder and the yttrium oxide powder used in a small amount are used. It becomes very difficult to disperse it uniformly in the aluminum oxide powder, and the composition distribution of the resulting sintered body becomes non-uniform, and as a result, it is not possible to obtain satisfactory translucency. There's a problem.

Therefore, an object of the present invention is to provide a method capable of producing a ceramics molded article having excellent translucency and having a complicated shape.

[0005]

According to the present invention, (a) 0.
A step of preparing a mixed powder so that the composition is 01 to 0.2% by weight of magnesium oxide powder, 0.01 to 0.2% by weight of yttrium oxide powder, and the balance is aluminum oxide powder; (b) The entire mixed polyvinyl alcohol is added to the mixed powder. 1 to 10% by weight of the mixture, a step of uniformly dispersing the magnesium oxide powder and the yttrium oxide powder in the aluminum oxide powder, (c) the magnesium oxide powder and the yttrium oxide powder are uniformly dispersed To the mixed powder, a step of adding a binder material so that the total amount of the binder material and the polyvinyl alcohol is 35 to 70% by volume of the whole, and kneading, (d) the kneaded product having a predetermined shape Injection-molding step, (e) removing the polyvinyl alcohol and the binder material from the molded body, and (f) the polyvinyl alcohol and vine. The molded body from which the dur material has been removed is subjected to 1600 to 2000 in a hydrogen atmosphere or vacuum.
There is provided a method for producing a translucent ceramic, which comprises a step of sintering at ° C.

In the conventional injection molding method, since the metal oxide powders of magnesium oxide, yttrium oxide, and aluminum oxide were mixed with the binder material at the same time, a small amount of magnesium oxide and yttrium oxide were oxidized. It could not be uniformly dispersed in aluminum, and as a result, it was not possible to obtain a ceramic having excellent translucency. However, according to the present invention described above, by adding polyvinyl alcohol to the mixed powder of the metal oxide in advance, magnesium oxide and yttrium oxide are uniformly dispersed, and then a binder material is added to make injection molding and sintering. By carrying out the steps, it becomes possible to obtain the ceramics excellent in translucency.

Step (a); In the present invention, a mixed powder of magnesium oxide, yttrium oxide and aluminum oxide is first prepared, and this mixed powder is used as a starting material. The composition of this mixed powder is magnesium oxide powder.
0.01-0.2 wt% and 0.01-yttrium oxide powder
It is 0.2% by weight, and it is important to use the balance of aluminum oxide powder.When the composition is out of this range,
Satisfactory translucency cannot be obtained. That is, in order to exhibit translucency, it is necessary to set the relative density of the sintered body obtained by sintering described below to at least 99%. Magnesium oxide suppresses the growth of crystal grains in the final stage of sintering, thereby promoting the disappearance of pores inside the grain boundaries and improving the sintering density, and also makes the grain sizes uniform. Act on. Therefore, magnesium oxide plays a major role in improving the translucency. For example, when the content of magnesium oxide is less than 0.01% by weight, it is insufficient to exert such an effect, the density of the sintered body does not become sufficiently high, and a satisfactory translucency cannot be obtained. On the other hand, if it is more than 0.2% by weight, magnesium oxide or a composite oxide of this and other metal oxides is formed at the crystal grain boundaries of the sintered body, which causes light scattering and lowers the translucency. Will cause inconvenience. Further, yttrium oxide has a function of significantly increasing the effect of magnesium oxide as a sintering aid, but its content is 0.01
If the amount is less than wt%, such effects will not be sufficiently exhibited,
The density of the sintered body is not sufficiently high, and for example, it is not possible to obtain translucency with an in-line transmittance of 70% or more. Also
If the amount is more than 0.2% by weight, the grain boundary of the sintered body,
Yttrium oxide or a composite oxide of yttrium oxide and another metal oxide is formed, which causes a decrease in translucency as described above.

In the present invention, each metal oxide powder used for preparing this mixed powder may be a commercially available powder, but in order to exhibit translucency,
It is preferable to use a high purity one. In addition, in order to improve the sintered density and to express good translucency,
Their average particle size is on the order of submicrons, e.g.
It is desirable to be in the range of 8 μm or less.

Step (b); In the present invention, next, polyvinyl alcohol is mixed with the mixed powder. This polyvinyl alcohol has a surfactant-like action, and by using this, the magnesium oxide powder and the yttrium oxide powder are uniformly dispersed in the aluminum oxide powder.

The polyvinyl alcohol is used in a proportion of 1 to 10% by weight, in particular 2 to 6% by weight, based on the total mixture obtained. The amount of polyvinyl alcohol used is 1% by weight
When the amount is less than 10% or more than 10% by weight, magnesium oxide and yttrium oxide are not uniformly dispersed, and as a result, the translucency of the final product (sintered body) varies depending on the portion.

As this polyvinyl alcohol,
Those having an average degree of polymerization of 500 to 2500 and an average degree of saponification of 66% or more are preferably used. Mixing of this polyvinyl alcohol and the mixture prepared in step (a) can be carried out by various methods known per se, but the method of producing granular powder by a spray dryer often used in fine ceramics is the most preferable. It is suitable.

Step (c); in this step (c),
Kneading is performed by adding a binder material to the mixed powder in which the magnesium oxide and the yttrium oxide obtained in (b) are uniformly dispersed. The binder material used in this step is used to effectively carry out the injection molding described later, and is usually made of a thermoplastic that contributes to the shape retention of the molded body after injection molding and the flow during injection molding. Used in combination with thermoplastics that contribute to the sex.

The thermoplastics that contribute to shape retention include melt flow rate (MFR, ASTM D 123
6, 230 ° C.) is a thermoplastic resin having a range of 100 to 300 g / 10 minutes, for example, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, polystyrene and the like. .. MFR
If it is less than 100 g / 10 min, the injection moldability becomes unsatisfactory, and if it is more than 300 g / 10 min, the strength and shape retention of the injection molded product will be poor.

As a thermoplastic that contributes to fluidity during injection molding, the Vicat softening point (JIS K 720
6) in the range of 50 to 90 ° C., for example, waxes such as paraffin wax, microcrystalline wax, low molecular weight polyethylene wax, modified wax and atactic polypropylene. When the softening point is lower than 50 ° C., the cycle time of injection molding becomes long, and the softening point is likely to cause softening, resulting in inferior workability during molding. Further, when the softening point is higher than 90 ° C., the fluidity is lowered, and the thermal decomposition point is increased, so that the debinding property is lowered.

The thermoplastics that contribute to shape retention and the thermoplastics that contribute to fluidity at the time of injection molding are generally 4: 1 to 1: 4 by weight, especially, depending on the type. It is preferred to use it in a ratio of 3: 1 to 1: 3.

In the present invention, it is necessary that the above-mentioned binder material is used in a total amount of 35 to 70% by volume based on the kneaded material in the total amount with the above-mentioned polyvinyl alcohol. If it is less than 35% by volume, the fluidity of the kneaded product will be reduced, making injection molding difficult, and if it is more than 70% by volume, debinding will be very difficult and the transparency of the final product will decrease. It causes inconvenience. The kneading with the binder material can be easily performed using a kneading device such as a kneader or various mixers.

Step (d); Next, the kneaded material prepared in the step (c) is injected into a mold having a desired mold to obtain a molded product having a target mold. This injection molding can be carried out by directly using the equipment and devices used in ordinary plastic injection molding. Generally, it is desirable that the injection conditions are a heating temperature of 80 to ²⁰⁰ ° C. and an injection pressure of 500 to 2000 kg / cm ² .

Step (e); Next, the binder is removed from the molded body to remove the polyvinyl alcohol and the binder material contained in the molded body. This debinding is usually performed by heating in the air or an inert atmosphere such as nitrogen gas. Heating temperature is generally 400
It is in the range of ~ 600 ° C.

Step (f): Following the above debinding, a sintering process is performed. In the present invention, it is necessary to carry out this sintering in a hydrogen atmosphere or in a vacuum. Generally, in the final stage of sintering, small pores are usually present in the crystal grains, and eliminating these pores is important for improving the light-transmitting property. That is, when sintering is performed in hydrogen, hydrogen will remain in the pores, but since hydrogen has excellent diffusivity, it is easy to pass through the grain boundaries and pass through the sintered body. Discharged from. As a result, the pores easily disappear due to ion diffusion.
Further, since there is almost no gas in the pores in a vacuum, the pores are similarly easily extinguished by the diffusion of ions. Therefore, ceramics having excellent translucency can be obtained by sintering in a hydrogen atmosphere or in a vacuum.

The sintering temperature is 1600 to 2000 ° C., especially 1700 to
The range is 1850 ℃. At a temperature lower than 1600 ° C, the relative density of the obtained sintered body does not sufficiently improve, and as a result, the translucency is lowered, and when sintering is performed at a temperature higher than 2000 ° C, the sintered body Magnesium evaporates from the surface, and as a result, the relative density on the surface of the sintered body is not improved, and the sintered body becomes white without being translucent. Such sintering is performed to such an extent that the relative density of the sintered body becomes 99% or more.

The ceramics thus obtained contain 0.01 to 0.2% by weight of magnesium oxide and yttrium oxide.
Since it has a composition of 0.01 to 0.2% by weight and the balance of aluminum oxide, it has extremely excellent translucency in the visible light region. For example, as is clear from the examples described below,
The in-line transmittance is in the range of 70% or more.
This in-line transmittance indicates the ratio of the intensity of transmitted light that is incident within a certain angle to the intensity of incident light when parallel rays of constant intensity are incident on a sample having a certain thickness.

[0022]

Example 1 Magnesium oxide powder having an average particle size of 0.15 μm, yttrium oxide powder having an average particle size of 0.15 μm, and an average particle size of 0.15 μm.
A mixed powder having a magnesium oxide content of 0.05% by weight and a yttrium oxide content of 0.05% by weight was prepared using 53 μm of aluminum oxide powder. Next, as shown in Table 1, polyvinyl alcohol (average degree of polymerization: 1700, average degree of saponification: 88%) was added to the above-mentioned mixed powder with various addition amounts, and granulated using a centrifugal spray dryer. Turned into
A uniform dispersion was prepared. Prepared uniform dispersion (granule)
The median particle size of each is approximately 50 μm. To each of these uniform dispersions, various thermoplastics were added as a binder material, and a kneaded product was prepared with a planetary mixer. The types of thermoplastics used and their addition amounts are as shown in Table 1. The volume% of the total amount of this thermoplastic and polyvinyl alcohol is also shown in Table 1. This kneaded product was injection molded with an injection molding machine under the conditions of an injection temperature of 90 ° C. and an injection pressure of 600 kg / cm ² to obtain a disk-shaped molded product having a diameter of 10 mm and a thickness of 2 mm. Then, the molded body was debindered in an air stream while heating (heating temperature: 500 ° C.), and further sintered in a hydrogen stream at a temperature of 1800 ° C. for 6 hours. The surface of the obtained sintered body was polished with diamond to a thickness of 1 mm, and then the visible light region (300 nm to 1100 n
In-line transmittance was measured in m). The measurement results are shown in Table 1.

Examples 2 to 6 The magnesium oxide content and the yttrium oxide content in the mixed powder of metal oxides were variously changed as shown in Table 1, and the kind and blending amount of the thermoplastics used were changed as shown in Table 1. A disk-shaped injection-molded article was prepared in the same manner as in Example 1 except that the above was carried out. Further, a sintered body was prepared in the same manner as in Example 1 except that the sintering was performed in a hydrogen stream. Table 1 shows the in-line transmittance of the obtained sintered body.

Comparative Examples 1 to 6 For comparison, the above Examples 2 to 6 were used, except that the amounts of the magnesium oxide powder, the yttrium oxide powder, the polyvinyl alcohol, and the thermoplastic as the binder material were changed variously. A sintered body was prepared in the same manner, and its in-line transmittance was measured. The measurement results are shown in Table 2. In Comparative Examples 1 to 3, the amounts of magnesium oxide and yttrium oxide used are outside the range of the present invention, and in Comparative Example 4, the amounts of polyvinyl alcohol used are outside the range of the present invention. Is an example in which the total amount of the polyvinyl alcohol and the thermoplastic compound is outside the range of the present invention.

[0025]

[Table 1]

[0026]

[Table 2]

In the above table, the amounts of the polyvinyl alcohol and the binder material added are shown in weight% of the mixture obtained by adding the components.

[0028]

According to the manufacturing method of the present invention, it is possible to effectively manufacture a ceramic molded article having a three-dimensionally complicated shape and excellent translucency by using the injection molding method. Becomes

Claims (1)

[Claims] 1. A step of: (a) preparing a mixed powder so that the composition is 0.01 to 0.2% by weight of magnesium oxide powder, 0.01 to 0.2% by weight of yttrium oxide powder, and the balance is aluminum oxide powder; Add 1 part of polyvinyl alcohol to the mixed powder.
~ 10 wt%, a step of uniformly dispersing magnesium oxide powder and yttrium oxide powder in aluminum oxide powder, (c) the mixed powder in which magnesium oxide powder and yttrium oxide powder are uniformly dispersed A step of adding a binder material so that the total amount of the binder material and the polyvinyl alcohol is 35 to 70% by volume of the whole and kneading, (d) injecting the kneaded product into a molded article of a predetermined shape. A step of molding, (e) a step of removing the polyvinyl alcohol and the binder material from the molded body, and (f) a molded body from which the polyvinyl alcohol and the binder material have been removed, in a hydrogen atmosphere or a vacuum, 16
A method for producing a translucent ceramic, which comprises a step of sintering at 00 to 2000 ° C.