Method for manufacturing zirconia composite ceramics and method for manufacturing dental zirconia ceramic prostheses

Abstract

To provide a method for efficiently producing zirconia composite ceramics having high bending strength, which can be suitably used as a zirconia ceramic prosthesis for dental use.SOLUTION: In a method for producing a zirconia composite ceramic, a "composite zirconia temporary sintered body" is prepared, is cut using a CAD / CAM system as necessary, and is then actually sintered at a temperature of 1,250-1,800°C. Thereafter, it is slowly cooled to a specific primary cooling temperature in a range of 400-900°C at 100-900°C / hour. Subsequently, it is cooled to 50°C or less at 1,000-9,000°C / hour. The composite zirconia temporary sintered body comprises a temporary sintered body of a stabilized or partially stabilized zirconia powder containing zirconium oxide, a stabilizing agent consisting of yttrium oxide, and an aluminum oxide additive as a main structure, which is composited with a silicon dioxide component such as fine particles of silicon dioxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a zirconia composite ceramic and a method for producing a dental zirconia ceramic prosthesis. [Background technology]

[0002] In recent years, advances in information and communication technology (ICT) have led to the widespread adoption of computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies in the dental field. For example, CAD / CAM systems are increasingly used to fabricate dental prostheses. These systems utilize intraoral imaging to machine dental blanks made of nonmetallic materials. A dental blank is a workpiece (also known as a mill blank) that can be attached to a milling machine in a CAD / CAM system. It typically includes a workpiece and a holder for mounting the workpiece to the milling machine. Commonly known workpieces include solid blocks shaped like rectangular parallelepipeds or cylinders, or solid disks shaped like plates or discs.

[0003] Zirconia-based ceramic materials are often used as non-metallic materials because of their excellent strength and toughness, allowing for the fabrication of aesthetically pleasing dental prostheses. Because fully sintered zirconia-based ceramic materials are difficult to machine due to their strength, when using a CAD / CAM system to fabricate dental prostheses (hereinafter referred to as "zirconia prostheses") made of zirconia-based ceramics, pre-sintered zirconia-based ceramics pre-sintered at a relatively low sintering temperature are typically used as the machining target for zirconia dental mill blanks (also simply referred to as "zirconia mill blanks"). Based on CAD, which takes into account shrinkage that occurs during high-temperature sintering, the blank is then machined to a shape corresponding to the final prosthesis shape obtained by CAM, and then sintered to produce a dense, high-strength zirconia prosthesis.

[0004] Regarding zirconia-based ceramics, pure zirconia (zirconium oxide) undergoes a phase transition accompanied by a volume change depending on the temperature. Therefore, stress caused by the volume change during the cooling process after sintering can cause cracks and lead to a decrease in strength. To prevent this phase transition, stabilizers such as yttrium oxide, calcium oxide, and magnesium oxide have been added to stabilize zirconia or partially stabilized zirconia, which exist as a tetragonal or mixed crystal system of tetragonal and cubic crystals stable at high temperatures without transforming to the monoclinic system stable at low temperatures upon cooling. Such stabilized zirconia or partially stabilized zirconia is also used as the zirconia raw material powder used in zirconia mill blanks, and alumina (an additive) is commonly added to further increase strength. For example, Patent Document 1 describes a raw material powder that can be pressure-sintered to produce a zirconia sintered body that is particularly suited to anterior dentures and has both translucency and strength, and that contains "4.0 mol % to 6.5 mol % of yttria and less than 0.1 wt % of alumina, and has a BET specific surface area of ​​8 to 15 m. 2 / g」。

[0005] Incidentally, it is known that for sintered bodies of (partially) stabilized zirconia containing yttria (yttrium oxide) as a stabilizer, adjusting the amount of yttria added changes the ratio of tetragonal zirconia to cubic zirconia, resulting in corresponding changes in strength and transparency, as shown in Non-Patent Document 1. That is, as the yttria content increases, the content of cubic crystals, which contribute to improved transparency, increases, while the content of tetragonal crystals, which contribute to high strength, decreases. This results in a trade-off between high strength and high transparency. For this reason, when producing prosthetic appliances that require high transparency, such as for anterior teeth, transparency is prioritized, and "partially stabilized zirconia with an yttria content of 5 mol% or more," which is slightly weaker in strength, is generally used.

[0006] On the other hand, when producing molar prostheses or long-span bridges that require high strength, "stabilized zirconia or partially stabilized zirconia with an yttria content of 3.5 mol% or less," i.e., tetragonal zirconia, is generally used, but problems with strength and durability have been pointed out because low-temperature deterioration, which is thought to occur when the tetragonal phase transforms into the monoclinic phase in the presence of moisture, increases the crystal lattice volume and causes cracks (see Patent Document 2). Patent Document 2 also discloses a technology in which stabilized zirconia or partially stabilized zirconia is blended with strontium aluminate or spinel, preferably in an amount of 4 to 6 volume %, and then pre-sintered after molding, in order to improve the microscopic shear deformability (or resistance to polishing with a diamond loading tool) and aging resistance to hot water of the fully sintered body. Furthermore, Patent Document 2 discloses that a fully sintered body obtained by processing the thus obtained pre-sintered body and then sintering it has a structure in which a secondary phase made of the above-mentioned strontium aluminate or spinel, preferably having a particle size of 0.2 to 0.5 μm, is dispersed in a zirconia matrix phase having an average particle size of 0.1 to 2.0 μm, and that the hardness is reduced (compared to a case in which no secondary phase is present), and that optimizing the amount of the secondary phase depending on the type of secondary phase improves fracture toughness and improves residual strength after damage (Vickers hardness indenter), but does not consider improving initial bending strength.

[0007] Furthermore, Patent Document 3 discloses a technique for improving the adhesiveness of dental prostheses made of stabilized zirconia or partially stabilized zirconia obtained by sintering a molded body made of zirconia powder, without impairing the inherent aesthetic qualities or particularly increasing the manufacturing load. The technique involves infiltrating the surface layer of the stabilized or partially stabilized zirconia pre-sintered body with a penetrant made of a sol or the like obtained by mixing a catalyst made of tetraethyl orthosilicate (TEOS) and aluminum nitrate nonahydrate with water, followed by sintering, and then etching the surface layer. However, the bending strength of the material obtained in this manner is not examined.

[0008] Furthermore, Patent Document 4 describes a technique for producing a zirconia dental restoration having a highly translucent outer surface from a zirconia mill blank in a short time without glazing the zirconia dental restoration obtained after complete sintering, in which glass is made to exist in a region within a depth of 5 μm on at least a part of the outer surface of a porous dental zirconia restoration produced by cutting from the mill blank, and then sintered using a sintering protocol including a predetermined heating profile and cooling profile. However, Patent Document 4 does not consider the bending strength of the material obtained in this way. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2015 / 098765 Brochure [Patent Document 2] Patent No. 6333254 [Patent Document 3] Special Publication No. 2007-534368 [Patent Document 4] Special Publication No. 2021-515754 [Non-patent literature]

[0010] [Non-Patent Document 1] "CAD / CAM Material Complete Guidebook: Clinically Useful Material Selection and Adhesion Operations," by Kiyoji Ban, published by Ishiyaku Publishing Co., Ltd., December 20, 2017, pp. 18-20 Summary of the Invention [Problem to be solved by the invention]

[0011] As mentioned above, when fabricating prosthetics for anterior teeth, where aesthetics (transparency) is important, low-strength zirconia is generally used, and further strengthening is required. Furthermore, even with high-strength tetragonal zirconia, further strengthening is required due to the problem of strength durability caused by low-temperature degradation.

[0012] Therefore, an object of the present invention is to provide a method for efficiently producing a zirconia composite ceramic having high bending strength that can be suitably used as a dental zirconia ceramic prosthesis, and a method for efficiently producing a dental prosthesis made of a zirconia composite ceramic having high bending strength using a CAD / CAM system. [Means for solving the problem]

[0013] The present invention solves the above-mentioned problems, and a first aspect of the present invention includes a pre-sintered body preparation step of preparing a composite zirconia pre-sintered body, which comprises 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, 0.005 to 0.3 parts by mass of an aluminum oxide additive, and 0.05 to 5.0 parts by mass of silicon dioxide or a precursor thereof (however, the parts by mass of the silicon dioxide precursor represent parts by mass converted into silicon dioxide), and which contains the pre-sintered body of zirconium oxide as a main structure; a sintering step of sintering the composite zirconia pre-sintered body prepared in the pre-sintered body preparation step at a temperature of 1250 to 1800°C; and A method for producing zirconia-based ceramics, comprising a cooling step of cooling the sintered body sintered in the sintering step, The cooling step includes a first cooling step in which the sintered body is cooled at a cooling rate of 100 to 900 (°C / hour) {=1.7 to 15.0°C / min} to a primary cooling temperature, which is a predetermined temperature selected from a range of 400 to 900°C, and a second cooling step in which the sintered body cooled to the primary cooling temperature in the first cooling step is cooled at a cooling rate of 1000 to 9000 (°C / hour) {=17.0 to 150.0°C / min} to a temperature of 50°C or less. The present invention relates to a method for producing a zirconia composite ceramic.

[0014] In the first embodiment of the method for producing a zirconia composite ceramic (hereinafter also referred to as "the method for producing a zirconia composite ceramic of the present invention"), the preliminary sintered body preparation step is (A) forming a first raw material composition containing a zirconia-based powder containing 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, and 0.005 to 0.3 parts by mass of an aluminum oxide additive into a predetermined shape, and then calcining the resulting material at 600 to 1200°C to obtain a microporous calcined body having a relative density of 45 to 65% and pores that are open to the outside; and The method includes a step of sorbing 0.05 to 5.0 parts by mass of silicon dioxide fine particles relative to 100 parts by mass of zirconium oxide into the pores of the microporous pre-sintered body obtained in the step; A step of preparing a composite zirconia pre-sintered body in which fine particles of silicon dioxide are sorbed in the pores of the microporous pre-sintered body; or (B) a raw material composition preparation step of preparing a second raw material composition in which a zirconia-based powder containing 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, and 0.005 to 0.3 parts by mass of an aluminum oxide additive, and 0.05 to 5.0 parts by mass of a "silicon dioxide precursor" made of "amorphous silicon dioxide particles having an average primary particle size of 1 to 500 nm as measured by a dynamic light scattering method" and / or "a silicon dioxide source material made of a silicon-containing substance that can be converted into a silicon dioxide compound by sintering" are uniformly dispersed; a molding step of molding the second raw material composition to obtain a molded body having a predetermined shape; and A preliminary sintering step of preliminary sintering the compact at 600 to 1200 ° C.; It is preferable that the pre-sintering step is a step of preparing a composite zirconia pre-sintered body made of the pre-sintered body obtained in the pre-sintering step.

[0015] A second aspect of the present invention provides a cutting process for obtaining a semi-finished product having a shape corresponding to the shape of a desired dental prosthesis by cutting, using a CAD / CAM system, a zirconia dental mill blank having a cutting portion made of a composite zirconia pre-sintered body, the mill blank comprising 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, 0.005 to 0.3 parts by mass of an aluminum oxide additive, and 0.05 to 5.0 parts by mass of silicon dioxide or a precursor thereof (however, the parts by mass of the silicon dioxide precursor are expressed as parts by mass of silicon dioxide), and the pre-sintered body of zirconium oxide as a main structure; sintering the semi-finished product obtained in the above step at a temperature of 1250 to 1800 ° C; and A method for producing a dental zirconia ceramic prosthesis, comprising a cooling step of cooling the sintered body obtained in the sintering step, The cooling step includes a first cooling step in which the sintered body is cooled at a cooling rate of 100 to 900 (°C / hour) to a primary cooling temperature, which is a predetermined temperature selected from the range of 400 to 900°C, and a second cooling step in which the sintered body cooled to the primary cooling temperature in the first cooling step is cooled at a cooling rate of 1000 to 9000 (°C / hour) to a temperature of 50°C or less. The present invention relates to a method for producing a dental zirconia ceramic prosthesis (hereinafter also referred to as "the method for producing a dental zirconia prosthesis of the present invention"). [Effects of the Invention]

[0016] According to the method for producing a zirconia composite ceramic of the present invention, it is possible to improve the bending strength of the resulting sintered body while maintaining the characteristic of conventional stabilized or partially stabilized zirconia, that is, not undergoing a phase transition accompanied by a large volume change during the cooling process after sintering.

[0017] Furthermore, according to the method for producing a dental zirconia prosthesis of the present invention, it is possible to obtain a dental zirconia prosthesis having both high translucency and strength. DETAILED DESCRIPTION OF THE INVENTION

[0018] As a result of investigations conducted by the present inventors to solve the above-mentioned problems, they discovered that when a zirconia composite ceramic is prepared in which an appropriate amount of amorphous silica is present at the crystal grain boundaries of stabilized zirconia or partially stabilized zirconia, the strength is improved without reducing transparency, and that such a zirconia composite ceramic can be obtained by sintering a pre-sintered body of a raw material powder composition that serves as the raw material for stabilized zirconia or partially stabilized zirconia, combined with silicon dioxide or its precursor (a compound that is converted to silicon dioxide by firing), and have already reported this discovery (Patent Application Nos. 2020-188760 and 2021-129542).

[0019] Specifically, the researchers report that by sintering a composite zirconia pre-sintered body obtained by a method in which "crystalline zirconium oxide powder containing a stabilizer and an aluminum oxide additive is formed into a predetermined shape and then pre-sintered at 600 to 1200°C to obtain a microporous pre-sintered body with a relative density of 45 to 65%, and then immersing this pre-sintered body in a sol in which fine silicon dioxide particles are dispersed in a dispersion medium to sorb the silicon dioxide particles into the pores of the pre-sintered body, and then removing the dispersion medium" (hereinafter also referred to as the "immersion method"), or by "a method in which a raw material powder composition that serves as the raw material for stabilized zirconia or partially stabilized zirconia, containing silicon dioxide or its precursor (a compound that is converted to silicon dioxide by firing)" (hereinafter also referred to as the "pre-addition method") at a temperature of 1250 to 1800°C, the biaxial bending strength is improved compared to a case in which no silicon dioxide is contained.

[0020] The present invention was made based on the discovery that the biaxial bending strength of the resulting zirconia composite ceramics is affected by the cooling conditions after sintering these composite zirconia pre-sintered bodies, and also based on the discovery of a cooling method that can obtain high biaxial bending strength.

[0021] The reason for the improved biaxial bending strength of the zirconia composite ceramic obtained by sintering the composite zirconia pre-sintered body is believed to be that, based on the analysis by the present inventors, silicon dioxide is present at the grain boundaries between adjacent zirconia crystal grains and / or at the grain boundaries between adjacent zirconia crystal grains and aluminum oxide crystal grains. Therefore, it is believed that the silicon dioxide reduces the number of fracture initiation points under stress, inhibits crack propagation, or increases the interfacial strength, particularly in cubic crystals, thereby further increasing the strength. Furthermore, the reason for the increased strength achieved by employing the cooling method in the method for producing the zirconia composite ceramic of the present invention is believed to be that the slow cooling to a predetermined temperature followed by rapid cooling prevents cracks from occurring in the sintered body, and the rapid cooling of the silicon dioxide converts it into low-density silicon dioxide glass, which creates compressive stress in the zirconia composite ceramic, thereby increasing the strength.

[0022] The methods for producing the zirconia composite ceramic of the present invention, the method for producing the zirconia composite pre-sintered body by the immersion method of the present invention, the method for producing the zirconia composite pre-sintered body by the prior addition method of the present invention, and the method for producing a dental zirconia ceramic prosthesis will be described in detail below.

[0023] In this specification, unless otherwise specified, the expression "x to y" using numerical values ​​x and y means "greater than or equal to x and less than or equal to y." In such an expression, when a unit is assigned only to the numerical value y, the unit is also applied to the numerical value x.

[0024] 1. Method for producing zirconia composite ceramic of the present invention The method for producing a zirconia composite ceramic of the present invention has a major feature in that a composite zirconia pre-sintered body having a main structure consisting of a pre-sintered body of zirconium oxide that will become stabilized zirconia or partially stabilized zirconia and containing a predetermined amount of silicon dioxide or a precursor thereof is prepared (pre-sintered body preparation step), which is then sintered (sintering step), and then cooled according to a predetermined cooling profile (cooling step). Each of the above steps will be described in detail below.

[0025] 1-1.Preparation process of pre-sintered body In the preliminary sintered body preparation step, a composite zirconia preliminary sintered body is produced, which contains 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, 0.005 to 0.3 parts by mass of an aluminum oxide additive, and 0.05 to 5.0 parts by mass of silicon dioxide or a precursor thereof (however, the parts by mass of the silicon dioxide precursor represent parts by mass converted into silicon dioxide), and which contains the preliminary sintered body of zirconium oxide as a main structure.

[0026] The composite zirconia pre-sintered body prepared in the pre-sintered body preparation step is not particularly limited as long as it satisfies the above conditions, but it is preferably produced by the "immersion method" or the "pre-addition method".

[0027] That is, the preliminary sintered body preparation step is (A) a step of forming a first raw material composition containing a zirconia-based powder containing 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, and 0.005 to 0.3 parts by mass of an aluminum oxide additive into a predetermined shape, followed by pre-sintering at 600 to 1200°C to obtain a microporous pre-sintered body having a relative density of 45 to 65% and pores open to the outside (hereinafter also referred to as a "sorbing microporous pre-sintered body") (hereinafter also referred to as a "sorbing microporous pre-sintered body production step"); and The method includes a step of sorbing 0.05 to 5.0 parts by mass of silicon dioxide fine particles per 100 parts by mass of zirconium oxide into the pores of the microporous pre-sintered body obtained in the above step (hereinafter also referred to as the "sorption step"); Preparing a composite zirconia pre-sintered body in which fine particles of silicon dioxide are sorbed in the pores of the microporous pre-sintered body; or (B) a raw material composition preparation step of preparing a second raw material composition in which a zirconia-based powder containing 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, and 0.005 to 0.3 parts by mass of an aluminum oxide additive, and 0.05 to 5.0 parts by mass of a "silicon dioxide precursor" made of "amorphous silicon dioxide particles having an average primary particle size of 1 to 500 nm as measured by a dynamic light scattering method" and / or "a silicon dioxide source material made of a silicon-containing substance that can be converted into a silicon dioxide compound by sintering" are uniformly dispersed; a molding step of molding the second raw material composition to obtain a molded body having a predetermined shape; and A preliminary sintering step of preliminary sintering the compact at 600 to 1200 ° C.; It is preferable to prepare a composite zirconia pre-sintered body made of the pre-sintered body obtained in the pre-sintering step.

[0028] In short, in the method using the "immersion method" described above (A), a first raw material composition containing a zirconia-based powder is formed into a predetermined shape and then pre-sintered to obtain a sorbent microporous pre-sintered body, to which silicon dioxide microparticles are sorbed, thereby preparing a composite zirconia pre-sintered body in which the sorbent microporous pre-sintered body and the silicon dioxide microparticles are combined, whereas in the method using the "pre-addition method" described above (B), a second raw material composition containing a zirconia-based powder and a "silicon dioxide precursor" is formed into a predetermined shape and then pre-sintered to prepare a composite zirconia pre-sintered body. It is clear from the manufacturing method that the composite zirconia pre-sintered body prepared in (A) has a basic structure of a pre-sintered body of a zirconia-based powder, but the pre-sintering conditions in (B) are basically the same as those in (A), and the amount of "silicon dioxide precursor" contained in the second raw material composition is small. Therefore, it can be said that the composite zirconia pre-sintered body prepared in (B) also has a basic structure of a pre-sintered body of a zirconia-based powder.

[0029] In light of these commonalities, the following points will be first explained regarding (A) and (B) above. The zirconia-based powder used in the first raw material composition and the second raw material composition can be any zirconia raw material powder that can be used in conventional zirconia mill blanks, without any particular limitations. It is preferable to use zirconium oxide particles (particles made of stabilized zirconia or partially stabilized zirconia) containing a stabilizer in solid solution and having tetragonal or mixed tetragonal and cubic crystallinity. Because of the low crystal phase transformation rate and the low grain growth rate due to sintering, it is preferable to use particles having an average crystallite size of 0.001 μm to 50 μm, particularly 0.003 μm to 20 μm. Furthermore, from the viewpoint of ease of handling of the powder, the average secondary particle size of the zirconium oxide powder in the zirconia-based powder is preferably 0.01 to 500 μm, particularly 0.05 to 100 μm. The average crystallite size is preferably 0.001 μm to 50 μm, particularly 0.003 μm to 20 μm, because this makes it difficult for phase transformation of the oxide crystals to occur and prevents excessive grain growth during sintering.

[0030] Furthermore, the blending amount of each component in the zirconia-based powder relative to 100 parts by mass of zirconium oxide is preferably 5.5 to 12 parts by mass for yttrium oxide and 0.05 to 0.1 part by mass for aluminum oxide additive.

[0031] The first raw material composition and the second raw material composition may contain a pigment. There are no particular limitations on the pigment, and known pigments can be used in any combination. For example, erbium oxide, cobalt oxide, iron oxide, etc. can be used. Furthermore, a material that is white before sintering but can be colored after sintering and used as a pigment can also be used. Furthermore, other components such as a binder, a fine filler, a light-blocking agent, and a fluorescent agent can be included. Whether or not a binder component is added can be appropriately selected depending on the molding method of the sintered body, etc. When a binder component is added, for example, an acrylic binder, an olefin binder, or a wax can be used.

[0032] The molding of each raw material composition in (A) and (B) is preferably carried out by forming the first or second raw material composition into a compression molded body or green body of a predetermined shape. The molding method is not particularly different from the molding method used to produce conventional zirconia mill blanks, and methods known as powder molding or green body molding, such as press molding, extrusion molding, injection molding, casting, tape casting, additive manufacturing, powder molding, and stereolithography, can be used without any particular restrictions. Multi-stage molding may also be performed. For example, the raw material powder may be uniaxially press-molded and then further subjected to CIP (cold isostatic pressing). Furthermore, in the molding process, multiple types of mixed powders may be stacked and molded.

[0033] The shape of the compression molded body or green body obtained in the molding process may be determined appropriately depending on the shape of the target object. For example, when producing a mill blank, a disk-shaped body (disk type) or a rectangular or approximately rectangular shape (block type) is generally used.

[0034] In the preliminary sintering step, the compression-molded or green compact obtained by the molding process is sintered at a temperature lower than that of the main sintering step, followed by debinding and calcination to obtain a microporous pre-sintered body. Here, the debinding step refers to a process for volatilizing or decomposing the moisture, solvent, binder, and other components contained in the compression-molded or green compact obtained by the molding process. The calcination step refers to a process for heating the metal oxide powder particles to induce molecular and atomic diffusion (adhesion and fusion) on their surfaces, converting them into a polycrystalline body and improving the strength of the resulting microporous pre-sintered body to a level that makes it easy to handle and process. The preliminary sintering temperature is typically 600°C to 1200°C. Temperatures lower than 600°C may not be strong enough to maintain their shape during the sorption step. Temperatures higher than 1200°C may result in a high density of the microporous pre-sintered body, preventing sufficient penetration of the sol and resulting in a low strength.

[0035] The degreasing and / or calcination treatment may be carried out by any conventionally known method without any particular limitations, and may be carried out continuously or in multiple stages. Furthermore, in order to efficiently remove organic substances, it is preferable to carry out the treatment in an oxygen-containing air atmosphere. The degreasing and / or calcination treatment may also be carried out continuously by a method using the same equipment as the preceding molding step, such as the SPS (Spark Plasma Sintering) method or the HP (Hot Press) method.

[0036] In the pre-sintering or pre-sintering steps (A) and (B), a pre-sintered body of zirconium oxide, specifically a pre-sintered body of a zirconia-based powder, is formed, which is the main structure of the composite zirconia pre-sintered body. This pre-sintered body of zirconium oxide (also a sorption microporous pre-sintered body) itself is a microporous pre-sintered body with a relative density of 45 to 65% and pores that open to the outside. In (B), because the raw material to be pre-sintered (second raw material composition) itself contains a small amount of "silicon dioxide precursor," the degree of microporosity and relative density vary slightly, but do not differ significantly from those of the sorption microporous pre-sintered body.

[0037] The relative density is the ratio of actual density to theoretical density (calculated as relative density = (actual density / theoretical density) × 100(%)) and can be adjusted by controlling the temperature and time of pre-sintering. If the relative density is outside the above range, it becomes difficult to obtain a zirconia composite pre-sintered body by the immersion method. Furthermore, if pre-sintering is performed to achieve this relative density, the pre-sintered body will usually be microporous, with pores open to the outside. The average pore diameter of these pores is usually within the range of 50 to 200 nm. Here, the average pore diameter refers to the median diameter determined from the pore volume distribution in the pore diameter range of 5 nm to 250 μm obtained by mercury intrusion porosimetry, i.e., measurement using a mercury porosimeter.

[0038] The theoretical density varies depending on the type and content of the stabilizer and the content of the aluminum oxide additive, and is 6.10 g / cm, which is the theoretical density of tetragonal zirconia. 3As the content of these compounds increases, the density tends to decrease slightly. For example, Table 1 of Patent Document 1 shows the theoretical density of zirconia containing yttria and alumina, which is reproduced below for reference.

[0039] [Table 1]

[0040] The above has explained the common points between (A) and (B), but (A) and (B) differ in the method of compounding with silicon dioxide or its precursor. Therefore, the sorption step of (A) and the raw material composition preparation step of (B), which are the differences, will be explained below.

[0041] In the sorption step (A), 0.05 to 5.0 parts by mass of silicon dioxide particles are sorbed into the pores of the microporous pre-sintered body obtained by pre-sintering, per 100 parts by mass of zirconium oxide. The microporous pre-sintered body may be a newly prepared one according to the method described above, but a commercially available conventional zirconia mill blank for use as a cut member may also be used as the sorption microporous pre-sintered body, as long as the zirconia pre-sintered body contains the stabilizer made of yttrium oxide and aluminum oxide in amounts that satisfy the above-mentioned ranges and has a relative density that is measured by the Archimedes method or the like and has a value within the above-mentioned range.

[0042] The method for sorbing silicon dioxide particles into the pores of the microporous sintered body in the sorption step is not particularly limited as long as it is a method that sorbs silicon dioxide particles into the pores of the microporous sintered body, but a preferred method is to immerse the microporous sintered body in a sol in which silicon dioxide particles are dispersed in a dispersion medium (hereinafter also referred to as "silicon dioxide sol") for a certain period of time, and then remove the dispersion medium.

[0043] The silicon dioxide sol is not particularly limited as long as it is a liquid in which silicon dioxide is dispersed as the main component, but from the viewpoint of impregnating the pores of the microporous pre-sintered body, a silicon dioxide sol in which silicon dioxide fine particles are dispersed in a dispersion medium with a viscosity of 0.05 Pa s or less is preferred, and a silicon dioxide sol using water or alcohol as the dispersion medium is particularly preferred. Here, the term "main component" means a component that comprises 80 mass% or more of the total mass of oxides dispersed in the silicon dioxide sol.

[0044] In the silicon dioxide sol, the concentration of silicon dioxide dispersed in the silicon dioxide sol is preferably 0.03 to 0.9% by mass, more preferably 0.05 to 0.5% by mass. If the silicon dioxide concentration is lower than 0.03% by mass, the dental sintered body may not have sufficient strength after sintering, while if it is higher than 0.9% by mass, the transparency may decrease due to the difference in refractive index with zirconium oxide, the strength of the silicon dioxide may be too low to achieve a sufficient strength for a dental sintered body, and further, aggregation of silicon dioxide may occur, preventing the silicon dioxide from penetrating into the fine pores between the primary particles.

[0045] Furthermore, the silicon dioxide microparticles contained as the main component in the silicon dioxide sol must necessarily be of a size that can enter the pores of the microporous pre-sintered body, and the average primary particle diameter is preferably smaller than the average pore diameter of the microporous pre-sintered body measured by mercury intrusion porosimetry, and it is preferable that this condition is satisfied and that the particle diameter is 2 to 100 nm, particularly 10 to 30 nm. If the primary particle diameter of the silicon dioxide microparticles is smaller than 2 nm, it is difficult to maintain a highly dispersed state, and aggregation may occur during the sorption step. If the primary particle diameter is 100 nm or more, the silicon dioxide microparticles may not be able to penetrate deep into the microporous pre-sintered body, and sufficient strength as a dental sintered body may not be obtained.

[0046] The primary particle size of silicon dioxide microparticles is a value determined by nitrogen adsorption, i.e., it refers to the average particle size calculated based on the specific surface area S of the dried powder obtained by drying the medium, which is determined by nitrogen adsorption, and the density of the silicon dioxide.

[0047] The silicon dioxide sol may contain additives such as binders, dispersants, emulsifiers, pH adjusters, etc. to prevent the settling of the silicon dioxide microparticles, and these additives may be used alone or in combination of two or more.

[0048] Examples of binders include polyvinyl alcohol, polyvinylpyrrolidone, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, ethyl cellulose, polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0049] Examples of dispersants include ammonium polycarboxylate, ammonium polyacrylate, acrylic copolymer resin, acrylic acid ester copolymer, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants, nonionic surfactants, oleic glyceride, amine surfactants, and oligosaccharide alcohols.

[0050] Examples of emulsifiers include alkyl ethers, phenyl ethers, sorbitan derivatives, and ammonium salts.

[0051] Examples of pH adjusters include ammonia, ammonium salts, alkali metal salts, and alkaline earth metal salts.

[0052] Furthermore, the silicon dioxide sol may contain a coloring component or a fluorescence-imparting component for zirconia. The coloring component may be iron ions or cobalt ions, and the fluorescence-imparting component may be bismuth ions or neodymium ions.

[0053] The method for immersing the microporous pre-sintered body in the silicon dioxide sol for a certain period of time is not particularly limited as long as the method allows the silicon dioxide sol to penetrate into the pores of the microporous pre-sintered body, and may be under reduced pressure, normal pressure, or increased pressure. The immersion time can also be freely selected as long as the silicon dioxide sol is sufficiently penetrated into the pores of the microporous pre-sintered body. The immersion temperature can also be freely selected as long as the silicon dioxide sol is sufficiently penetrated into the pores of the microporous pre-sintered body, but is preferably a temperature lower than the boiling point of the dispersion medium of the silicon dioxide sol.

[0054] The method for removing the dispersion medium is not particularly limited as long as it can remove the solvent from the silicon dioxide sol, but it is preferable to use a vacuum drying method and / or a heat drying method, as they allow for easy removal of the solvent while maintaining the shape of the microporous pre-sintered body. Here, the vacuum drying method is a method for removing the dispersion medium under reduced pressure, for example, at 800 hectopascals or less, and the heat drying method is a method for removing the dispersion medium at a temperature above room temperature, and by heating under reduced pressure, the dispersion medium can be removed (dried) at a temperature lower than the boiling point of the dispersion medium.

[0055] Furthermore, the calcination treatment may be carried out again together with the drying step, or may be carried out simultaneously or in multiple stages.

[0056] Next, the raw material composition preparation step (B) will be described. In this raw material composition preparation step, a raw material composition is prepared in which the zirconia-based powder and 0.05 to 5.0 parts by mass of a silicon dioxide precursor composed of amorphous silicon dioxide particles having an average primary particle size of 1 to 500 nm as measured by dynamic light scattering and / or a silicon dioxide source material composed of a silicon-containing substance that can be converted into a silicon dioxide compound by sintering are uniformly dispersed.

[0057] When amorphous silicon dioxide particles are used, from the viewpoint of effectiveness, it is preferable that the amorphous silicon dioxide particles are nano-crystalline silicon dioxide particles having an average primary particle diameter of 5 to 100 nm, particularly 5 to 50 nm, as measured by dynamic light scattering (for example, using an ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd. as a measuring device and water as a dispersion medium).

[0058] When using the silicon-containing substance as a silicon dioxide precursor, the silicon-containing substance is not particularly limited as long as it can be converted into a silicon dioxide compound by sintering, and inorganic or organic silicon compounds can be used. From the viewpoint of easy conversion into a silicon dioxide compound by sintering, it is preferable to use an organosilicon compound. As such an organosilicon compound, an organosilicon compound having an Si—O bond and having a molecular weight of 500 or less calculated as one silicon molecule is preferred. Examples of suitable organosilicon compounds include tetraethoxysilane, tetramethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, triethylsiloxane, hexamethylcyclotrisiloxane, and silicone oil. Due to their high silicon content, it is particularly preferred to use tetraethoxysilane and / or tetramethoxysilane.

[0059] The content of the amorphous silicon dioxide particles and / or the silicon dioxide precursor (hereinafter also collectively referred to as "silicon dioxide precursor, etc.") contained in the zirconia composite pre-sintered body obtained in (B) should be 0.05 to 5.0 mass% in terms of silicon dioxide, based on the mass of the zirconia composite pre-sintered body, and more preferably 0.09 to 1.5 mass%. If the content of the silicon dioxide source material is less than 0.05 mass% in terms of silicon dioxide, the sintered body may not have sufficient strength for dental use after sintering. If it is more than 5.0 mass%, the transparency may decrease due to the difference in refractive index with zirconium oxide, or the strength of silicon dioxide may be low and the sintered body may not have sufficient strength for dental use.

[0060] The method for mixing the zirconia-based powder with the silicon dioxide precursor, etc. is not particularly limited as long as it is a method that can prepare a raw material composition in which the zirconia-based powder and the silicon dioxide precursor, etc. are uniformly dispersed. However, wet preparation is preferred, in which the zirconia-based powder and the silicon dioxide precursor, etc. are mixed in the presence of a dispersion medium to prepare the raw material composition, and the dispersion medium is then removed from the resulting raw material composition containing the dispersion medium.

[0061] A preferred method for mixing the zirconia-based powder with the silicon dioxide precursor or the like is to mix a slurry or dispersion in which the zirconia-based powder is dispersed in a dispersion medium with a solution of an organosilicon compound and / or a sol in which the nano-silicon dioxide particles are dispersed in a dispersion medium. The dispersion medium used in the wet preparation is not limited as long as it is a solvent in which the silicon dioxide precursor or the like can be dispersed or dissolved. For example, known dispersion media such as water, alcohols (e.g., ethanol), and acetone can be used. However, from the viewpoints of safety and ease of solvent removal, water or alcohols are preferred. Furthermore, because the raw material composition can be easily handled during the molding process, a mixing method that does not disrupt the secondary particles of the zirconia-based powder during preparation is more preferred. Specifically, methods such as wet stirring, shaking, vibration, and ultrasonic waves can be used, but wet stirring and shaking are more preferred.

[0062] The method for removing the dispersion medium from a raw material composition containing the dispersion medium is not particularly limited as long as it can remove the dispersion medium. However, from the viewpoints of short solvent removal time and ability to remove almost all of the solvent, it is preferable to adopt a vacuum drying method and / or a heat drying method. Here, the vacuum drying method is a method for removing the solvent under reduced pressure, for example, at 800 hectopascals or less, and the heat drying method is a method for removing the solvent at a temperature above room temperature. By heating under reduced pressure, the organic solvent can be removed (dried) at a temperature below the boiling point of the organic solvent. Even when the heat drying method is adopted, from the viewpoint of not requiring treatment at high temperatures, it is preferable to dry at a temperature below 100°C, for example, by combining it with a vacuum drying method. Furthermore, granulation may be performed simultaneously with drying using a spray dryer or the like.

[0063] 1-2.Sintering process In the sintering step, the composite zirconia pre-sintered body prepared in the pre-sintered body preparation step is sintered at a temperature of 1250 to 1800°C.

[0064] The main sintering is preferably carried out at a temperature of 1300° C. or higher and 1700° C. or lower, more preferably 1400° C. or higher and 1600° C. If the main sintering temperature is 1250° C. or lower, sufficient sintered density, translucency, and strength may not be obtained, and if the sintering temperature is higher than 1800° C., the grain growth of zirconium oxide may proceed too quickly, making it impossible to obtain sufficient strength.

[0065] As the sintering method, any conventionally known method can be used without any particular limitation, and the holding time at the sintering temperature is preferably 30 minutes to 4 hours.

[0066] 1-3. Cooling process The cooling process includes a first cooling process in which the sintered body sintered in the sintering process is cooled at a cooling rate of 100 to 900 (°C / hour) {=1.7 to 15.0°C / min} to a primary cooling temperature, which is a predetermined temperature selected from the range of 400 to 900°C, and a second cooling process in which the sintered body cooled to the primary cooling temperature in the first cooling process is cooled at a cooling rate of 1000 to 9000 (°C / hour) {=17.0 to 150.0°C / min} to a temperature of 50°C or less.

[0067] (1) First cooling process In the first cooling step, the sintered body sintered in the sintering step is cooled at a cooling rate of 100 to 900 (°C / hour) until it reaches a primary cooling temperature, which is a predetermined temperature selected from the range of 400 to 900°C. Here, the cooling rate refers to an average cooling rate obtained by dividing the difference (°C) between the temperature of the sintered body (heating temperature) when heating is stopped in the sintering step and the primary cooling temperature by the time (hours) from when heating in the sintering step is stopped until the temperature reaches the primary cooling temperature.

[0068] The method of the first cooling is not particularly limited as long as it satisfies the above conditions, but since the high temperature conditions are involved, and taking safety into consideration, a method of cooling in a sintering furnace is preferred.

[0069] The cooling rate in the first cooling step is preferably 350 to 800°C / hour, and more preferably 450 to 750°C / hour. If the cooling rate is slower than 100°C / hour, the compressive stress expected to be applied to the sintered body may be removed by heat, resulting in insufficient strength improvement, and the cooling process may take a very long time. If the cooling rate is faster than 900°C / hour, the sintered body, sintering plate, and other components may be unable to withstand the thermal history due to extremely rapid cooling in the second cooling step, resulting in damage.

[0070] The primary cooling temperature in the first cooling step is preferably 400 to 750° C., and more preferably 400 to 550° C. If the primary cooling temperature is lower than 400° C., the silicon dioxide does not become low-density silicon dioxide glass, and the inherent compressive stress is insufficient, which may result in a failure to achieve a sufficient strength improvement effect.If the primary cooling temperature is higher than 900° C., various components such as the sintered body and sintered plate may not be able to withstand the thermal history due to extremely rapid cooling in the second cooling step, and may be damaged.

[0071] (2)Second cooling process In the second cooling step, the sintered body cooled to the primary cooling temperature in the first cooling step is cooled to 50°C or less at a cooling rate of 1000 to 9000 (°C / hour). Here, the cooling rate refers to an average cooling rate obtained by dividing the difference (°C) obtained by subtracting 50°C from the primary cooling temperature by the time (hours) required for the temperature to reach 50°C after the primary cooling temperature is reached.

[0072] The method of the second cooling is not particularly limited as long as it satisfies the above conditions. However, since the temperature inside the sintering furnace is high and it is difficult to increase the cooling rate inside the sintering furnace, it is preferable to remove the sintered body from the sintering furnace and cool it in the air at room temperature.

[0073] The cooling rate in the second cooling step is preferably 1000 to 3000°C / hour, and more preferably 1200 to 2500°C / hour. If the cooling rate is slower than 1000°C / hour, the compressive stress expected to be applied to the sintered body may be removed by heat, and sufficient strength improvement may not be achieved. If the cooling rate is faster than 9000°C / hour, various components such as the sintered body and sintering plate may not be able to withstand the thermal history due to extremely rapid cooling, and may be damaged.

[0074] 2. Manufacturing method for dental zirconia prostheses The method for producing a dental zirconia prosthesis of the present invention is characterized by the following: A zirconia mill blank is used as the zirconia mill blank, which has a cutting portion made of a composite zirconia pre-sintered body prepared in the pre-sintered body preparation step of the "method for producing a zirconia composite ceramic of the present invention." Furthermore, the cooling process after the pre-sintering employs a cooling profile similar to that of the cooling process of the "method for producing a zirconia composite ceramic of the present invention." The resulting zirconia prosthesis is made of the zirconia composite ceramic obtained by the "method for producing a zirconia composite ceramic of the present invention." Therefore, the resulting zirconia prosthesis has higher strength than conventional zirconia prostheses. For example, the biaxial bending strength of the material constituting the zirconia prosthesis obtained by the method for producing a dental zirconia prosthesis of the present invention, as measured according to JIS T6526:2018, is as high as 800 to 2000 MPa, and can even be as high as 1100 to 2500 MPa. Therefore, the method for producing a dental zirconia prosthesis of the present invention is suitable as a method for producing prostheses that require high strength, such as long-span bridges.

[0075] A zirconia dental mill blank having a cutting portion made of the composite zirconia pre-sintered body is essentially the same as a zirconia mill blank, except that the cutting portion is made of the composite zirconia pre-sintered body. For example, the cutting portion is preferably a (solid) block formed into a cylindrical shape or a (solid) disk formed into a plate or board shape, and may have a holder for attaching it to a cutting machine, as needed. Furthermore, the zirconia mill blank can be cut using a CAD / CAM system to obtain a semi-finished product having a shape corresponding to the shape of the desired dental prosthesis, as in conventional methods. Furthermore, after cutting using a CAD / CAM system, the resulting semi-finished product may be further modified in shape using a dental laboratory engine or the like, or the surface may be polished. If necessary, the color tone may be adjusted using a penetrating colorant or a clarifying liquid. [Example]

[0076] The present invention will be specifically described below with reference to examples and comparative examples, although the present invention is not limited to these examples.

[0077] First, the raw materials used in each example and comparative example and their abbreviations and symbols will be explained.

[0078] 1. Zirconia-based powder ZpexSmile: Zirconium oxide manufactured by Tosoh Corporation, aluminum oxide content 0.05% by mass, yttrium oxide content 9.3% by mass, theoretical density: 6.050 g / cm 3 Zpex4: Zirconium oxide manufactured by Tosoh Corporation, aluminum oxide content 0.05 mass%, yttrium oxide content 6.9 mass%, theoretical density: 6.078 g / cm 3 Zpex: Zirconium oxide manufactured by Tosoh Corporation, aluminum oxide content 0.05 mass%, yttrium oxide content 5.3 mass%, theoretical density: 6.093 g / cm 3 TZ-8YSB: Zirconium oxide manufactured by Tosoh Corporation, aluminum oxide content 0.005% by mass or less (below the detection limit), yttrium oxide content 13.74% by mass, theoretical density: 6.011 g / cm 3 .

[0079] 2. Silicon dioxide sol LUDOX-LS: Silicon dioxide sol manufactured by Sigma-Aldrich, content 30 mass percent, primary particle size 12 nm, dispersion medium water LUDOX-SM: Silicon dioxide sol manufactured by Sigma-Aldrich, content 30 mass percent, primary particle size 7 nm, dispersion medium water.

[0080] 3. Silicon dioxide precursors, etc. LUDOX-LS: Silicon dioxide sol manufactured by Sigma-Aldrich, content 30 mass percent, primary particle size 12 nm, dispersion medium water TEOS: Tetraethoxysilane Si(OC2H5)4, manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight equivalent to one silicon molecule: 208 g / mol.

[0081] 4.Dispersion medium Distilled water: Fujifilm Wako Pure Chemical Industries, Ltd. Ethanol: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0082] Example 1 (Example using composite zirconia pre-sintered body obtained by immersion method) (1) Preparation and evaluation of microporous presintered bodies for sorption 1.5 g of ZpexSmile (first raw material composition) was uniaxially pressed using a 20 mm diameter press die at a maximum load of 200 MPa to obtain a disk-shaped compact (thickness: 1.45 mm). The compact was then pre-sintered in a ring furnace at 1000°C for 30 minutes to obtain a microporous pre-sintered compact (thickness: 1.45 mm) that would become a sorption microporous pre-sintered compact. The density was calculated from the mass and volume of the obtained disk-shaped microporous pre-sintered compact, and the relative density was determined by dividing this by the theoretical sintered density, which was 49.8%.

[0083] Separately, a 5 mm thick disk-shaped microporous pre-sintered body was prepared in the same manner except for changing the amount of powder used to 6.5 g, and then cut into a 5 mm x 5 mm x 5 mm rectangular column to prepare a sample for measuring the average pore diameter. The average pore diameter was measured and found to be 103 nm. The average pore diameter was measured using a fully automatic multifunctional mercury porosimeter (Quantachrome's "POREMASTER") at a mercury surface tension of 480 erg / cm. 2 The test was performed at a contact angle of 140°, a discharge contact angle of 140°, and a pressure of 0 to 50,000 psia.

[0084] (2) Sorption process and evaluation of the resulting composite zirconia pre-sintered body A silicon dioxide sol was prepared by mixing 0.03 g of LUDOX-LS with 10 mL of ion-exchanged water. The sorbent microporous calcined body obtained in the manufacturing process of the sorbent microporous calcined body was immersed in the prepared silicon dioxide sol at room temperature and atmospheric pressure (25°C, 1 atm). After leaving it to stand for 1 hour, it was removed from the silicon dioxide sol and dried for 20 minutes on a hot stirrer set at 120°C to obtain a composite zirconia calcined body. A composite zirconia calcined body prepared separately in the same manner was analyzed using a field emission electron probe microanalyzer (FE-EPMA). Based on the results, the silicon dioxide content was determined to be 0.24% by mass.

[0085] (3) Sintering process, cooling process and evaluation of the resulting zirconia composite ceramics The obtained composite zirconia pre-sintered body was heated from room temperature to 1450°C in 3 hours in an electric furnace, then held at 1450°C for 2 hours, and then slowly cooled in the sintering furnace at 600°C / hour to the primary cooling temperature of 500°C. Once it reached 500°C, it was removed from the furnace and rapidly cooled to below 50°C at 1500°C / hour to obtain a zirconia composite ceramic. The biaxial bending strength and transparency of the obtained zirconia composite ceramic were evaluated as follows. The biaxial bending strength was 1065 MPa, and the contrast ratio: Yb / Yw was 0.648.

[0086] [Evaluation of biaxial bending strength] Measurements were carried out using a testing machine manufactured by Shimadzu Corporation in accordance with JIS T6526:2018, with a crosshead speed of 1.0 mm / min, a support circle diameter of 10 mm, and an indenter diameter of 1.4 mm. The biaxial bending strength was calculated using the following formula. δ=-0.2387×P×(XY) / b 2 X = (1 + ν) × ln[(r2 / r3) 2 ]+[(1-ν) / 2]×(r2 / r3) 2 Y=(1+ν)×[1+{ln(r1 / r3) 2}]+(1-ν)×(r1 / r3) 2 δ [MPa]: Biaxial bending strength P [N]: Test force b [mm]: test piece thickness ν: Poisson's ratio (0.31) r1 [mm]: Support circle radius r2[mm]:Indenter radius r3 [mm]: specimen radius.

[0087] [Transparency Assessment] The sintered body was polished to a thickness of 1 mm using waterproof abrasive paper #800, #1500, and #3000. Both sides were then mirror-polished using Superstar V (Nippon Dental Industries Co., Ltd.), an abrasive for porcelain, hybrid resin, and zirconia, to prepare a sample for transparency evaluation. Transparency was evaluated by measuring the spectral reflectance of the sample against a black and white background using a spectrophotometer (Tokyo Denshoku Corporation, Spectrophotometer "TC-1800MKII") and calculating the contrast ratio Yb / Yw, calculated by dividing the Y value (Yb) on the black background by the Y value (Yw) on the white background. The smaller the Yb / Yw ratio, the more transparent the sample.

[0088] Examples 2 to 7 and Comparative Examples 1 to 4 Microporous pre-sintered bodies, composite pre-sintered bodies of zirconia, and zirconia composite ceramics were produced in the same manner as in Example 1, except that the type of zirconia-based powder, the type and amount of silicon dioxide sol, and the cooling conditions were changed as shown in Tables 2 and 3, and evaluations were performed in the same manner as in Examples. The evaluation results are shown in Table 5. In Tables 2 and 3, "↑" means "same as above," and "cooling temperature" in the "primary cooling step" means "primary cooling temperature."

[0089] Example 8 (Example using composite zirconia pre-sintered body obtained by prior addition method) (1) Production and evaluation of composite zirconia pre-sintered body After weighing 30 g of ZpexSmile and 150 g of distilled water, 0.2 g of LUDOX-LS was added and mixed for 10 minutes using a stirrer. After that, the water was removed by reducing the pressure in an evaporator at 50°C, and a raw material composition powder (second raw material composition) was obtained.

[0090] 1.5 g of the obtained raw material composition powder was uniaxially pressed using a press die with a diameter of 20 mm at a maximum load of 200 MPa to obtain a disk-shaped molded body (thickness: 1.45 mm). The molded body was then pre-sintered using a ring furnace at 1000°C for 30 minutes to obtain a pre-sintered composite zirconia body (thickness: 1.45 mm). A pre-sintered composite zirconia separately prepared in the same manner was analyzed using an X-ray fluorescence analyzer (XRF), and the content of the silicon dioxide source material in terms of silicon dioxide was calculated based on the results and was found to be 0.21% by mass.

[0091] (2) Sintering process, cooling process and evaluation of the resulting zirconia composite ceramics The resulting composite zirconia pre-sintered body was sintered to obtain a zirconia composite ceramic in the same manner as in Example 1. The biaxial bending strength of the resulting zirconia composite ceramic was evaluated, and the biaxial bending strength was found to be 1044 MPa.

[0092] Examples 9 to 10 and Comparative Examples 5 to 7 Except for changing the type of zirconia-based powder, the type and blending amount of silicon dioxide precursor, the type of dispersion medium, and the cooling conditions as shown in Tables 6 and 7, composite zirconia pre-sintered bodies and zirconia composite ceramics were produced in the same manner as in Example 8, and evaluated in the same manner as in Example 8. The evaluation results are shown in Table 8.

[0093] As can be seen from the results of Examples 1 to 10, when zirconia composite ceramics are produced using a method satisfying the conditions specified in the present invention, sintered bodies with high strength are obtained, and the biaxial bending strength is improved by 15% or more compared to conventional zirconia sintered bodies containing the same amount of yttrium oxide stabilizer and aluminum oxide additive. In contrast, in Comparative Examples 1, 2, and 5, in which the primary cooling temperature is below the specified lower limit, and in Comparative Example 3, in which the cooling rate in the primary cooling step is below the specified lower limit, the biaxial bending strength of the sintered bodies tends to be slightly improved compared to conventional zirconia sintered bodies containing the same amount of yttrium oxide stabilizer and aluminum oxide additive, but the strength improvement is less than 15%. Furthermore, in Comparative Example 4, in which the aluminum oxide content is below the specified lower limit, no improvement in biaxial bending strength is observed. Furthermore, in Comparative Example 6, in which the silicon dioxide content was greater than the upper limit specified in the present invention, the silicon dioxide formed a brittle layer, resulting in a decrease in biaxial bending strength. On the other hand, in Comparative Example 7, in which the silicon dioxide content was less than the lower limit specified in the present invention, the silicon dioxide content was so low that a sufficient strength improvement effect was not obtained.

[0094] Reference Examples 1 to 5 (Examples of producing a conventional zirconia sintered body using a conventional pre-sintered body not compounded with a silicon dioxide component) In Reference Example 1, a composite zirconia pre-sintered body and a zirconia composite ceramic were obtained in the same manner as in Example 1, except that immersion was performed using 10 mL of ion-exchanged water containing no silicon dioxide instead of silicon dioxide sol. In Reference Examples 2 to 5, a composite zirconia pre-sintered body and a zirconia composite ceramic were produced in the same manner as in Reference Example 1, except that the type of zirconia-based powder and cooling conditions were changed as shown in Table 4. Note that the zirconia-based powder, pre-sintering conditions, main sintering conditions, and cooling conditions were the same for Reference Example 1 as in Example 1, for Reference Example 2 as in Comparative Example 2, and for Reference Examples 3 and 4 as in Examples 6 and 7, respectively. The evaluation results of the obtained composite zirconia pre-sintered bodies and zirconia composite ceramics are shown in Table 5.

[0095] As shown in Table 5, the biaxial bending strength of the sintered bodies obtained in Examples 1, 6, and 7 was improved by 15% or more. Furthermore, as is clear from a comparison between Reference Examples 1 and 2, when silicon dioxide was not contained, no improvement in biaxial bending strength was observed even when the cooling conditions of the present invention were used.

[0096] [Table 2]

[0097] [Table 3]

[0098] [Table 4]

[0099] [Table 5]

[0100] [Table 6]

[0101]

Table 7

[0102]

Table 8

Claims

1. a preliminary sintered body preparation step of preparing a composite zirconia preliminary sintered body, the composite zirconia preliminary sintered body containing 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, 0.005 to 0.3 parts by mass of an aluminum oxide additive, and 0.05 to 5.0 parts by mass of silicon dioxide or a precursor thereof (however, the parts by mass of the silicon dioxide precursor represent parts by mass converted into silicon dioxide), and containing the preliminary sintered body of zirconium oxide as a main structure; a sintering step of sintering the composite zirconia pre-sintered body prepared in the pre-sintered body preparation step at a temperature of 1250 to 1800°C; and A method for producing zirconia-based ceramics, comprising a cooling step of cooling the sintered body sintered in the sintering step, The cooling step includes a first cooling step of cooling the sintered body at a cooling rate of 100 to 900 (°C / hour) to a primary cooling temperature, which is a predetermined temperature selected from a range of 400 to 900°C, and a second cooling step of cooling the sintered body cooled to the primary cooling temperature in the first cooling step at a cooling rate of 1000 to 9000 (°C / hour) to a temperature of 50°C or less. A method for producing a zirconia composite ceramic.

2. The preliminary sintered body preparation step (A) forming a first raw material composition containing a zirconia-based powder containing 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, and 0.005 to 0.3 parts by mass of an aluminum oxide additive into a predetermined shape, and then calcining the resulting material at 600 to 1200°C to obtain a microporous calcined body having a relative density of 45 to 65% and pores that are open to the outside; and sorbing 0.05 to 5.0 parts by mass of silicon dioxide fine particles relative to 100 parts by mass of zirconium oxide into the pores of the microporous pre-sintered body obtained in the above step; A step of preparing a composite zirconia pre-sintered body in which fine particles of silicon dioxide are sorbed in the pores of the microporous pre-sintered body; or (B) a raw material composition preparation step of preparing a second raw material composition in which a zirconia-based powder containing 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, and 0.005 to 0.3 parts by mass of an aluminum oxide additive, and 0.05 to 5.0 parts by mass of a "silicon dioxide precursor" made of "amorphous silicon dioxide particles having an average primary particle size of 1 to 500 nm as measured by a dynamic light scattering method" and / or "a silicon dioxide source material made of a silicon-containing substance that can be converted into a silicon dioxide compound by sintering" are uniformly dispersed; a molding step of molding the second raw material composition to obtain a molded body having a predetermined shape; and A preliminary sintering step of preliminary sintering the compact at 600 to 1200 ° C.; A step of preparing a composite zirconia pre-sintered body made of the pre-sintered body obtained in the pre-sintering step, A method for producing the zirconia composite pre-sintered body according to claim 1.

3. a cutting process for obtaining a semi-finished product having a shape corresponding to the shape of a desired dental prosthesis by cutting a zirconia dental mill blank having a cutting portion made of a composite zirconia pre-sintered body, the cutting portion comprising 100 parts by mass of zirconium oxide, 4 to 14 parts by mass of a stabilizer made of yttrium oxide, 0.005 to 0.3 parts by mass of an aluminum oxide additive, and 0.05 to 5.0 parts by mass of silicon dioxide or a precursor thereof (however, the parts by mass of the silicon dioxide precursor represent parts by mass converted into silicon dioxide), and the composite zirconia pre-sintered body contains the zirconium oxide pre-sintered body as a main structure, using a CAD / CAM system; sintering the semi-finished product obtained in the above step at a temperature of 1250 to 1800°C; and A method for producing a dental zirconia ceramic prosthesis, comprising a cooling step of cooling the sintered body obtained in the sintering step, The cooling step includes a first cooling step of cooling the sintered body at a cooling rate of 100 to 900 (°C / hour) to a primary cooling temperature, which is a predetermined temperature selected from a range of 400 to 900°C, and a second cooling step of cooling the sintered body cooled to the primary cooling temperature in the first cooling step at a cooling rate of 1000 to 9000 (°C / hour) to a temperature of 50°C or less. A method for producing a dental zirconia ceramic prosthesis, comprising:

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