JP2011073907A - Sintered body of zirconia and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered body of zirconia particularly suitable for a dental material because of excellence in strength, translucency and resistance to hydrothermal degradation. <P>SOLUTION: There is provided the sintered body of zirconia including yttria of 3-5.5 mol% characterized in that (1) the apparent porosity is 1% or lower, (2) the number of pores having a pore diameter of 10 μm or larger is 30 or less in an area of 2 mm×2 mm of a sample flake of 0.2 mm in thickness, and (3) the mean crystal-particle diameter is 0.2-1 μm. A method for manufacturing the same is also provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a zirconia sintered body and a method for producing the same. More specifically, the present invention relates to a zirconia sintered body suitable for dental materials such as dentures and orthodontic brackets and a method for producing the same.

Since a zirconia sintered body (hereinafter abbreviated as “Y-TZP”) in which a small amount of Y ₂ O ₃ is dissolved as a stabilizer is high in strength and toughness, cutting tools, dies, nozzles, bearinge, etc. In addition to structural materials, they are widely used as biomaterials such as dental materials. In particular, when used as a dental material, not only mechanical properties such as high strength and high toughness but also optical properties such as translucency and color tone are required from an aesthetic point of view.

Studies and research focusing on only the mechanical property of increasing the strength of Y-TZP have been made. The high-strength mechanism in Y-TZP is due to the fact that the tetragonal phase zirconia contained in the sintered body undergoes a martensitic transition to the monoclinic phase due to stress. In ordinary pressure sintering of Y-TZP having a Y ₂ O ₃ concentration of 2 to 3 mol%, coarse pores remain in the sintered body, and the fracture strength of the sintered body is the size of the coarse air hole. The three-point bending strength of the atmospheric sintered body in which the rough atmospheric pores remain is about 1200 MPa. Moreover, since the sintered compact in such a composition area | region has almost no translucency, it cannot utilize for a dental use. In order to forcibly exclude such pores, studies have been made on high strength and translucency using a hot isostatic press (hereinafter abbreviated as “HIP”) or a hot press. Not only is it insufficient in terms of performance, but there is a problem inherent to the high pressure sintering method, that is, a problem of cost, and it is in a situation where it cannot be practically used. In the hot press method, there is a drawback that the green compact processed by CAD-CAM cannot be sintered, so that it cannot be practically used for dental use. Further, in the region where the mechanical strength peak Y ₂ O ₃ content is 2 to 3 mol%, hydrothermal degradation (strength accompanying phase transition from tetragonal to monoclinic when heat-treated in high-temperature saturated steam is used. Deterioration: see Non-Patent Document 1), and there are no reports on zirconia sintered bodies that can satisfy the three conditions of mechanical strength, hydrothermal deterioration resistance and translucency.

  In Non-Patent Document 2, the three-point bending strength of a zirconia sintered body having an yttria concentration of 2 to 3 mol% produced by the HIP pressure sintering method is higher than that of a normal pressure sintered body. However, although the maximum strength is about 1700 MPa or higher than that value, it is a normal HIP treatment, and the translucency is not sufficient.

According to Patent Document 1, a primary sintered body having a yttria concentration of 2 to 4 mol% zirconia (relative density of 95% or more) is prepared, and then subjected to HIP treatment at a pressure of 50 MPa or more and 1200 to 1600 ° C. Thus, a zirconia sintered body having a high strength of 1700 MPa or more and a predetermined translucency has been reported. However, as far as the examples are concerned, either the temperature of the primary sintering or the HIP treatment exceeds 1400 ° C., and the Y ₂ O ₃ concentration of the produced zirconia sintered body is limited to 2 to 3 mol%. Yes. In such a composition region and temperature conditions, hydrothermal deterioration easily occurs, and it is difficult to put to practical use.

  In Patent Documents 2 to 4, a composite sintered body of zirconia having a yttria concentration of 2 to 4 mol% and an oxide such as alumina produced by a pressure sintering method such as HIP exhibits a high strength of 2000 MPa or more. Is disclosed. However, alumina has a structure that is dispersed and precipitated in the zirconia sintered body. Considering that the dispersed alumina is significantly different from the refractive index of zirconia and that the alumina belongs to a hexagonal crystal structure. For example, it is difficult to obtain translucency with the ceramics. As a comparative example, yttria concentration 2 to 4 mol% zirconia containing no oxide such as alumina is shown. However, as in the case of Non-Patent Document 1, almost no translucency is recognized in principle.

  Patent Document 5 discloses that, similarly to Patent Documents 2 to 4, a composite sintered body of yttria concentration 2 to 4 mol% zirconia and alumina exhibits a high strength of 2000 MPa or more. As a comparative example, although the maximum average strength 1854 MPa is described as the strength of yttria concentration 2 to 4 mol% zirconia not containing oxide such as alumina, the translucency is not sufficient as in Non-Patent Document 1. .

  In order to obtain a sintered body having translucency and color tone, there is a method in which a sintered body blackened with HIP in an argon atmosphere is heated and oxidized in the air (Non-Patent Document 3). However, when reoxidized, there is a problem that the strength of the sintered body decreases.

On the other hand, orthodontic brackets made of zirconia including yttria are disclosed as having a certain degree of translucency (Patent Documents 6 to 8). In any case, HIP in an oxygen mixed gas atmosphere is used and the strength is 1620 MPa or less, but it is still insufficient in terms of translucency. Moreover, although the method aiming to make high mechanical strength and translucency compatible is disclosed by patent document 1 and patent document 9, it is a precondition that HIP processing is performed, and the obtained zirconia sintering was carried out. The total light transmittance in the body (0.5 mm) is about 40 to 50% (generally, the total light transmittance is detected from the vertical direction of the sample because all the light quantity that can propagate inside the material is detected using an integrating sphere. The typical transmittance for measuring incident light and measuring only the light with high linearity is more severe.) An example in which the transmittance (linear transmittance) is described in a part of the prior literature is found, but it is about 7 to 12% in a sample having the same thickness (0.5 mm). The optical transmission loss can be calculated from the following equation.
α = (1 / L) x 10 log (P ₀ / P _i ) Equation (1)
(Where α: optical transmission loss, L (sample length), P ₀ (incident power), P _i (output power)))

  As a result of calculation based on the above formula, the α value of the prior document is a numerical value of 23 to 18 / mm. This value can be judged to be very inferior to that of the zirconia sintered body not using the HIP of the present invention described later.

  Thus, Y-TZP having both high strength and translucency and color tone from an aesthetic point of view has not been obtained. In particular, mechanical strength, translucency, and hydrothermal deterioration can be satisfied without compounding oxides such as alumina with yttria concentration of 2 to 4 mol% zirconia to 1 wt% or more, substantially 10 wt% or more. A sintered body has not been obtained.

  In particular, there are currently no special legal restrictions on dental materials, but since zirconia sintered bodies are always exposed to water and body temperature because they are used in the mouth, it is necessary to assume characteristic deterioration during long-term use. is there. Further, it is known that a zirconia sintered body undergoes strength deterioration when treated in high-temperature saturated steam. For this reason, in view of the problems inherent in the zirconia sintered body and the usage environment of the dental material, it is necessary to develop a zirconia sintered body having hydrothermal degradation resistance. In recent years, a dental material has appeared as an application of Y-TZP, and has been studied or used as a denture material, an orthodontic bracket or the like. As one of the denture production methods, there is a method of processing a sintered body into a desired shape by a CAD-CAM system, and this sintered body is called a mill blank. As described above, although this sintered body is required to have high strength enough to withstand the meshing of teeth and light transmission (transparency) close to natural teeth as aesthetics, Y-TZP currently used is It is a white sintered body having a strength of about 1200 MPa and hardly transmitting light, or a sintered body having very low translucency. In this respect, as a mill blank, in addition to high strength and translucency, it is necessary to improve the hydrothermal deterioration resistance as described above. In particular, as orthodontic brackets for dental materials, it is desired to develop a sintered body having higher strength and translucency and excellent hydrothermal deterioration resistance.

JP 2008-50247 A JP 60-86073 A JP-A-60-226457 JP 60-235762 A Japanese Patent Laid-Open No. 3-80153 Japanese Patent Laid-Open No. 3-170148 Japanese Patent Application Laid-Open No. 08-117248 Japanese Patent Laid-Open No. 11-276504 JP 2008-222450 A

Isao Yamashita and Koji Tsukuma, “Phase Separation and Hydrothermal Degradation in 3mol% Y2O3-ZrO2 Ceramics”, Journal of the Ceramic Society of Japan, vol.113, pp530-33 (2005) .- 43 (1986) Ceramics Bulletin Vol. 64, 310 (1985) Zirconia Ceramics 8, Shigeyuki Somiya, Masahiro Yoshimura, Uchida Otsuru, 33-43 (1986)

  Therefore, the main object of the present invention is to provide a zirconia sintered body particularly suitable for a dental material because it has excellent strength, translucency and hydrothermal deterioration resistance.

  As a result of intensive studies in view of the problems of the prior art, the present inventor has found that the above object can be achieved by employing a specific composition and a specific manufacturing method, and has completed the present invention.

That is, this invention relates to the following zirconia sintered compact and its manufacturing method.
1. A zirconia sintered body containing 3 to 5.5 mol% of yttria, (1) apparent porosity is 1% or less, and (2) in an area of 2 mm × 2 mm in a thin piece sample having a thickness of 0.2 mm The zirconia sintered body is characterized in that the number of pores having a pore diameter of 10 μm or more is 30 or less, and (3) the average crystal grain size is 0.2 to 1.5 μm.
2. Item 2. The zirconia sintered body according to Item 1, wherein the transmittance in the wavelength range of 400 to 700 nm at a sample thickness of 3.0 mm is 7% or more.
3. Item 3. The zirconia sintered body according to Item 1 or 2, wherein the three-point bending strength is 800 to 1500 MPa.
4). The crystal phase is (1) tetragonal fluorite crystal phase 40 to 100% by volume containing 3 mol% or less yttria and (2) cubic fluorite crystal phase 0 to 5 mol% or more yttria Item 4. The zirconia sintered body according to any one of Items 1 to 3, comprising 60% by volume.
5). The ratio of (strongest peak of monoclinic phase) / (strongest peak of tetragonal phase) in powder X-ray diffraction after hydrothermal treatment of the zirconia sintered body at 180 ° C. for 5 hours is 1 or less, Item 5. The zirconia sintered body according to any one of Items 1 to 4.
6). Item 6. The zirconia sintered body according to any one of Items 1 to 5, which contains at least one of an aluminum component and a magnesium component in a range of 0.5% by weight in terms of oxide.
7). A dental material comprising the zirconia sintered body according to any one of Items 1 to 6.
8). An orthodontic bracket including the zirconia sintered body according to any one of Items 1 to 6.
9. A method for producing a zirconia sintered body containing yttria,
(1) First to obtain a green compact by molding a raw material powder containing yttrium and zirconium and having an average primary particle diameter of 10 to 100 nm and a BET specific surface area of 3 to 30 m ² / g or a granulated product thereof. Process,
(2) Zirconia sintering including a second step in which the green compact is fired at 1300 to 1600 ° C. under atmospheric pressure in a vacuum atmosphere of 10 ¹ to 10 ⁻⁴ Pa or in an oxygen-containing atmosphere with an oxygen concentration of 50% or more. Body manufacturing method.
10. Item 10. The method according to Item 9, wherein the raw material powder is zirconia powder containing 3 to 5.5 mol% yttria as a stabilizer, and the purity thereof is 99% or more.
11. The green compact has (1) an average pore diameter of 0.02 to 0.3 μm, (2) a maximum pore diameter of 10 μm or less, and (3) a volume occupied by pores having a pore diameter of 5 μm or more with respect to the total pore volume. Item 11. The method according to Item 9 or 10, wherein the ratio is 5% or less.
12 Item 12. The method according to any one of Items 9 to 11, wherein the raw material powder further contains at least one of aluminum oxide and magnesium oxide within a range of 0.5% by weight.
13. The zirconia sintered compact obtained by the manufacturing method in any one of said item 9-12.

  The zirconia sintered body of the present invention is excellent in both strength, translucency and hydrothermal deterioration resistance, and therefore can be used for a wide range of applications, mainly for applications requiring these characteristics, including dental materials. . Moreover, according to the manufacturing method of the present invention, since the predetermined green compact is fired in a specific firing atmosphere, the number of residual pores can be reduced to the limit without requiring treatment under high pressure such as HIP. Can do. As a result, a zirconia sintered body having high strength, translucency and hydrothermal deterioration resistance as described above can be obtained.

  In particular, in the present invention, when the pore size distribution in the green compact is precisely controlled, a desired zirconia sintered body can be produced by more effectively reducing the residual pores. Incidentally, in the production of a zirconia sintered body using a general HIP process, defects such as pores can be reduced by applying a forced pressure by HIP, so that it is not necessary to control the structure of the sintered body before the HIP process.

Furthermore, although the sintering temperature of the present invention is in the range of 1300 to 1600 ° C., a general partially stabilized zirconia sintered body may cause significant hydrothermal deterioration when sintered at a temperature of 1350 ° C. or higher. (Kyoto Nakayama et al., “Thermal Stability of Y-TZP with Yttria Stabilized Zirconia-1-B ₂ O ₃ —Al ₂ O ₃ —SiO ₂ ”, Shinagawa Technical Report, (38) pp43- 48 (1995/03)). However, the zirconia sintered body obtained by the process of the present invention has a monoclinic / tetragonal diffraction peak ratio of 1 in the X-ray diffraction pattern even when autoclaving in saturated steam at 180 ° C. for 5 hours. .00 or less. As a result, the present invention can provide an excellent zirconia sintered body having a strength change accompanying the hydrothermal deterioration (strength after hydrothermal treatment / strength immediately after sintering) of 0.80 or more. Incidentally, although it is easy to obtain high strength with a yttria 2-3 mol% added zirconia sintered body that is widely used, extreme strength deterioration or material when autoclaved under the conditions described in the present invention or more severe conditions. As a result, the problem remains in terms of long-term use of materials.

  Further, in a zirconia sintered body, translucency can be obtained by HIP treatment at the temperature described in Patent Document 8, but such translucency cannot be said to be sufficient. The zirconia sintered body obtained in the present invention (vacuum or atmospheric pressure sintering) exhibits a light-transmitting property superior to that of zirconia treated with HIP. Regarding the α value described in the above formula (1), the zirconia sintered body is prepared using HIP in the prior patent, but the surface reflection loss of zirconia (which differs slightly depending on the composition, but the refractive index n = 2). .2, the value reaches 23-18 even considering that there is a reflection loss of 14.1% on one side and 28.2% on both sides). In the present invention, the transmittance was measured with a sample thickness of 3 mm, but the α value was about 3.8 to 2.7, indicating a light transmission property superior to that of the HIP method.

In the present invention, the pore size distribution in the green compact obtained by the CIP treatment is shown. The present invention and the conventional art 3.3 mol% was prepared in Y ₂ O ₃ doped zirconia sintered body (thickness 200μm thin sample) result of observation with a transmission electron microscope showing a (photograph). FIG. 3 shows a state (appearance) when a white LED is irradiated to the product of the present invention and the conventional product. It is the schematic of the sintering apparatus suitable for producing the translucent zirconia sintered compact of this invention. It is the schematic of the sintering apparatus suitable for producing the translucent zirconia sintered compact of this invention. It is the schematic of the sintering apparatus suitable for producing the translucent zirconia sintered compact of this invention.

DESCRIPTION OF SYMBOLS 1 Heater 2 Rotary pump 3 Flowmeter 4 Gas cylinder 5 Sample stand 6 Sample 7 Heat insulating material 8 Flange 9 Firing furnace 10 Turbo molecular pump 11 Vacuum chamber 12 Piping 13 Valve

1. Zirconia sintered body The zirconia sintered body of the present invention is a zirconia sintered body containing 3 to 5.5 mol% of yttria, (1) apparent porosity is 1% or less, and (2) thickness. A 0.2 mm thin piece sample has 30 or less pores having a pore diameter of 10 μm or more in an area of 2 mm × 2 mm, and (3) an average crystal grain size is 0.2 to 1.5 μm.

  The zirconia sintered body of the present invention is limited to those containing 3 to 5.5 mol% yttria. Yttria is basically present as a stabilizer in a solid solution in the zirconia sintered body. By setting the yttria content to 3 to 5.5 mol%, more preferably 3 to 5 mol%, excellent strength, translucency, and hydrothermal deterioration resistance can be exhibited. Zirconia sintered bodies with this composition range are used as general structural materials because the mechanical strength peaks in the range of 2 to 3 mol% of the stabilizer, but zirconia sintered with sufficient optical properties. There is a technical problem that it is difficult to produce a body. Further, when the yttria content is less than 3 mol%, there is a problem of hydrothermal deterioration, and the strength may be deteriorated when the zirconia sintered body is used for a long time in high humidity or water. On the other hand, it has been reported that when the yttria content exceeds 3 mol%, an extreme decrease in strength occurs. However, it is understood that the physical properties of the substance (composition) are unique, and there are no reports on the improvement of its strength properties. It is in. On the other hand, in the present invention, even if the yttria concentration is 3 mol% or more, the conventional concept is achieved by reducing the size and amount of the structural defects (mainly residual pores) existing inside the sintered body material. Not only does it achieve high strength, it also has a major feature in that it has greatly improved translucency and hydrothermal resistance.

  In the zirconia sintered body of the present invention, other components may be contained within a range not impairing the effects of the present invention. For example, in order to color a zirconia sintered compact, you may contain at least 1 sort (s), such as a transition element and rare earth elements, in 1000 ppm or less. Further, in order to further increase the strength, aluminum alone or a combination of aluminum and magnesium may be contained in an amount of 0.5% by weight or less in terms of oxide.

  The apparent porosity of the zirconia sintered body of the present invention is 1% or less, preferably 0.5% or less. When the apparent porosity exceeds 1%, predetermined mechanical strength, translucency, etc. may not be obtained. The transmission characteristics are closely related to the structure defects existing inside the material, particularly the residual pore volume having the largest refractive index difference from the base material zirconia. The smaller the amount of pores remaining in the sintered body with theoretically good translucency, the higher the transmittance and mechanical strength, so the residual pore volume in the zirconia sintered body that can be produced by the present invention is the prior application. It is considered to be equivalent to or less than that produced by the patented HIP method.

  The zirconia sintered body of the present invention has 30 or less, preferably 10 or less pores having a pore diameter of 10 μm or more in an area of 2 mm × 2 mm in a thin piece sample having a thickness of 0.2 mm. When the number of pores having a pore diameter of 10 μm or more exceeds 30 in an area of 2 mm × 2 mm, it becomes difficult to obtain a zirconia sintered body having both predetermined mechanical strength and translucency.

  The average crystal grain size of the zirconia sintered body of the present invention is 0.2 to 1.5 μm, preferably 0.2 to 0.5 μm. By defining within this range, it is possible to obtain translucency as well as excellent mechanical strength. In the zirconia sintered body of the present invention, sufficient strength is maintained even in the range of an average crystal grain size of 0.2 to 1.5 μm by defining the porosity and the number of pores having a pore diameter of 10 μm or more as described above. Not only can this be done, but it is also possible to increase translucency by reducing tissue defects.

  The zirconia sintered body of the present invention is a polycrystalline body. As the crystal phase, (1) a tetragonal fluorite-type crystal phase containing 3 mol% or less yttria and 40 to 100 vol% and (2) a cubic fluorite-type crystal phase containing 5 mol% or more yttria It is preferable to contain 0-60 volume%. The high-strength mechanism of zirconia is due to the phase transition from the tetragonal fluorite-type crystal phase to the monoclinic system due to the application of stress. Therefore, in order to increase the strength, the tetragonal fluorite of (1) above is used. It is preferable that a predetermined amount of the mold crystal phase is present. In particular, the zirconia sintered body of the present invention includes substantially (1) 40 to 100% by volume of a tetragonal fluorite crystal phase containing 3 mol% or less yttria and (2) containing 5 mol% or more yttria. More preferably, the cubic fluorite-type crystal phase consists of 0 to 60% by volume. That is, it is more desirable that the zirconia sintered body of the present invention substantially consists of the crystal phases (1) and (2).

  In the present invention, since the color tone of zirconia is inherently white, an impurity such as Fe and Ni is added within a range of several thousand weight ppm or less as necessary to change the color to ivory or other colors. Is possible. Furthermore, the color tone can be freely adjusted by adding an appropriate amount of other transition gold elements or rare earth elements.

  The zirconia sintered body of the present invention is excellent in translucency. More specifically, the transmittance in the wavelength range of 400 to 700 nm at a sample thickness of 3.0 mm is 7% or more, particularly 10% or more. The upper limit of the transmittance is not particularly limited. However, when the transmittance is usually 7 to 15%, a light-transmitting property close to that of natural teeth is obtained, so that more preferable aesthetics can be obtained. This is because the light-transmitting feeling of the zirconia sintered body in the above range is very close to that of natural teeth.

In the present invention, a vertically transmitted light beam (400 to 700 nm (peak 570 nm) light, a light beam width is a circle with a diameter of 1 mm) is irradiated, and the ratio of the sample without a sample is expressed in log (logarithm). The optical density was D, and the transmittance was calculated from 1 ÷ 10 ^D × 100. This is because the conventional total light transmittance shows the transmittance of the light source (lamp) with respect to all wavelengths from ultraviolet to infrared, and there is a part that is not suitable for the dental use of the present invention. That is, since it is considered most preferable that aesthetics can be determined by visible light that can be sensed by human eyes, a method of measuring with white light in the visible wavelength range is adopted.

  The zirconia sintered body of the present invention has a three-point bending strength of 800 to 1500 MPa, preferably 950 to 1500 MPa. By having such strength, it can be suitably used as a dental material or the like.

  The zirconia sintered body of the present invention is excellent in hot water resistance. As mentioned above, there are no specific legal restrictions at present for dental materials, but since the zirconia sintered body is always exposed to water and body temperature because it is used in the oral cavity, it deteriorates the characteristics during long-term use. It is necessary to assume. Although there is no specific evaluation standard for hot water deterioration, in the present invention, a zirconia sintered body (particularly, a zirconia sintered body immediately after production) is treated with water at 180 ° C. for 5 hours for the purpose of performing this evaluation (acceleration test). Evaluation was carried out based on the ratio of (strongest peak of monoclinic phase) / (strongest peak of tetragonal phase) in powder X-ray diffraction after heat treatment. Of course, if there is no change in the mineral phase before and after hydrothermal treatment, there will be no change in strength, but the ratio of (strongest peak of monoclinic phase) / (strongest peak of tetragonal phase) is 1 or less, preferably If it is 0.8 or less, it is considered that there is virtually no problem (because this value is 1 or more, the strength is significantly reduced), and this value was used as a reference value.

  Next, the use of the sintered body of the present invention will be described. The zirconia sintered body of the present invention can be suitably used as a dental material. In particular, it is optimal as a material requiring translucency. More specifically, all ceramic crowns (bridges), porcelain laminate veneers, adhesive bridges, crown materials such as inlays and onlays, as well as orthodontic bracket bodies and parts used therefor, implant materials, etc. Can do.

Typical examples of aesthetic dental restorations include metal-baked porcelain. However, there are problems such as metal allergy problems, and the gingiva portion is darkened due to the metal color and the aesthetics are deteriorated. In recent years, all-ceramic crowns (bridges) that use alumina or zirconia, which is a high-strength, white or pale yellow ceramic instead of metal, as the core material, and are baked with transparent glass ceramic (Porcelain) on top of it. Is spreading. The spread of this method is greatly related to the fact that a method for producing a prosthesis using zirconia using a CAD-CAM system has been developed and put into practical use. As a manufacturing method, a prosthetic skeleton shape is taken into a CAD, the information is transmitted to a milling (CAM) unit, and a mill blank made of zirconia is automatically processed to create a precise shape. In such a system, a green compact that has not been fired or a calcined mill blank was used, and a sintered blank processed with a calculated size of sintering shrinkage and a mill blank subjected to HIP treatment It is known that the sintered body itself is used for processing. Since the core ceramic of an esthetic dental restoration has lower toughness than metal, it is required to be thicker by 0.1 to 0.3 mm than metal. In that case, the reflection of alumina or zirconia may hinder the transparency of the entire crown, and the desired aesthetics may not be obtained. Therefore, a zirconia sintered body having high translucency is required. Conventionally, a zirconia atmospheric pressure sintered body containing 3 mol% Y ₂ O ₃ has been used, and the transmittance is extremely low even when the strength is 900 to 1300 MPa and the thickness is thin. On the other hand, there is a technique of HIP processing the sintered body as one means for improving the strength and translucency, and the strength is 1500 to 1850 MPa and the transmittance is about 40% with a sintered body having a thickness of 0.5 mm. be able to. The strength of the zirconia sintered body prepared in this composition range can be increased, but the total light transmittance is limited to about 40%, and the hydrothermal deterioration resistance is insufficient. HIP treatment can increase the transmittance compared with atmospheric pressure sintering method, but the HIP equipment itself is expensive and the manufacturing man-hours for HIP treatment are increased, and the strength of the product after HIP treatment is high. Therefore, there are disadvantages such as subsequent processing takes a lot of time and cost. Therefore, in the manufacture of a dental prosthesis, which is a made-to-order product, when trying to use a zirconia sintered body that has been subjected to HIP processing, a large number of sintered body blocks are produced at one time (because of the high HIP processing cost). HIP processing. It is not easy to process a HIP-processed block into a tooth shape, and the processing cost becomes very expensive, so that it is difficult to use in practice. Moreover, if the green compact is calcined after CAD-CAM and then fired, then the processing cost will be reduced if HIP treatment is performed, but even in small quantities in the industry where quick delivery is required from the viewpoint of early treatment for patients, HIP In this case, the problem of HIP cost remains. In addition, the conventional zirconia sintered body treated with HIP has better translucency than non-HIP zirconia sintered body, but there is a fundamental reason that it does not reach aesthetics that can fully satisfy user needs. There is a reality that has not been made.

  On the other hand, the sintered body of the present invention not only can obtain translucency without performing HIP treatment, but also has a problem of strength reduction (insufficient) of the conventional atmospheric pressure sintering method, and further has hydrothermal resistance. Since the problem of degradability can be solved, it is optimal as various dental materials as described above, and can greatly contribute to the popularization of zirconia sintered bodies in the field of dental materials by achieving both performance and economy.

2. Method for Producing Zirconia Sintered Body The zirconia sintered body of the present invention can be suitably obtained particularly by the following production method. That is, a method for producing a zirconia sintered body containing yttria,
(1) First to obtain a green compact by molding a raw material powder containing yttrium and zirconium and having an average primary particle diameter of 10 to 100 nm and a BET specific surface area of 3 to 30 m ² / g or a granulated product thereof. Process,
(2) Zirconia sintering including a second step in which the green compact is fired at 1300 to 1600 ° C. under atmospheric pressure in a vacuum atmosphere of 10 ¹ to 10 ⁻⁴ Pa or in an oxygen-containing atmosphere with an oxygen concentration of 50% or more. It can manufacture suitably with the manufacturing method of a body.

First Step In the first step, green powder containing yttrium and zirconium and having an average primary particle diameter of 10 to 100 nm and a BET specific surface area of 3 to 30 m ² / g is molded to form a powder compact. Get the body.

What is necessary is just to prepare the composition of raw material powder so that it may become a composition of the zirconia sintered compact of this invention. For example, an oxide serving as a supply source of each component can be used. As the oxide, for _example, it can be used ZrO _2, Y 2 _{O 3} and the like. In the present invention, zirconia powder (particularly partially stabilized zirconia powder) containing 3 to 5.5 mol% (preferably 3 to 5 mol%) of yttria as a stabilizer can be suitably used as the raw material powder.

  In addition, the raw material powder can be appropriately blended with components (transition elements, rare earth elements, etc.) for coloring the obtained zirconia sintered body, if necessary.

Furthermore, 1) aluminum oxide alone or 2) aluminum oxide and magnesium oxide may be added to the raw material powder within a range of 0.5 wt% or less (preferably 0.1 to 0.5 wt%). By adding aluminum oxide Al ₂ O ₃ or the like within the above range, higher strength can be obtained while maintaining excellent translucency. In the above 2), when aluminum oxide and magnesium oxide are used in combination, the ratio of both is not limited, but it is usually sufficient that the weight ratio is aluminum oxide: magnesium oxide = 1: 10 to 1: 0. . In the present invention, it is preferable to add aluminum oxide alone.

Addition of aluminum oxide Al ₂ O ₃ to zirconia improves the sinterability of the raw material powder and enables sintering at a lower temperature, thereby reducing the particle size of the sintered body and improving the mechanical strength. Is known. However, in the prior art, Al ₂ O ₃ hardly dissolves in zirconia and easily segregates at the grain boundary part of the sintered body, so that it tends to be harmful to translucency. In the present invention, Al ₂ O ₃ has the same effect of improving the sintering characteristics, but the transmittance of the zirconia sintered body to which Al ₂ O _{3 is} added remains at the same level as that of the additive-free product. According to the common technical knowledge so far, Al ₂ O ₃ is segregated at the grain boundary part of the zirconia sintered body as described above, so that the optical properties should be deteriorated. I can't. In the HP method or the HIP method, defects such as pores can be forcibly eliminated by high-pressure sintering, so that the sintering is completed in a short time after the elimination of the defects. On the other hand, in the present invention, the defects in the material are gradually removed during the sintering process by evacuating the pores or substituting oxygen to raise and maintain the temperature, while the added Al ₂ O ₃ may also be a condition that allows more uniform solid solution in the zirconia sintered body (zirconia particles). In this case, if it is considered that once dissolved Al ₂ O ₃ is difficult to segregate at the grain boundary part of zirconia during the cooling process of sintering, the Al ₂ O ₃ -added zirconia sintered body of the present invention is a conventional product. Although it is a reason for exhibiting optical characteristics superior to those of the HIP method, scientific elucidation has not been achieved at this stage. In the ZrO ₂ -Al ₂ O ₃ phase diagram shown in Figure 4378 of Phase Diagram for Ceramics (by The American Ceramics Society), Al ₂ O ₃ is dissolved in zirconia in the range of about 1% by weight or less. It is considered possible, and the amount of solid solution of Al ₂ O ₃ decreases with cooling. The volume diffusion coefficient of Al ions in the zirconia solid is unknown, but the diffusion coefficient of Al ions in zirconia in the sintering temperature range described in the present invention is not so large as to cause grain boundary precipitation (Al is not enough). This does not cause segregation in the vicinity of the grain boundary), and is consistent with the fact that the product of the present invention is superior in optical properties to HIP having the same Al ₂ O ₃ concentration. However, even if the present invention can exert the effect of adding Al ₂ O ₃ to the maximum, addition of excess Al ₂ O ₃ (amount that cannot be dissolved in principle) must be avoided. In this respect, the amount added is preferably 0.5% by weight or less. Of course, since the same effect can be obtained by adding Al ₂ O ₃ and MgO or adding spinel (MgAl ₂ O ₄ ), Al ₂ O ₃ alone or a combination of Al ₂ O ₃ and MgO is also within the scope of the present invention. It becomes.

The average primary particle diameter of the raw material powder is 10 to 100 nm and the BET specific surface area is 3 to 30 m ² / g. When outside these ranges, any of mechanical strength, translucency, hydrothermal deterioration resistance, etc. of the obtained zirconia sintered body may be inferior.

  Preparation (mixing) of the raw material powder may be performed using a known or commercially available mixer or the like, and may be either dry or wet. In the case of the wet type, for example, an alcohol organic solvent such as ethanol (a modified type that is an industrial alcohol) or isopropyl alcohol may be used. Moreover, well-known additives, such as an organic binder (synthetic resin binders, such as an acrylic resin binder), a dispersing agent, can also be mix | blended suitably as needed.

  In the present invention, two or more kinds of raw material powders having different yttria contents can be mixed and used. For example, yttria 3 mol% and 4 mol% of two kinds of zirconia powders can be used in combination (that is, raw materials having different chemical potentials). Thereby, sintering is further promoted, and it becomes easier to obtain a target zirconia sintered body.

  In the first step, it is desirable to granulate the raw material powder prior to forming the green compact. In the present invention, 1) a method of granulating a raw material powder without using any synthetic resin binder (binder free) or 2) a method of granulating a raw material powder using a synthetic resin binder, which is highly plasticized By forming the product (granule), a green compact having a small pore size (and few pores having a large pore size) and a sharp distribution can be more reliably formed.

  The granulation method is not particularly limited, and known granulation methods such as stirring granulation, tumbling granulation, spray drying and the like can be adopted. In particular, a) a raw material powder is included and a synthetic resin binder is used. A granulated product can be suitably obtained by spray-drying a slurry containing no (binder-free) slurry or b) a slurry containing a raw material powder and a synthetic resin binder. In any case, a solvent (for example, water, alcohols, etc.) used in a known granulation method can be used as appropriate.

  The average particle size of the granulated product in the cases 1) and 2) is not limited, but it is usually desirable to be about 10 to 100 μm. When granules of other sizes are generated by a spray dryer, etc., they can be classified by a sieve and excluded. Although it does not restrict | limit especially as a synthetic resin type | system | group binder, For example, an acrylic binder is mentioned. The kind of acrylic binder is not limited, and a known or commercially available one can be used. For example, Acrylic acid alkyl methacrylic acid polyoxyalkylene glycol monoester acrylic acid copolymer resin solution and the like can be suitably used.

  The method for molding the raw material powder is not particularly limited, and for example, uniaxial press (die press) molding, cold isostatic pressing (CIP method) can be employed. For example, a green compact can be suitably obtained by the CIP method after uniaxial press molding as the primary molding. The pressure for CIP molding may be in the range of 50 to 500 MPa.

  When molding, it can be set as appropriate according to the particle size of the raw material powder to be used, the composition of the raw material powder, etc., but the green compact has (1) an average pore diameter of 0.02 to 0.3 μm, (2 The maximum pore diameter is 50 μm or less, and (3) the volume ratio of pores having a pore diameter of 5 μm or more to the total pore volume is preferably adjusted to 5% or less (particularly 2% or less). Thereby, the zirconia sintered compact which has the outstanding translucency and hot water deterioration property with high mechanical strength can be obtained.

  The obtained green compact can be calcined as necessary. In particular, when an organic substance such as a binder is included, it is preferably calcined (degreasing) to remove it. Although the calcining temperature is not limited, it may be usually 500 to 1000 ° C. The calcining atmosphere may be, for example, the atmosphere or an oxidizing atmosphere.

Second Step In the second step, the green compact is fired at 1300 to 1600 ° C. in a vacuum atmosphere of 10 ¹ to 10 ⁻⁴ Pa, or in an oxygen-containing atmosphere with an oxygen concentration of 50% or more (hereinafter “high oxygen” The method of baking at 1300-1600 degreeC below atmospheric pressure is implemented. Thereby, the sintered compact of this invention can be obtained.

The firing temperature is 1300 to 1600 ° C. and varies appropriately with the amount of Y ₂ O _{3 in} zirconia, but is particularly preferably 1350 to 1550 ° C. The firing time can be appropriately set according to the firing temperature, firing atmosphere, and the like.

The firing atmosphere may be about 10 ¹ to 10 ⁻⁴ Pa, preferably 10 ⁻¹ to 10 ⁻⁴ Pa in the case of a vacuum atmosphere. When the zirconia sintered body is reduced after vacuum sintering and is not white to milky white (for example, light yellow or gray), the target sintered body is annealed at a temperature of 900 to 1400 ° C. in an atmosphere containing oxygen. Is obtained.

  In the case of a high oxygen atmosphere, the oxygen concentration is 50% or more, preferably 90% or more. The gas other than oxygen may be an inert gas such as nitrogen gas or argon gas. However, He gas is more preferable from the viewpoint that the remaining pores can be removed smoothly. In the case of a high oxygen atmosphere, oxygen gas is preferably 50 to 100% and nitrogen or inert gas is preferably 0 to 50%. Although the pressure in a high oxygen atmosphere is not limited, it may be set to atmospheric pressure or lower (normal pressure or lower), and is preferably within a pressure range of about 0.1 to 1 atm.

In the present invention, firing is performed in a vacuum or a high oxygen atmosphere, but this material system is extremely effective when the zirconia green compact is densified (exclusion of pores) during the sintering process. In particular, oxygen gas enters and replaces the voids (pores) in the zirconia green compact during the sintering process, and can be easily excluded from the sintered body in the middle and final stage sintering. It is estimated that the amount of pores can be drastically reduced. In the synthesis of translucent ceramics, for example, in the case of alumina, it is generally known to use hydrogen gas or use HIP. In the case of a zirconia sintered body, an example of obtaining translucency using a sintering aid such as TiO ₂ in a stabilized zirconia sintered body has been reported, but even a zirconia having a cubic structure is excellent. It is not easy to obtain a sintered body having translucency. Since partially stabilized zirconia belonging to tetragonal crystal is more difficult to transmit light, the pores are forcibly eliminated using high-pressure sintering technology of HIP or HP, that is, the fracture start point and the light scattering source inside the material are reduced. In this way, mechanical strength and permeability are ensured. However, considering the material technology, it is unlikely that the strength of zirconia itself will change due to high-pressure sintering, and the reduction of structural defects such as pores in the zirconia sintered body will lead to higher strength and higher light transmission. It is considered an essential reason. Therefore, by providing a new means for reducing the structural defects of the material (atmospheric pressure sintering technology that achieves both performance and economy, instead of conventional high pressure sintering), it can be used as a dental zirconia sintered body. There is a difference in that high performance can be imparted. More preferably, in the present invention, not only oxygen and the like are used, but primary particles suitable for sintering are first selected, and the raw material powder is prepared using an acrylic binder (or without using a synthetic resin binder). It is premised on the formation of a highly compact granule in the granulation process to produce a compact with a small pore size and sharp distribution. If the pores of 5 μm or more in the green compact after CIP molding become 5% or more of the total pores, relatively large residual pores exist in the sintered zirconia sintered body, and the mechanical strength is reduced. The pores of 5 μm or more in the powder should be controlled to 5% or less, preferably 2% or less of the total pore amount. By firing the green compact with controlled pore size and distribution in the vacuum or preferably in an oxygen atmosphere with a certain concentration or higher, a sintered zirconia body with fewer pores can be obtained, and its characteristics have been desired so far. It will be suitable for dental use. If oxygen is present in the pores of the green compact before firing (the pores are filled with oxygen gas by the introduction of oxygen gas), the oxygen gas can easily be removed outside during sintering. . Zirconia (especially cubic zirconia) is used as a solid electrolyte material because it has the property of easily taking oxygen gas in contact with it into the solid. Residual pores existing inside zirconia using this property There is no technical idea other than the present invention in which (oxygen gas) is removed, the structure defects inside the zirconia sintered body material are drastically reduced, the mechanical strength is prevented from being lowered, and the translucency is enhanced. In addition to oxygen, vacuum, He, hydrogen, etc. are theoretically conceivable as gas species to be substituted for the pores of the green compact, but as a result of experiments in the present invention, only oxygen and vacuum are suitable for the application of the present invention. It was confirmed. If the atmosphere during sintering is vacuum (and if oxygen is set to 100%, it is natural that the transmittance is maximized, and the variation in the three-point bending strength is about 50% oxygen) Additional functions such as being reduced to about 1/2 to 1/3 have been confirmed, and excellent effects are also exhibited from the viewpoint of quality assurance and quality control. This is considered to be because it is not effective for eliminating pores in the zirconia sintered body and that structural defects (pores) remain in the material.

<Embodiment 1>
FIG. 1 shows the pore size distribution in a green compact obtained by CIP treatment in the present invention. The sample preparation and measurement method were measured by a general mercury intrusion method according to the methods described in the description of Examples and Comparative Examples described later. The pore size of the green compact (Good type) produced according to the present invention was concentrated in the portion of 0.2 to 0.02 μm, and coarse pores exceeding 5 μm were not detected. When this green compact is sintered, there are almost no coarse pores in the sintered body, and a zirconia sintered body excellent in mechanical strength and translucency can be obtained. On the other hand, in the green compact (Bad type) produced by the prior art, the pore size was also concentrated in the portion of 0.2 to 0.01 μm, but there are also coarse pores exceeding 5 to 10 μm. . When this green compact was sintered, coarse residual pores existed inside the zirconia sintered body, and the sintered body was insufficient in translucency and strength.

<Embodiment 2>
FIG. 2 shows the result of observation of the product of the present invention and a 3.3 mol% Y ₂ O ₃ -added zirconia sintered body (thin sample having a thickness of 200 μm) produced by a transmission optical microscope. In samples A and D, which are products of the present invention, no residual climate is observed in the measurement field of view. Samples B and D are also products of the present invention, but there are residual pores within several to 5 μm, but the residual pore amount is 0.3% or less. Samples E and F were produced by the conventional technique, but a relatively large number of 10 to 50 μm coarse pores were observed in the zirconia sintered body, and a large number of relatively small pores of 10 to several μm were detected. Also,
The transmittances of the manufactured samples A to D of the 3 mm-thick samples were 12, 10, 10, 11, 8, and 7%, respectively. On the other hand, as for the three-point bending strength, samples A to D showed 950 MPa or more, whereas the bending strengths of samples E and F not within the scope of the present invention were as low as 510 and 360 MPa.

<Embodiment 3>
3- (a) in FIG. 3 shows a diameter of 17 mm × thickness of the 3.5 mol% Y ₂ O ₃ -added zirconia sintered body of the present invention and the 2.6 mol% Y ₂ O ₃ -added zirconia sintered body of the prior art. The state is shown when the sample is processed into an 8 mm tablet (both sides are ground and polished) and the sample is irradiated with white LEDs from below. Although all the sintered bodies used commercially available zirconia powder, the product of the present invention is granulated using an acrylic binder. After die molding, CIP molding was performed at a pressure of 196 MPa. In the present invention, a zirconia sintered body was prepared by sintering in a 100% oxygen atmosphere at 1400 ° C. for 5 hours, and the conventional product in air at 1320 ° C. for 3 hours. As is apparent from the results of FIG. 3, the product of the present invention can easily pass LED light, and it can be seen that the entire sample is brightly shining. In contrast, prior art materials hardly allow light transmission and the surface is only whitened by scattering. 3- (b) is obtained by sintering a green compact made into a crown shape (anterior teeth and back teeth) with a CAD-CAM system using the technique of the present invention under the same conditions as described above. The photograph is observed under natural light, but has aesthetics similar to natural teeth with nerves. The lower part of the photograph is irradiated with halogen lamp light from the lower part. It is clear that light passes from the inside of the artificial dental crown to the outside, and the optical features of the product of the present invention can be easily confirmed.

<Embodiment 4>
4-6 shows an example of a sintering apparatus suitable for producing the translucent zirconia sintered body of the present invention. These are examples of the outline of the sintering apparatus, and are not particularly limited thereto.

The sintering apparatus (sintering apparatus A) of FIG. 4 includes 1) a firing furnace 9 provided with a heater 1 outside the furnace, 2) a sample stage 5 installed in the firing furnace 9, and 3) the inside of the firing furnace 9 being sealed. 4) Rotary pumps (vacuum pumps) 2 for reducing the pressure inside the firing furnace 9 and 5) Gas cylinders 4 for introducing gas into the firing furnace 9. As the firing furnace 9, for example, a ceramic firing furnace such as an alumina firing furnace can be suitably used. Further, the shape of the firing furnace is not limited, and may be any of a rectangular parallelepiped, for example, in addition to a tube shape as shown in FIG. In the sintering apparatus A, the rotary pump 2 and the gas cylinder 4 are connected to the firing furnace 9 via a pipe 12 and a valve 13. As shown in FIG. 4, the exhaust port and piping for exhausting the gas of the firing furnace 9 may be installed via a flange. Further, the flow meter 3 can be provided between the gas cylinder 4 and the firing furnace 9. As long as the inside of the baking furnace 9 can be heated, the shape, arrangement | positioning location, number, etc. of the heater 1 are not specifically limited. Although the kind of heating element used as the heater 1 is not limited, for example, molybdenum silicide (MoSi system), keramax (LaCrO ₃ system), siliconite (SiC), carbon (C), and the like can be suitably used. . A commercial item can also be used for these heat generating bodies. Moreover, although the heater 1 may be arrange | positioned as it is, in order to improve thermal efficiency, it is preferable that it is covered with the heat insulating material 7. FIG.

  The zirconia green compact molded into a predetermined shape is put into the firing furnace 9, and the inside is reduced in pressure (or vacuum) by the rotary pump 2. After shutting off the vacuum system, the atmosphere can be adjusted by gradually introducing an atmosphere gas (for example, 100% oxygen gas or 50% oxygen + 50% He gas) into the firing furnace 9. Although it is possible to introduce the atmospheric gas directly without first reducing the pressure with the rotary pump, it is better to introduce the atmospheric gas after depressurizing the inside of the firing furnace as described above. The transmittance can be further increased. The reason for this is considered to be that the removal of the pores becomes smooth because the gas component present in the open pores inside the green compact is removed and the introduced gas can be easily replaced with this portion. In particular, the translucency of the zirconia sintered body sintered under the condition in which 100% oxygen gas is introduced is very excellent.

  The temperature is raised at a rate of, for example, about 20 to 200 ° C./hr, particularly in the temperature range of 900 ° C. or higher where firing shrinkage starts while performing program control capable of PID control while flowing the introduced gas quantitatively. Thus, densification is promoted, and finally, a sintered body balanced in the three elements of mechanical strength, translucency and hydrothermal deterioration resistance can be obtained. In order to obtain a conventional translucent zirconia sintered body, three steps of (1) normal pressure sintering → (2) HIP sintering → (3) annealing (decoloration by oxidation treatment) are necessary and long. Delivery time and high cost (initial cost (expensive equipment cost) and running cost (3 times of sintering)) are required. In this regard, it is needless to say that this apparatus produces a great economic effect because the apparatus cost of one-tenth or less and a single firing process are sufficient in this apparatus.

  The sintering apparatus (sintering apparatus B) in FIG. 5 includes 1) a firing furnace (electric furnace) 9 provided with a heater 1 in the furnace, 2) a sample stage 5 installed in the firing furnace 9, and 3) a firing furnace. A flange 8 for sealing the inside of the furnace 9, 4) a rotary pump (vacuum pump) 2 for depressurizing the inside of the firing furnace 9, and 5) a gas cylinder 4 for introducing gas into the firing furnace 9. As the firing furnace 9, for example, a ceramic firing furnace such as an alumina firing furnace can be suitably used. In the sintering apparatus B, the rotary pump 2 and the gas cylinder 4 are connected to the firing furnace 9 via a pipe 12 and a valve 13. As shown in FIG. 5, an exhaust port and piping for exhausting the gas of the firing furnace 9 can be installed. Further, the flow meter 3 can be provided between the gas cylinder 4 and the firing furnace 9. As long as the inside of the baking furnace 9 can be heated, the shape, arrangement | positioning location, number, etc. of the heater 1 are not specifically limited. Since the sintering apparatus B has the box-type firing furnace 9, it is cheaper than the sintering apparatus A and can process a large amount of materials at a time. Whether to use the sintering apparatus A or the sintering apparatus B may be appropriately selected depending on the properties of the required material.

  The sintering apparatus (sintering apparatus C) of FIG. 6 is an apparatus suitable for performing vacuum firing. In the sintering apparatus C, 1) a vacuum chamber 11 provided with a heater 1 in the furnace, 1) a sample stage 5 installed in the vacuum chamber 11, 3) a rotary pump (vacuum pump) for depressurizing the inside of the vacuum chamber 11 ) 2 and a turbo-molecular pump 10. In the sintering apparatus B, the vacuum chamber 11 is preferably water-cooled (water-cooled vacuum chamber). As long as the inside of the baking furnace 9 can be heated, the shape, arrangement | positioning location, number, etc. of the heater 1 are not specifically limited. As the heater 1, a metal heater such as tungsten, molybdenum, platinum, or a carbon heater can be preferably used. Depending on the type of heater, only a rotary pump may be used, but a diffusion pump, molecular turbo pump, or the like may be used in addition to the rotary pump for the purpose of improving the life of the heater and the performance of the material. Even with the vacuum firing apparatus, the same or better effect than the atmosphere control type firing furnace can be exhibited.

  The features of the present invention will be described more specifically with reference to the following examples and comparative examples. However, the scope of the present invention is not limited to the examples.

Example 1
A commercially available partially stabilized zirconia powder (containing 3.05 mol% of yttria as a stabilizer, an average primary particle size of 30 nm, and a BET specific surface area of 6.9 m ² / g) was used as a raw material powder. 300 g of this raw material powder was mixed with 450 mL of ethanol and 15 g of a commercially available acrylic binder (product name “KS910” manufactured by Nippon Kayaku Co., Ltd.) and mixed and pulverized with zirconia balls for 12 hours. The obtained slurry was spray-dried with a spray dryer to obtain granules having an average particle size of 40 μm. This granule was press-molded using a mold to obtain a substrate of 10 mm × 15 mm × 70 mm. The substrate was vacuum-packed, CIP-molded at a pressure of 196 MPa, and degreased at 700 ° C. for 3 hours in the atmosphere to remove organic substances inside the material. Next, it was fired at 1370 ° C. in an atmosphere having an oxygen concentration of 100%. A zirconia sintered body (test body) was thus obtained.

Examples 2-42 and Comparative Examples 1-12
A zirconia sintered body was produced in the same manner as in Example 1 except that the production conditions were changed as shown in Tables 1 to 9. Tables 1 to 7 show the present invention, and Tables 8 to 9 show comparative examples. Other changes are as follows.
Examples 25 to 26 are based on Example 15 when the CIP pressure is 50 and 500 MPa, respectively.
In Examples 27 to 32, a sintered body was prepared using a zirconia raw material prepared on a lab base, and the main difference from a commercially available raw material is the primary particle size and the value of the specific surface area associated with the particle size variation. .
Examples 33 to 38 show characteristics of a zirconia sintered body produced by solid phase sintering using a commercially available zirconia raw material and a commercially available yttria raw material.
Examples 39 to 42 show the characteristics of a zirconia sintered body having a yttria content in the range of 4.2 to 5.5 mol% using a commercially available partially stabilized zirconia raw material. In preparing the product of this example, the acrylic binder used in Examples 1 to 38 was excluded, a slurry was formed only with zirconia powder and ethanol, and this slurry was spray-dried with a spray dryer to synthesize resin components. Granules containing no were produced. The subsequent manufacturing process was the same as in Examples 1-38.
In Comparative Examples 1 and 2, 3 mol% Y ₂ O ₃ -containing zirconia powder prepared on a lab base was used instead of a commercially available powder. In Comparative Examples 3 and 4, sintering was performed at an oxygen concentration of 50% or less (Comparative Example 3 was sintered at a sintering temperature of 1620 ° C. and outside the scope of the invention).
In Comparative Examples 10 to 11, sintering was performed with CIP molding pressures of 30 and 600 MPa, respectively, and in Comparative Example 11 with an oxygen concentration of 5%.
In Comparative Examples 13 to 14, 15 g of a 20% solution of PVA (polyvinyl alcohol) and PVB (polyvinyl butyral) binder was used. In Comparative Example 13, a slurry was prepared using distilled water as a solvent, and spray drying was performed.
In Comparative Examples 7 to 8, a raw material (single raw material or mixed raw material) having a composition with a Y concentration outside the range of the present invention was used. In particular, in Example 9, the sintering temperature was 1610 ° C.

Test example 1
In the above examples and comparative examples, the crystal particle size, residual pore volume, ratio of pores having a pore diameter of 10 μm or more, bending strength, phase change after hydrothermal treatment, mineral phase and transmittance were measured. . The results are shown in Tables 1-9.

In each of these tables, the properties of the raw material powder in the process of preparing the specimen, the presence or absence of addition of Al ₂ O ₃ or MgO, the average particle diameter of the granules, the average pore diameter of the green compact, and the pore diameter of 5 μm or more The proportion of the pores, the firing atmosphere and temperature, the average crystal grain size of the sintered body, the apparent porosity of the sintered body, the number of pores having a pore diameter of 10 μm or more in the sintered body, the bending strength, the crystal phase after hydrothermal treatment, The mineral phase after sintering and the transmittance are also shown.

The measuring method of each physical property is as follows.
(1) Average particle diameter of granules obtained by spray drying 100 spray-dried granules were arbitrarily taken out, and the average size (diameter) was calculated from observation with an optical microscope or scanning electron microscope (SEM).
(2) Average pore diameter of the green compact A green compact of 16 mm in diameter and 10 mm in height formed by CIP molding at 196 MPa was calcined at 700 ° C. with little firing shrinkage, and the green compact was about 7 mm × 7 mm. After processing to × 7 mm, pore distribution was determined by mercury porosimetry using AutoPore III of Micromeritics, and based on this, the average pore diameter and the volume ratio occupied by pores having a pore diameter of 5 μm or more were obtained.
(3) Average crystal grain size of sintered body The sintered sample was mirror-polished and then thermally etched at a sintering temperature or lower. The average crystal particle diameter of the sintered body was calculated from surface photographs taken arbitrarily at five times by SEM at 10,000 times.
(4) Apparent Porosity of Sintered Body The porosity in the sintered body was measured by the Archimedes method (calculated from the measurement of dry weight, moisture content, and weight in water) to measure the apparent specific gravity, bulk specific gravity and apparent porosity.
(5) Number of residual pores First, the sintered zirconia sintered body was cut to produce a test piece having a thickness of 200 μm (the test piece was double-sided mirror polished), and the residual pores present inside the material were examined with a transmission microscope. Count size and quantity. More specifically, the number of pores having a pore diameter of 10 μm or more was counted in the area of a measurement field of 2 mm × 2 mm in a transmission microscope (magnification 200 times).
(6) Bending strength Three-point bending strength was measured. The three-point bending strength is measured using a universal testing machine “Auto Gerafu DCS-2000” (manufactured by Shimadzu Corporation), and a specimen having a width of 4 mm, a thickness of 3 mm and a length of 40 mm is span length based on JIS-R-1601. The test was performed under the conditions of 30 mm and a crosshead speed of 0.1 mm / min. A test piece was prepared for each sample, and a bending test was performed.
(7) Monoclinic / tetragonal ratio after hydrothermal treatment Monoclinic crystals detected by conducting powder X-ray diffraction analysis of the sample after being treated at 180 ° C for 5 hours using an autoclave (hydrothermal synthesizer) Diffraction of the strongest peak of zirconia ((-1,1,1) plane, 2θ = 28 °, d = 3.1647) and diffraction of the strongest peak of tetragonal zirconia ((1,0,1) plane, 2θ = 28) °, d = 2.9597).
(8) Mineral phase of sintered body The mineral phase of the sintered body is a tetragonal fluorite-type crystal phase (I) containing 3 mol% or less of yttria and 5 mol% or more by a general powder X-ray diffraction method. Measurement was carried out by separating into a cubic fluorite crystal phase (II) containing yttria.
(9) Transmittance In this measurement, a transmission densitometer 361T (manufactured by X-rite) was used, and a zirconia sintered body produced to a thickness of 3 mm was irradiated with a vertically transmitted light beam (400 to 700 nm (peak 570 nm) light). Then, the ratio of the state where there is no sample expressed in log (logarithm) was defined as the optical density D, and the transmittance was calculated from 1 ÷ 10 ^D × 100. The beam width is a circle with a diameter of 1 mm.

*) Since the vacuum-fired sample was reduced and light yellow or light gray, a sample subjected to heat treatment at 1000 ° C. in air for 3 hours was used as a physical property measurement sample.

  As can be seen from the comparison of the examples and comparative examples, the present invention is found to be a material with a very high balance of mechanical strength, optical properties, and durability (water resistance. Also, HIP processed products. Compared to the above, it can be easily judged that the mechanical strength is not inferior, it has further excellent permeation characteristics, and is excellent in water resistance.

  Although the zirconia sintered body according to the present invention is a tetragonal system or a mixed system of tetragonal crystals and cubic crystals, it is characterized by having excellent mechanical strength, translucency and water resistance. In addition, the economic efficiency surpasses the zirconia sintered body produced by the conventional HIP method. Since the properties of the obtained sintered body are sufficiently satisfactory for industrial needs, particularly dental applications, application to this field is expected.

Claims (13)

A zirconia sintered body containing 3 to 5.5 mol% of yttria, (1) apparent porosity is 1% or less, and (2) in an area of 2 mm × 2 mm in a thin piece sample having a thickness of 0.2 mm The zirconia sintered body is characterized in that the number of pores having a pore diameter of 10 μm or more is 30 or less, and (3) the average crystal grain size is 0.2 to 1.5 μm. The zirconia sintered body according to claim 1, wherein the transmittance in the wavelength range of 400 to 700 nm at a sample thickness of 3.0 mm is 7% or more. The zirconia sintered body according to claim 1 or 2, wherein the three-point bending strength is 800 to 1500 MPa. The crystal phase is (1) tetragonal fluorite crystal phase 40 to 100% by volume containing 3 mol% or less yttria and (2) cubic fluorite crystal phase 0 to 5 mol% or more yttria The zirconia sintered body according to any one of claims 1 to 3, comprising 60% by volume. The ratio of (strongest peak of monoclinic phase) / (strongest peak of tetragonal phase) in powder X-ray diffraction after hydrothermal treatment of the zirconia sintered body at 180 ° C. for 5 hours is 1 or less, Item 5. The zirconia sintered body according to any one of Items 1 to 4. The zirconia sintered body according to any one of claims 1 to 5, comprising at least one of an aluminum component and a magnesium component in a range of 0.5% by weight in terms of oxide. The dental material containing the zirconia sintered compact in any one of Claims 1-6. An orthodontic bracket including the zirconia sintered body according to any one of claims 1 to 6. A method for producing a zirconia sintered body containing yttria,
(1) First to obtain a green compact by molding a raw material powder containing yttrium and zirconium and having an average primary particle diameter of 10 to 100 nm and a BET specific surface area of 3 to 30 m ² / g or a granulated product thereof. Process,
(2) Zirconia sintering including a second step in which the green compact is fired at 1300 to 1600 ° C. under atmospheric pressure in a vacuum atmosphere of 10 ¹ to 10 ⁻⁴ Pa or in an oxygen-containing atmosphere with an oxygen concentration of 50% or more. Body manufacturing method. The manufacturing method of Claim 9 whose raw material powder is a powder of the zirconia containing 3 to 5.5 mol% yttria as a stabilizer, and the purity is 99% or more. The green compact has (1) an average pore diameter of 0.02 to 0.3 μm, (2) a maximum pore diameter of 10 μm or less, and (3) a volume occupied by pores having a pore diameter of 5 μm or more with respect to the total pore volume. The manufacturing method of Claim 9 or 10 whose ratio is 5% or less. The production method according to any one of claims 9 to 11, wherein the raw material powder further contains at least one of aluminum oxide and magnesium oxide in a range of 0.5 wt%. The zirconia sintered compact obtained by the manufacturing method in any one of Claims 9-12.