Method for manufacturing oxide ceramic molded body

Abstract

The present invention provides an oxide-ceramic molded body manufacturing method using an oxide-ceramic powder having a nano-order average primary particle size (in particular, 120 nm or less), and being able to manufacture a molded body with a high production yield in a simple manner. The present invention relates to a method for manufacturing an oxide-ceramic molded body, in which method a powder containing oxide-ceramic particles having an average primary particle size of 1 to 120 nm is press-molded under a reduced pressure. The press molding is preferably carried out under a reduced pressure of 0.1 to 100 kPa or less.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an oxide ceramic formed body. [Background technology]

[0002] Oxide ceramics are widely used industrially. In particular, zirconia sintered bodies have recently been used as dental materials, such as dental prostheses. These dental prostheses are often produced by forming a zirconia molded body having a desired shape, such as a disk or a prism, by pressing zirconia particles or by molding a composition containing zirconia particles, and then calcining this to form a calcined body (mill blank). This is then milled into the shape of the desired dental prosthesis and further sintered.

[0003] There are cases where a zirconia sintered body is required to have both high translucency and high strength. Methods for solving such problems have been proposed, for example, in Patent Documents 1 and 2. Patent Document 1 discloses a method for producing a zirconia molded body, which can easily and efficiently produce a zirconia sintered body that has excellent quality, including both high translucency and high strength.

[0004] Specifically, Patent Document 1 discloses a method for producing a zirconia molded body, which includes a step of humidifying a wet preform containing zirconia particles to form a wet molded body, and a step of pressurizing the wet molded body. It also discloses that the average primary particle diameter of the zirconia particles is preferably 30 nm or less, that the wet preform is preferably obtained by press-molding a powder containing zirconia particles, and that the powder containing zirconia particles is preferably obtained by drying a slurry containing zirconia particles.

[0005] Patent Document 2 also discloses nanocrystalline zirconia and a method for processing the same. Specifically, the dental zirconia ceramic exhibits opalescence, has a grain size in the range of 10 nm to 300 nm, a density of at least 99.5% of theoretical density, a visible light transmittance of 45% or more at 560 nm, and a strength of at least 800 MPa. The dental zirconia ceramic is made by a method including the steps of: providing a zirconia green blank having zirconia nanoparticles with an average grain size of less than 20 nm; molding the zirconia green blank by CAD / CAM, low-pressure injection molding (LPIM), or hot pressing; or heating the zirconia green blank to form a brown blank and molding the brown blank by CAD / CAM machining; and sintering the molded zirconia green blank or brown blank at 1200°C or less to provide an opalescent sintered zirconia body. Patent Document 2 also discloses a method for producing opalescent zirconia dental products, in which the step of forming the suspension into a blank or dental product includes centrifugal casting, drop casting, gel casting, injection molding, slip casting, squeeze filtration, and / or electrophoretic deposition (EPD). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-1973 [Patent Document 2] Japanese Patent Application Publication No. 2019-5627 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in Patent Document 1, the objective is to reduce chipping and cracking of the zirconia sintered body that is finally produced by press-molding a powder to obtain a wet preform, humidifying the wet preform to obtain a wet preform, and then using a molded body that is pressurized after the wet preform is obtained, and the production yield when producing the wet preform was not considered. In the method of press-molding powder as described in Patent Document 1, when molding powder having a nano-sized particle size (120 nm or less) with a small average primary particle size, it is sometimes difficult to form a pressed compact because the specific surface area increases. Although molding is possible with Patent Document 1, the inventors have found that when a uniaxial press is used, there are problems such as air remaining inside the pressed compact causing chips or cracks in the pressed compact when it is removed from the mold, making it difficult to obtain press-molded bodies with a good yield.

[0008] Furthermore, the present inventors have found that even if a green body can be judged to have been formed by visual inspection, the small amount of air remaining inside the green body can affect the green body during subsequent calcination, causing cracks to form in the green body and reducing the yield in the production of the calcined body.Furthermore, in a method for producing a zirconia green body in which a pressure treatment such as cold isostatic pressing (CIP) is performed instead of uniaxial pressing, it is difficult to remove the air when a powder with a small particle size is used, and this can result in a decrease in the quality of the green body and a decrease in production yield.

[0009] Furthermore, the centrifugal casting method for a slurry of powder with nano-sized particle diameters, as described in Patent Document 2, has the problem that the separation of the powder (solid) from the liquid is poor due to the large specific surface area of ​​the nanoparticles, which requires a great deal of time and is unsuitable for industrial production. Furthermore, when the gel casting method is used, if the particle diameter is small, the particles are likely to clog the filter, which requires a long time to separate the particles from the liquid and requires frequent filter replacement to remove the clogs, making it extremely inefficient from an industrial standpoint. Furthermore, Patent Document 2 did not consider the production yield when producing a molded body (green body).

[0010] Patent Documents 1 and 2 did not consider the production yield when molding an oxide ceramic powder having an average primary particle size of nano-size (particularly, 120 nm or less). However, when molding an oxide ceramic powder having an average primary particle size of 120 nm or less, problems such as chipping or cracking of the molded body due to the air remaining inside the molded body due to the particle size being too small, as described above, have been found. Furthermore, even if the molded body appears to have no problems when visually inspected, cracks may occur during calcination due to the influence of trace amounts of air remaining inside the molded body. This problem is particularly noticeable when manufacturing molded bodies having a thickness of 10 mm or more.

[0011] Therefore, an object of the present invention is to provide a method for producing an oxide ceramic molded body, which can produce a molded body with a high production yield using an oxide ceramic powder having an average primary particle size of nano-size (particularly 120 nm or less). [Means for solving the problem]

[0012] As a result of extensive research into solving the above problems, the inventors have found that when powder having a small average primary particle size is press-molded using a press molding machine, carrying out the press molding under reduced pressure significantly reduces chipping or cracking in the molded body. As a result of further research, they have completed the present invention.

[0013] That is, the present invention includes the following inventions. [1] A method for producing an oxide ceramic compact, comprising press-molding, under reduced pressure, a powder containing oxide ceramic particles having an average primary particle size of 1 to 120 nm. [2] The method for producing an oxide ceramic formed body according to [1], wherein the press forming is carried out under a reduced pressure of 0.1 kPa or more and 100 kPa or less. [3] The method for producing an oxide ceramic formed body according to [1] or [2], wherein the load pressure in the press molding is 10 MPa or more and 200 MPa or less. [4] The method for producing an oxide ceramic formed body according to any one of [1] to [3], wherein the powder containing oxide ceramic particles is a powder containing zirconia particles and / or a powder containing alumina particles. [5] The method for producing an oxide ceramic formed body according to [4], wherein the powder containing the oxide ceramic particles further contains a stabilizer capable of suppressing the phase transition of zirconia. [6] The powder containing oxide ceramic particles is a powder containing zirconia particles, The method for producing an oxide ceramic formed body according to [5], wherein the stabilizer is yttria. [7] The method for producing an oxide ceramic formed body according to [6], wherein the content of the yttria is 2.0 mol % or more and 9.0 mol % or less based on the total number of moles of zirconia and yttria. [8] A method for producing a calcined oxide ceramic body, which comprises calcining the molded body obtained by the method for producing an oxide ceramic molded body according to any one of [1] to [7]. [9] The method for producing a calcined oxide ceramic body according to [8], wherein the calcination temperature is 300°C or higher and lower than 1100°C.

[10] The method for producing a calcined oxide ceramic body according to [8] or [9], wherein the oxide ceramic molded body is a zirconia molded body or an alumina molded body.

[11] A method for producing an oxide ceramic sintered body, comprising sintering an oxide ceramic molded body obtained by the method for producing an oxide ceramic molded body according to any one of [1] to [7], or an oxide ceramic calcined body obtained by the method for producing an oxide ceramic calcined body according to any one of [8] to

[10] .

[12] The method for producing an oxide ceramic sintered body according to

[11] , wherein the sintering temperature is 900°C or higher and 1500°C or lower. [Effects of the Invention]

[0014] According to the present invention, there can be provided a method for producing an oxide ceramic formed body, which can produce a formed body with a high production yield using an oxide ceramic powder having an average primary particle size of nano-size (particularly 120 nm or less). According to the present invention, when a material having an average primary particle size of nano-sized (particularly 120 nm or less) is pressed using a press molding machine, the pressing is carried out under reduced pressure, thereby reducing the amount of air remaining in the pressed body and improving the yield of the press molding itself, thereby providing a method for producing an oxide ceramic molded body. Furthermore, the present invention provides a method for producing an oxide ceramic molded body, which does not require special equipment or complicated processes, and which can produce a molded body with a high production yield using an oxide ceramic powder having an average primary particle size in a simple manner. Furthermore, the oxide ceramic molded body obtained by this method has fewer chips or cracks during calcination and sintering, making it possible to easily produce calcined bodies (semi-sintered bodies) or sintered bodies with a thickness of 10 mm or more.In addition, the formation of microvoids in the sintered body is reduced, resulting in improved translucency. In particular, when zirconia particles are used, the present invention makes it possible to easily produce, with a high production yield, a zirconia molded body and a zirconia calcined body for easily producing, with a high production yield, a zirconia sintered body having excellent translucency and strength. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described, but the following description does not limit the present invention.

[0016] [Method for producing oxide ceramic molded body] The method for producing an oxide ceramic formed body of the present invention includes a step of press-molding, under reduced pressure, a powder containing oxide ceramic particles having an average primary particle size of 1 to 120 nm. In the present invention, the term "oxide ceramic formed body" refers to a formed body of oxide ceramic in which necking (adhesion) between particles of the oxide ceramic does not occur.

[0017] Oxide ceramic particles The oxide ceramic particles used in the present invention are not particularly limited, and examples thereof include those containing zirconia, alumina, titania, silica, niobium oxide, tantalum oxide, yttria, etc. One type of oxide ceramic may be used alone, or two or more types may be used in combination. Among these, from the viewpoint of applicability to dental applications such as dental prostheses, those containing zirconia and / or alumina are preferred, those containing zirconia are more preferred, and those containing zirconia as the main component are even more preferred. Hereinafter, an embodiment in which the oxide ceramic particles contain zirconia as a main component will be described, while also describing the case in which the oxide ceramic is alumina as appropriate.

[0018] Zirconia particles The zirconia particles used in the present invention preferably contain zirconia as the main component. The "main component" may be 50% by mass or more. The zirconia content in the zirconia particles according to the present invention is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, particularly preferably 80% by mass or more, and most preferably 85% by mass or more. The average primary particle size of the zirconia particles is not particularly limited, but is preferably 90 nm or less, more preferably 70 nm or less, and even more preferably 30 nm or less, from the viewpoint of obtaining a zirconia sintered body with superior translucency and strength and more significantly exhibiting the effects of the present invention. The average primary particle size of the zirconia particles is preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more, from the viewpoint of obtaining a zirconia sintered body with superior translucency and strength and more significantly exhibiting the effects of the present invention. The average primary particle diameter of the zirconia particles can be determined, for example, by photographing the zirconia particles (primary particles) with a transmission electron microscope (TEM), measuring the particle diameter (maximum diameter) of any 100 particles on the obtained image, and calculating the average value (number-based, arithmetic mean diameter) of these particles. A commercially available transmission electron microscope (TEM) can be used.

[0019] Another embodiment is a method for producing an oxide ceramic molded body, in which a powder containing oxide ceramic particles having an average primary particle size of 1 to 120 nm is press-molded under reduced pressure, and the powder containing oxide ceramic particles is a powder containing alumina particles. In the method for producing an oxide ceramic molded body of the present invention, when a powder containing alumina is used, it is preferable that the powder contains alumina as a main component. The "main component" has the same meaning as in the zirconia particles. The alumina content in the alumina particles of the present invention is 50% by mass or more. The alumina content in the alumina particles of the present invention is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, particularly preferably 80% by mass or more, and most preferably 85% by mass or more. The average primary particle size of the alumina particles is not particularly limited, but is preferably 115 nm or less, more preferably 110 nm or less, and even more preferably 100 nm or less, in order to obtain an alumina sintered body with superior translucency and strength and to more significantly exhibit the effects of the present invention. The average primary particle size of the alumina particles is preferably 1 nm or more, more preferably 10 nm or more, and even more preferably 40 nm or more, in order to obtain an alumina sintered body with superior translucency and strength and to more significantly exhibit the effects of the present invention.

[0020] The zirconia particles of the present invention preferably contain a stabilizer (hereinafter simply referred to as "stabilizer") capable of suppressing the phase transition of zirconia. Examples of stabilizers include yttrium oxide (YO) (hereinafter referred to as "yttria"), calcium oxide (CaO), magnesium oxide (MgO), cerium oxide (CeO) (hereinafter referred to as "ceria"), scandium oxide (ScO), niobium oxide (NbO), lanthanum oxide (LaO), erbium oxide (ErO), and praseodymium oxide (PrO). 11Examples of oxides include yttria, ... In one embodiment, a method for producing an oxide ceramic molded body is provided in which the powder containing oxide ceramic particles is a powder containing zirconia particles, and the stabilizer is yttria, because this allows for the production of a zirconia sintered body with excellent translucency and strength.

[0021] The stabilizer content of the zirconia particles used can be the same as the stabilizer content of the target zirconia calcined body or zirconia sintered body. Because a zirconia sintered body with superior translucency and strength can be obtained, the stabilizer content of the zirconia particles is preferably 2.0 mol% or more, more preferably 3.0 mol% or more, even more preferably 4.0 mol% or more, particularly preferably 4.5 mol% or more, and may even be 5.0 mol% or more, or even 5.5 mol% or more. The stabilizer content of the zirconia particles is preferably 9.0 mol% or less, more preferably 8.0 mol% or less, and even more preferably 7.0 mol% or less. The stabilizer content of the zirconia particles refers to the ratio (mol%) of the number of moles of yttria to the total number of moles of zirconia and stabilizer. The content of the stabilizer in the zirconia particles can be measured by, for example, inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis (XRF), or the like. The stabilizer content in the zirconia molded body, the zirconia calcined body, and the zirconia sintered body can be measured by the same method as the method for measuring the stabilizer content in the zirconia particles.

[0022] The method for preparing zirconia particles is not particularly limited, and examples thereof include a breakdown process in which coarse particles are pulverized into fine particles, a building-up process in which atoms or ions are synthesized through a nucleation and growth process, etc. Of these, the building-up process is preferred for obtaining high-purity fine zirconia particles.

[0023] The breakdown process can be carried out by pulverizing the material using a known pulverizer such as a ball mill or a bead mill. It is preferable to use pulverizing media of a very small size, for example, 100 μm or less. It is also preferable to classify the material after pulverization.

[0024] On the other hand, examples of build-up processes include gas-phase pyrolysis, in which an oxide is precipitated by thermal decomposition while vaporizing an oxyacid salt of a metal ion or an organometallic compound; a gas-phase reaction method, in which synthesis is carried out by a gas-phase chemical reaction between a gaseous metal compound with a high vapor pressure and a reactant gas; an evaporation concentration method, in which a raw material is heated and vaporized and then rapidly cooled in an inert gas at a predetermined pressure to condense the vapor into fine particles; a melt method, in which a molten liquid is cooled into small droplets and solidified to form a powder; a solvent evaporation method, in which a solvent is evaporated to increase the concentration in the liquid to a supersaturated state, and then precipitates; and a precipitation method, in which the solute concentration is supersaturated by reaction with a precipitant or hydrolysis, and then sparingly soluble compounds such as oxides and hydroxides are precipitated through a nucleation-growth process.

[0025] Precipitation methods are further subdivided into homogeneous precipitation, in which a precipitant is produced in a solution by a chemical reaction, eliminating localized unevenness in the precipitant concentration; coprecipitation, in which multiple metal ions coexisting in a solution are simultaneously precipitated by adding a precipitant; hydrolysis, in which an oxide or hydroxide is obtained by hydrolysis from a metal salt solution or an alcohol solution of a metal alkoxide, etc.; and solvothermal synthesis, in which an oxide or hydroxide is obtained from a high-temperature, high-pressure fluid. Solvothermal synthesis is further subdivided into hydrothermal synthesis, in which water is used as a solvent, and supercritical synthesis, in which a supercritical fluid such as water or carbon dioxide is used as a solvent.

[0026] In any of the build-up processes, it is preferable to increase the deposition rate in order to obtain finer zirconia particles, and it is also preferable to classify the obtained zirconia particles.

[0027] As the zirconium source in the building-up process, for example, nitrates, acetates, chlorides, alkoxides, etc. can be used, and specifically, zirconium oxychloride, zirconium acetate, zirconyl nitrate, etc. can be used.

[0028] In addition, in order to set the content of the stabilizer contained in the zirconia particles within the above range, the stabilizer can be blended during the production process of the zirconia particles, for example, by dissolving the stabilizer in the zirconia particles. As mentioned above, yttria is preferred as the stabilizer. As the yttrium source, for example, nitrates, acetates, chlorides, alkoxides, etc. can be used, and specifically, yttrium chloride, yttrium acetate, yttrium nitrate, etc. can be used.

[0029] If necessary, the zirconia particles may be surface-treated in advance with a known surface treatment agent such as an organic compound having an acidic group; a fatty acid amide such as saturated fatty acid amide, unsaturated fatty acid amide, saturated fatty acid bisamide, or unsaturated fatty acid bisamide; or an organometallic compound such as a silane coupling agent (organosilicon compound), an organotitanium compound, an organozirconium compound, or an organoaluminum compound.

[0030] Powder containing zirconia particles There are no particular limitations on the method for preparing the powder containing zirconia particles. For example, powdered zirconia particles may be used as they are, or the powder may be prepared by dry-blending powdered zirconia with powdered optional components (e.g., a fluorescent agent, a colorant, a translucency adjuster, etc.). However, it is preferable to obtain the powder by drying a slurry containing zirconia particles, because this allows for the production of a more uniform zirconia molded body with excellent physical properties, and ultimately a zirconia calcined body or zirconia sintered body.

[0031] (1) Slurry containing zirconia particles The method for preparing the slurry containing zirconia particles is not particularly limited, and it can be obtained, for example, by mixing zirconia particles with a dispersion medium. The slurry containing zirconia particles may be obtained through the above-mentioned breakdown process or building-up process, or may be commercially available.

[0032] The zirconia particles may contain a fluorescent agent. There are no particular limitations on the type of fluorescent agent used, and one or more types of fluorescent agents that can emit fluorescence when exposed to light of any wavelength may be used. The fluorescent agent may include one containing a metal element. Examples of the metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one or more of these metal elements. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, and Bi and Eu are more preferred, as they more significantly enhance the effects of the present invention. Examples of the fluorescent agent that can be used include oxides, hydroxides, acetates, and nitrates of the above metal elements. The fluorescent agents are Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl. 10 O 17 :Eu, etc.

[0033] The content of the fluorescent agent is not particularly limited and can be adjusted appropriately depending on the type of fluorescent agent, the application of the finally obtained zirconia sintered body, etc. From the viewpoint of enabling the finally obtained zirconia sintered body to be preferably used as a dental prosthesis, the content of the fluorescent agent is preferably 0.001 mass% or more, more preferably 0.005 mass% or more, and even more preferably 0.01 mass% or more, calculated as the oxide of the metal element contained in the fluorescent agent relative to the mass of zirconia used. The content of the fluorescent agent is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. When the content is equal to or greater than the lower limit, a zirconia sintered body having fluorescence comparable to that of human natural teeth can be obtained. When the content is equal to or less than the upper limit, a decrease in the translucency and strength of the zirconia sintered body can be suppressed.

[0034] The zirconia sintered body becomes a colored zirconia sintered body by containing a colorant. The type of colorant that can be contained in the slurry is not particularly limited, and known pigments that are generally used to color ceramics, known dental liquid colorants, etc. can be used. Examples of colorants include those containing metal elements, specifically oxides, composite oxides, salts, etc. containing metal elements such as iron, vanadium, praseodymium, erbium, chromium, nickel, manganese, etc. Commercially available colorants can also be used. As a commercially available colorant, for example, Colour Liquid Prettau (registered trademark) manufactured by Zirkonzahn (Italy) can be used. The above slurry may contain one type of colorant or may contain two or more types of colorants.

[0035] The content of the colorant is not particularly limited and can be adjusted appropriately depending on the type of colorant and the application of the final zirconia sintered body. From the viewpoint of enabling the final zirconia sintered body to be preferably used as a dental prosthesis, the content of the colorant is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, calculated as the oxide of the metal element contained in the colorant relative to the mass of zirconia used. Furthermore, the content of the colorant is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and may be 0.1% by mass or less, or even 0.05% by mass or less.

[0036] The zirconia particles may contain a light-transmitting modifier. Examples of light-transmitting modifiers include aluminum oxide, titanium oxide, silicon dioxide, zircon, lithium silicate, and lithium disilicate. The slurry may contain one type of light-transmitting modifier, or two or more types of light-transmitting modifiers.

[0037] The content of the light-transmitting adjuster is not particularly limited and can be appropriately adjusted depending on the type of light-transmitting adjuster, the application of the finally obtained zirconia sintered body, etc. From the viewpoint that the finally obtained zirconia sintered body can be preferably used as a dental prosthesis, the content of the light-transmitting adjuster is preferably 0.1 mass% or less relative to the mass of zirconia used.

[0038] (2) Powder containing zirconia particles The method for preparing the powder containing zirconia particles is preferably to dry a slurry containing zirconia particles, since this method can provide a more uniform and superior physical property zirconia molded body, and in turn a zirconia calcined body or zirconia sintered body, etc. The slurry to be dried here may contain at least one of a fluorescent agent, a colorant, and a translucency adjuster, as described above.

[0039] When the slurry to be dried contains a fluorescent agent, the method of adding the fluorescent agent is not particularly limited; a powdered fluorescent agent may be added. However, it is preferable to prepare a slurry containing zirconia particles and a fluorescent agent by mixing the slurry containing zirconia particles with a liquid fluorescent agent, since this prevents the inclusion of coarse particles and allows for the production of a zirconia sintered body with superior translucency and strength despite the presence of the fluorescent agent. Examples of the liquid fluorescent agent include a solution or dispersion of the fluorescent agent, with a fluorescent agent solution being preferred. The type of solution is not particularly limited, and examples include aqueous solutions. The aqueous solution may be a dilute nitric acid solution, a dilute hydrochloric acid solution, or the like, and can be selected appropriately depending on the type of fluorescent agent used.

[0040] Furthermore, when the slurry to be dried contains a colorant and / or a light-transmitting adjuster, the method for adding the colorant and / or the light-transmitting adjuster is not particularly limited. A powdered colorant and / or a light-transmitting adjuster may be added to a slurry containing zirconia particles, but it is preferable to mix the colorant and / or the light-transmitting adjuster in a liquid state such as a solution or dispersion with the slurry containing zirconia particles.

[0041] There are no particular limitations on the drying method used to dry the slurry containing zirconia particles, and it is possible to employ, for example, spray drying, supercritical drying, freeze drying, hot air drying, filtration drying, reduced pressure drying, etc. Among these, any of spray drying, supercritical drying, and freeze drying is preferred, any of spray drying and supercritical drying is more preferred, and spray drying is even more preferred, because it is possible to suppress aggregation of particles during drying and thereby obtain a denser zirconia sintered body, and a zirconia sintered body having superior translucency and strength can be obtained.

[0042] The slurry containing zirconia particles to be dried may be a slurry in which the dispersion medium is water, but it is preferable that the slurry be a slurry in which the dispersion medium is other than water, such as an organic solvent, because this can suppress aggregation of particles during drying and allow a denser zirconia sintered body to be obtained.

[0043] Examples of organic solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butyl alcohol, 2-methoxyethanol, 2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol, diethylene glycol monobutyl ether, and glycerin; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, diethyl ether, diisopropyl ether, 1,4-dioxane, and dimethoxyethane (including modified ethers such as propylene glycol monomethyl ether acetate (commonly known as "PGMEA") (preferably ether-modified ethers and / or ester-modified ethers, more preferably ether-modified alkylene glycols and / or ester-modified alkylene glycols)); esters such as ethyl acetate and butyl acetate; hydrocarbons such as hexane and toluene; and halogenated hydrocarbons such as chloroform and carbon tetrachloride. These organic solvents may be used alone or in combination of two or more. Among these, taking into consideration both safety to living organisms and ease of removal, the organic solvent is preferably a water-soluble organic solvent, and specifically, ethanol, 2-propanol, tert-butyl alcohol, 2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol, propylene glycol monomethyl ether acetate, acetone, and tetrahydrofuran are more preferred.

[0044] Furthermore, particularly when spray drying is employed, it is preferable that the dispersion medium of the slurry containing zirconia particles to be dried contains a liquid having a surface tension of 50 mN / m or less at 25°C, since this can suppress aggregation of particles during drying and result in a denser zirconia sintered body with superior translucency and strength. From this viewpoint, the surface tension of the liquid is preferably 40 mN / m or less, and more preferably 30 mN / m or less.

[0045] The surface tension at 25°C can be determined using values ​​described in, for example, the Handbook of Chemistry and Physics. For liquids not described therein, values ​​described in International Publication No. 2014 / 126034 can be used. For liquids not described in any of these publications, the surface tension can be determined using known measurement methods, such as the hanging ring method or the Wilhelmy method. The surface tension at 25°C is preferably measured using an automatic surface tensiometer "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. or a "SIGMA702" manufactured by Biolin Scientific (Sweden).

[0046] As the liquid, an organic solvent having the above surface tension can be used. As the organic solvent, any of the above-mentioned organic solvents having the above-mentioned surface tension can be used. However, at least one selected from the group consisting of methanol, ethanol, 2-methoxyethanol, 1,4-dioxane, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol is preferred, and at least one selected from the group consisting of methanol, ethanol, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol is more preferred, because it can suppress aggregation of particles during drying and thereby produce a denser zirconia sintered body.

[0047] The content of the liquid in the dispersion medium is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, because this can suppress aggregation of particles during drying and allow a denser zirconia sintered body to be obtained.

[0048] A slurry containing a dispersion medium other than water can be obtained by substituting the dispersion medium for a slurry containing water. There are no particular limitations on the method for substituting the dispersion medium. For example, a method can be employed in which a dispersion medium other than water (such as an organic solvent) is added to a slurry containing water, followed by distilling off the water. When distilling off the water, part or all of the dispersion medium other than water may be distilled off. The addition of the dispersion medium other than water and the distillation off of the water may be repeated multiple times. Alternatively, a method can be employed in which a dispersion medium other than water is added to a slurry containing water, followed by precipitating the dispersoid. Furthermore, the dispersion medium of a slurry containing water may be substituted with a specific organic solvent, and then further substituted with another organic solvent.

[0049] In addition, when the slurry containing zirconia particles to be dried contains a fluorescent agent, the fluorescent agent may be added after the dispersion medium is replaced, but it is preferable to add the fluorescent agent before the dispersion medium is replaced, because a more uniform zirconia sintered body with excellent physical properties can be obtained. Similarly, when the slurry containing zirconia particles to be dried contains a colorant and / or a translucency adjuster, the colorant and / or the translucency adjuster may be added after the dispersion medium is replaced, but it is preferable to add the colorant and / or the translucency adjuster before the dispersion medium is replaced, because a more uniform zirconia sintered body with excellent physical properties can be obtained.

[0050] The slurry containing zirconia particles to be dried may be one that has been subjected to a dispersion treatment using heat or pressure, such as reflux treatment or hydrothermal treatment. The slurry containing zirconia particles to be dried may also be one that has been subjected to a mechanical dispersion treatment using a roll mill, colloid mill, high-pressure jet disperser, ultrasonic disperser, vibration mill, planetary mill, bead mill, etc. Only one of the above treatments may be used, or two or more of them may be used.

[0051] The slurry containing zirconia particles to be dried may further contain one or more of other components such as a binder, a plasticizer, a dispersant, an emulsifier, an antifoaming agent, a pH adjuster, a lubricant, etc. The inclusion of such other components (particularly a binder, a dispersant, an antifoaming agent, etc.) may prevent particles from aggregating during drying, thereby making it possible to obtain a denser zirconia sintered body.

[0052] Examples of binders include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.

[0053] Examples of the plasticizer include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0054] Examples of dispersants include ammonium polycarboxylate (e.g., triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic acid ester copolymer, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (e.g., polyoxyethylene alkyl ether phosphate esters such as polyoxyethylene lauryl ether phosphate esters), nonionic surfactants, oleic glycerides, amine surfactants, and oligosaccharide alcohols.

[0055] Examples of emulsifiers include alkyl ethers, phenyl ethers, sorbitan derivatives, and ammonium salts.

[0056] Examples of the antifoaming agent include alcohol, polyether, polyethylene glycol, silicone, and wax.

[0057] Examples of pH adjusters include ammonia, ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide), alkali metal salts, and alkaline earth metal salts.

[0058] Examples of the lubricant include polyoxyethylene alkylate ether and wax.

[0059] The water content of the slurry containing zirconia particles to be dried is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, because this can prevent aggregation of particles during drying and allow a denser zirconia sintered body to be obtained. The water content can be measured using a Karl Fischer moisture meter.

[0060] The drying conditions in each of the above drying methods are not particularly limited, and known drying conditions can be appropriately adopted. When an organic solvent is used as the dispersion medium, in order to reduce the risk of explosion during drying, it is preferable to carry out drying in the presence of a non-flammable gas, and more preferably in the presence of nitrogen.

[0061] The supercritical fluid used in supercritical drying is not particularly limited, and for example, water, carbon dioxide, etc. can be used. However, it is preferable that the supercritical fluid is carbon dioxide, since this can suppress aggregation of particles and thereby produce a denser zirconia sintered body.

[0062] ·Method of manufacturing zirconia compacts In the method for producing a zirconia molded body of the present invention, a powder containing zirconia particles is press-molded under reduced pressure. There are no particular limitations on the specific press-molding method, and there are no particular limitations on the press molding machine as long as it is equipped with a device capable of reducing the pressure. Specific press-molding methods include, for example, uniaxial pressing. When using a powder containing zirconia particles (preferably zirconia particles containing yttria as a stabilizer) with an average primary particle diameter of 1 to 120 nm, press-molding under reduced pressure reduces the amount of air remaining in the pressed body, ensuring airtightness in the pressed body (zirconia molded body), improving moldability, and improving the production yield in the production of zirconia molded bodies.

[0063] The powder containing zirconia particles used for press molding may further contain at least one of the above-mentioned fluorescent agent, colorant, and translucency adjuster. The powder containing zirconia particles may also further contain one or more of the above-mentioned other components, such as binder, plasticizer, dispersant, emulsifier, antifoaming agent, pH adjuster, and lubricant. These components may be blended when preparing the powder.

[0064] Regarding the method of pressing under reduced pressure, there are no particular limitations on the press molding machine as long as it is equipped with a device capable of reducing pressure. Examples include a powder molding machine (product name "500kN Vibration Wave Molding Machine", manufactured by NPA Systems Co., Ltd.), a vacuum press molding machine (product name "250ton Vacuum Press Molding Machine", manufactured by Iwaki Kogyo Co., Ltd.), and a manual hydraulic vacuum heating press (model "IMC-11FD", manufactured by Imoto Machinery Co., Ltd.). Powder containing zirconia particles is filled into a pressing mold (die) of the desired size, and a pressure reducing device is operated to reduce the pressure on the powder containing zirconia particles.

[0065] The degree of vacuum may be appropriately set depending on the size of the target compact and the type and particle size of the powder containing zirconia particles, but is preferably 100 kPa or less, more preferably 95 kPa or less, and even more preferably 85 kPa or less. The degree of vacuum is preferably 0.1 kPa or more, more preferably 1 kPa or more, and even more preferably 5 kPa or more. If the degree of vacuum is higher than 100 kPa, the effect of improving moldability due to the reduced pressure cannot be obtained. If the degree of vacuum is lower than 0.1 kPa, it becomes difficult to ensure airtightness, making it difficult to stably obtain compacts.

[0066] The method for press-molding the powder containing zirconia particles under reduced pressure after placing the powder containing zirconia particles under reduced pressure as described above is not particularly limited, and any known method can be used, such as a method of applying pressure by uniaxial pressing using an upper punch and a lower punch. The temperature under reduced pressure and during press molding is not particularly limited, and heat treatment may be carried out. If heat treatment is carried out, the temperature may be about 45 to 90°C. In one embodiment, a method is mentioned in which a powder containing zirconia particles is press-molded under reduced pressure at room temperature without heating.

[0067] The load pressure in press molding (e.g., the pressure in a uniaxial press) may be appropriately set depending on the size of the target molded body and the type and particle diameter of the powder containing zirconia particles, but is typically 10 MPa or higher. When the load pressure in press molding is 10 MPa or higher, the zirconia particles are densely packed, reducing the gaps between the zirconia particles, resulting in a larger mass (content) of zirconia particles per unit mass of the zirconia molded body. A zirconia sintered body obtained from a zirconia molded body with a high content of zirconia particles has better translucency and strength. Therefore, the higher the load pressure in press molding, the better. For example, the load pressure in press molding is preferably 10 MPa or higher, more preferably 20 MPa or higher, and even more preferably 25 MPa or higher. From the viewpoint of the size of the molded body or productivity, the load pressure in the press molding is, for example, 200 MPa or less, preferably 180 MPa or less, more preferably 150 MPa or less, even more preferably 100 MPa or less, and particularly preferably 80 MPa or less. In particular, the load pressure in the press molding is preferably 10 to 200 MPa, more preferably 20 to 100 MPa, and even more preferably 25 to 80 MPa. The time for the pressing operation may be appropriately set depending on the pressing pressure, but is usually 1 to 120 minutes.

[0068] In the method for producing a zirconia molded body of the present invention, uniaxial pressing can also be carried out while simultaneously applying a pressure reduction from an unreduced state (atmospheric pressure).

[0069] When a powder containing oxide ceramic particles (preferably zirconia particles containing yttria as a stabilizer) with an average primary particle size of 1 to 120 nm is used for press molding under reduced pressure, the remaining air in the pressed body is reduced, ensuring the airtightness of the oxide ceramic molded body, improving moldability, and improving the production yield in the manufacture of oxide ceramic molded bodies. Because the present invention can solve the problems specific to powders containing oxide ceramic particles with an average primary particle size of 1 to 120 nm, the oxide ceramic molded body of the present invention is not limited to zirconia, and any of the above-mentioned oxide ceramics (e.g., alumina) can achieve the same effects as zirconia. Therefore, zirconia can be read as oxide ceramics (e.g., alumina) unless otherwise applicable.

[0070] The powder containing oxide ceramic particles may be one type alone or two or more types in combination. In one embodiment, the powder containing oxide ceramic particles is a powder containing zirconia particles and / or a powder containing alumina particles, in a method for producing an oxide ceramic molded body.

[0071] A cold isostatic pressing (CIP) step may also be included after the uniaxial pressing. The pressing pressure in the CIP step is preferably 30 MPa or more, more preferably 50 MPa or more, and even more preferably 100 MPa or more. The pressing pressure is preferably 500 MPa or less, more preferably 400 MPa or less, and even more preferably 300 MPa or less. The time for press molding in the CIP step may be appropriately set depending on the pressing pressure, but is usually 1 to 60 minutes.

[0072] In one embodiment, a humidification treatment may be performed as in Patent Document 1. Specifically, the zirconia molded body obtained by the uniaxial pressing may be used as a wet preform, and the wet preform (zirconia molded body) may be humidified to obtain a wet molded body, and the obtained wet molded body, i.e., the zirconia molded body, may be pressurized. The pressurization treatment is preferably an isostatic pressurization treatment such as CIP. The pressurization conditions may be the same as those for the CIP process.

[0073] The moisture content of the wet preform is preferably 2% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1% by mass or less, since this more significantly exhibits the effects of the present invention. The moisture content of the wet preform can be calculated as a percentage by dividing the difference between the mass of the wet preform and the mass after drying by the mass of the wet preform.

[0074] The method of humidification is not particularly limited, and can be, for example, a method of humidifying using a humidistat, a method of immersing in a water bath, a method of spraying water using a spray nozzle, etc. Among these, the method of humidifying using a humidistat is preferred because it is easy to operate and can give a uniformly wet molded body, and the method of humidifying using a thermo-hygrostat is more preferred.

[0075] When humidifying using a humidifier, the humidifying temperature is preferably 5° C. or higher, more preferably 10° C. or higher, and even more preferably 20° C. or higher, since this more significantly enhances the effects of the present invention. The humidifying temperature is also preferably 50° C. or lower, more preferably 40° C. or lower, and even more preferably 30° C. or lower.

[0076] When humidifying using a hygrometer, the relative humidity during humidification depends on the temperature and humidification time employed, but from the viewpoint of more pronounced effects of the present invention and productivity, the relative humidity at the temperature employed is preferably 60% RH or higher, more preferably 65% ​​RH or higher, even more preferably 75% RH or higher, and particularly preferably 85% RH or higher.

[0077] The humidification time when humidifying using a humidifier depends on the temperature and relative humidity employed, but is preferably 1 hour or more, more preferably 5 hours or more, and even more preferably 10 hours or more, from the viewpoint of more pronounced effects of the present invention and productivity, etc. The humidification time is preferably 7 days or less, more preferably 3 days or less.

[0078] The amount of moisture increase due to the humidification treatment depends on the particle size of the zirconia particles contained, but in order to more significantly exhibit the effects of the present invention, it is preferably more than 2 mass%, more preferably more than 3 mass%, even more preferably more than 4 mass%, and particularly preferably more than 5 mass%, based on the mass of the wet preform. Moreover, the amount of moisture increase is preferably 15 mass% or less, more preferably 13 mass% or less, and even more preferably 11 mass% or less. When the amount of moisture increase due to the humidification treatment exceeds the above-mentioned lower limit, the density can be more effectively improved during the subsequent pressure treatment. Also, when the amount of moisture increase due to the humidification treatment is equal to or less than the above-mentioned upper limit, the occurrence of cracks and the like can be more effectively suppressed during drying after the pressure treatment described below or during calcination or sintering of the obtained zirconia molded body. The amount of moisture increase due to the humidification treatment can be calculated as a percentage by subtracting the mass of the wet pre-molded body from the mass of the wet pre-molded body and dividing the result by the mass of the wet pre-molded body.

[0079] After the pressure treatment, drying may be carried out. There are no particular limitations on the drying conditions when carrying out a drying treatment, but the drying treatment temperature is preferably 50° C. or higher, more preferably 80° C. or higher, and even more preferably 100° C. or higher. The drying treatment temperature is preferably 200° C. or lower, more preferably 150° C. or lower, and even more preferably 120° C. or lower. The drying time is preferably 30 minutes or more, more preferably 1 hour or more, and even more preferably 2 hours or more, and is preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 6 hours or less. The pressure during drying may be atmospheric pressure, or may be reduced to less than 1 atmosphere, or may be dried essentially under vacuum. When drying is performed, the moisture content of the zirconia molded body obtained after drying is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. The moisture content of the zirconia molded body can be determined as a percentage by dividing the difference between the mass of the zirconia molded body and the mass after bone drying by the mass of the zirconia molded body.

[0080] By carrying out the humidification treatment and the pressure treatment and using the zirconia molded body that has undergone the humidification treatment, a zirconia sintered body that is excellent in translucency and strength can be easily produced at a high production yield.

[0081] Alternatively, a compact can be obtained by stacking and press-molding powders containing two or more different types of zirconia particles. For example, a uniaxial press die may be filled with a powder containing first zirconia particles, followed by press-molding. A powder containing second zirconia particles may then be loaded onto the pressed powder containing first zirconia particles and press-molded again to obtain a compact. The compact obtained by the above method has a structure in which a layer of powder containing first zirconia particles and a layer of powder containing second zirconia particles are laminated. The pressing pressure during press-molding may be appropriately set depending on the type and amount of powder containing zirconia particles used, and the pressing pressure may be different for each layer. Alternatively, a powder containing first zirconia particles may be filled into a mold, and then a powder containing second zirconia particles may be filled on top of the powder containing first zirconia particles, and the powder containing first zirconia particles and the powder containing second zirconia particles may be press-molded together.

[0082] There are no particular limitations on the shape of the molded body, and the mold can be changed to a desired shape depending on the application of the zirconia molded body produced in the present invention. However, taking into consideration the ease of handling when obtaining a zirconia calcined body to be used as a mill blank for producing dental materials such as dental prostheses, shapes such as a disk or a prism (e.g., a rectangular parallelepiped) are preferred. The molded body may have a single-layer structure or a multi-layer structure. By using a multi-layer structure, the finally obtained zirconia sintered body can have a multi-layer structure, and its physical properties such as translucency can be locally changed.

[0083] [Zirconia molded body] The above method can produce the desired zirconia molded body. The zirconia molded body may be calcined to form a calcined zirconia body, and then sintered to form a sintered zirconia body, or the zirconia molded body may be sintered to form a sintered zirconia body.

[0084] When the zirconia sintered body contains a fluorescent agent, it is preferable that the fluorescent agent is contained in the zirconia molded body. The content of the fluorescent agent in the zirconia molded body can be appropriately adjusted depending on the content of the fluorescent agent in the resulting zirconia sintered body. The content of the fluorescent agent in the zirconia molded body is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, calculated as the oxide of the metal element contained in the fluorescent agent relative to the mass of zirconia contained in the zirconia molded body. The content of the fluorescent agent is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less.

[0085] When the zirconia sintered body contains a colorant, it is preferable that the colorant be contained in the zirconia molded body. The content of the colorant in the zirconia molded body can be adjusted appropriately depending on the content of the colorant in the resulting zirconia sintered body. The content of the colorant in the zirconia molded body, calculated as the oxide of the metal element contained in the colorant, relative to the mass of zirconia contained in the zirconia molded body, is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more. Furthermore, the content of the colorant is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and may be 0.1% by mass or less, or even 0.05% by mass or less.

[0086] When the zirconia sintered body contains a translucency modifier, the zirconia molded body preferably contains the translucency modifier. The content of the translucency modifier in the zirconia molded body can be appropriately adjusted depending on the content of the translucency modifier in the resulting zirconia sintered body. The specific content of the translucency adjuster contained in the zirconia molded body is preferably 0.1 mass % or less relative to the mass of zirconia contained in the zirconia molded body.

[0087] The stabilizer content in the zirconia molded body may be the same as the stabilizer content in the resulting zirconia sintered body, and the stabilizer content in the zirconia molded body is preferably 2.0 mol% or more, more preferably 3.0 mol% or more, even more preferably 4.0 mol% or more, particularly preferably 4.5 mol% or more, and may even be 5.0 mol% or more, or even 5.5 mol% or more. The stabilizer content is preferably 9.0 mol% or less, more preferably 8.0 mol% or less, and even more preferably 7.0 mol% or less. The content of the stabilizer in the zirconia molded body means the ratio (mol %) of the number of moles of the stabilizer to the total number of moles of zirconia and the stabilizer.

[0088] There is no particular limitation on the density of the zirconia molded body, and it varies depending on the manufacturing method of the zirconia molded body, but since a dense zirconia sintered body can be obtained, the density is set to 3.0 g / cm 3 It is preferable that the concentration is 3.2 g / cm or more. 3 More preferably, it is 3.4 g / cm or more. 3 There is no particular upper limit to the density, but it is preferably 6.0 g / cm or more. 3 Below that, 5.8g / cm 3 It can be as follows:

[0089] The shape of the zirconia molded body is not particularly limited, and any desired shape can be used depending on the application. However, in consideration of the ease of handling when obtaining a zirconia calcined body to be used as a mill blank for producing dental materials such as dental prostheses, a disk shape, a prism shape (rectangular parallelepiped shape, etc.), etc. are preferred. Furthermore, the zirconia molded body may have a single-layer structure or a multi-layer structure, which allows the finally obtained zirconia sintered body to have a multi-layer structure, and allows the physical properties such as translucency to be locally changed.

[0090] From the viewpoint of ease of handling, the zirconia molded body preferably has a biaxial bending strength in the range of 2 to 10 MPa, more preferably in the range of 5 to 8 MPa. The biaxial bending strength of the zirconia molded body can be measured in accordance with JIS T 6526:2012.

[0091] The zirconia molded body obtained by the above-mentioned manufacturing method preferably has a crystal grain size of 180 nm or less after sintering at 1100°C for 2 hours under atmospheric pressure (after being made into a zirconia sintered body; it may also be calcined at 700°C for 2 hours under atmospheric pressure and then sintered under the above-mentioned conditions). This makes it possible to easily produce a zirconia sintered body with high translucency. Since a zirconia sintered body with excellent translucency can be obtained, the crystal grain size is more preferably 140 nm or less, even more preferably 120 nm or less, and particularly preferably 115 nm or less, and may even be 110 nm or less. There is no particular lower limit to the crystal grain size, but the crystal grain size can be, for example, 50 nm or more, or even 100 nm or more. The crystal grain size of a zirconia sintered body can be determined by taking a field emission scanning electron microscope (FE-SEM) photograph of the cross section of the zirconia sintered body, arbitrarily selecting 10 particles in the photograph, and calculating the average value of their equivalent circle diameters (diameters of perfect circles with the same area).

[0092] The zirconia molded body obtained by the above-mentioned manufacturing method preferably has a three-point bending strength of 700 MPa or more after sintering at 1100°C for 2 hours under atmospheric pressure (after being made into a zirconia sintered body; it may also be calcined at 700°C for 2 hours under atmospheric pressure and then sintered under the above-mentioned conditions). This makes it possible to easily produce a zirconia sintered body with high strength. Since a zirconia sintered body with excellent strength can be obtained, the three-point bending strength is more preferably 750 MPa or more, even more preferably 800 MPa or more, and particularly preferably 850 MPa or more, and may even be 900 MPa or more. There is no particular upper limit to the three-point bending strength, but the three-point bending strength can be, for example, 1500 MPa or less, or even 1000 MPa or less. The three-point bending strength of the zirconia sintered body can be measured in accordance with JIS R 1601:2008.

[0093] The zirconia molded body obtained by the above-mentioned manufacturing method preferably has a transmittance of 35% or more at a thickness of 0.5 mm for light with a wavelength of 700 nm after sintering at 1100°C for 2 hours under atmospheric pressure (after being made into a zirconia sintered body; it may also be pre-fired at 700°C for 2 hours under atmospheric pressure and then sintered under the above-mentioned conditions). This makes it possible to easily produce a zirconia sintered body with high translucency. Since a zirconia sintered body with excellent translucency can be obtained, the transmittance is more preferably 40% or more, even more preferably 45% or more, and may be 50% or more, or even 52% or more. There is no particular upper limit to the transmittance, but the transmittance can be, for example, 60% or less. The transmittance of light with a wavelength of 700 nm at a thickness of 0.5 mm of a zirconia sintered body can be measured using a spectrophotometer. For example, a spectrophotometer (Hitachi High-Technologies Corporation, "Hitachi Spectrophotometer U-3900H") is used to transmit and scatter light generated from a light source through a sample, and measurement can be performed using an integrating sphere. In this measurement, the transmittance may be measured first in the wavelength range of 300 to 750 nm, and then the transmittance for light with a wavelength of 700 nm may be determined. The sample used for the measurement can be a disk-shaped zirconia sintered body with a diameter of 15 mm and a thickness of 0.5 mm, both sides of which have been mirror-polished.

[0094] [Method for producing zirconia calcined body] In one embodiment, there is mentioned a method for producing a calcined oxide ceramic body, in which the oxide ceramic formed body obtained by the above method is calcined. The method for producing a zirconia calcined body will be described below, taking as an example a case where the oxide ceramic formed body is a zirconia formed body. The above-mentioned zirconia molded body can be calcined to obtain a zirconia calcined body. The oxide ceramic calcined body refers to a block of oxide ceramic particles that are not completely sintered. For example, the zirconia calcined body refers to a block of zirconia particles that are not completely sintered together.

[0095] The calcination temperature (maximum temperature) when calcining the oxide ceramic molded body is preferably 300°C or higher and lower than 1100°C. The calcination temperature can be selected appropriately depending on the type of oxide ceramic, the average primary particle size of the oxide ceramic particles, and other factors, as long as the calcination temperature does not overlap with the sintering temperature (maximum sintering temperature) and results in an incompletely sintered state of the oxide ceramic particles. For example, when calcining a zirconia molded body, the calcination temperature (maximum temperature) of the zirconia molded body is preferably 300°C or higher, more preferably 400°C or higher, and even more preferably 500°C or higher, from the viewpoint of easily obtaining the desired zirconia calcined body. Furthermore, the calcination temperature is preferably lower than 900°C, more preferably 850°C or lower, and even more preferably 800°C or lower. By setting the calcination temperature at or above the lower limit, the generation of organic residues can be effectively suppressed. Furthermore, by setting the calcination temperature at or below the upper limit, excessive sintering can be prevented, which would make cutting (milling) using a cutting machine difficult.

[0096] Another embodiment includes a method for producing an alumina calcined body, in which an alumina compact is calcined. The calcination temperature (maximum temperature) of the alumina compact is preferably 700°C or higher, more preferably 750°C or higher, and even more preferably 800°C or higher, from the viewpoint of easily obtaining the desired alumina calcined body. The calcination temperature is preferably less than 1100°C, more preferably 1050°C or lower, and even more preferably 1000°C or lower. By setting the calcination temperature at or above the lower limit, it is possible to effectively suppress the generation of organic residues. Furthermore, by setting the calcination temperature at or below the upper limit, it is possible to suppress excessive sintering, which would otherwise make cutting (milling) using a cutting machine difficult.

[0097] The temperature rise rate during calcination is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more. The temperature rise rate during calcination is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. Having a temperature rise rate equal to or greater than the lower limit improves productivity. Having a temperature rise rate equal to or less than the upper limit reduces the difference in volume between the interior and exterior of the zirconia molded body and the zirconia calcined body, and, if the zirconia molded body contains an organic substance, prevents rapid decomposition of the organic substance, thereby preventing cracking or destruction.

[0098] Although there is no particular limitation on the calcination time when calcining the zirconia molded body, the calcination time is preferably 0.5 hours or more, more preferably 1 hour or more, and even more preferably 2 hours or more, in order to enable efficient and stable production of the desired calcined zirconia body with good productivity, etc. The calcination time is also preferably 10 hours or less, more preferably 8 hours or less, and even more preferably 6 hours or less.

[0099] The calcination can be carried out using a calcination furnace. There are no particular limitations on the type of calcination furnace, and for example, electric furnaces and degreasing furnaces commonly used in industry can be used.

[0100] Before being made into a zirconia sintered body, the zirconia calcined body can be cut (milled) to have a desired shape depending on the application. In particular, according to the present invention, a zirconia sintered body having excellent quality, combining high translucency and high strength, can be easily produced with a high production yield. Therefore, the zirconia sintered body is particularly suitable as a dental material for dental prostheses and the like. To obtain a zirconia sintered body for such applications, the zirconia calcined body can be cut (milled) to have a corresponding shape. There are no particular limitations on the method of cutting (milling), and it can be carried out using, for example, a known milling device.

[0101] [Zirconia calcined body] When the zirconia sintered body contains a fluorescent agent, the fluorescent agent is preferably contained in the zirconia calcined body. The content of the fluorescent agent in the zirconia calcined body can be appropriately adjusted depending on the content of the fluorescent agent in the resulting zirconia sintered body. The content of the fluorescent agent contained in the zirconia calcined body is, relative to the mass of zirconia contained in the zirconia calcined body, preferably 0.001 mass% or more, more preferably 0.005 mass% or more, and even more preferably 0.01 mass% or more in terms of the oxide of the metal element contained in the fluorescent agent. The content of the fluorescent agent is preferably 1 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less.

[0102] When the zirconia sintered body contains a colorant, it is preferable that the colorant be contained in the zirconia calcined body. The content of the colorant in the zirconia calcined body can be appropriately adjusted depending on the content of the colorant in the resulting zirconia sintered body, etc. The content of the colorant contained in the zirconia calcined body, calculated as the oxide of the metal element contained in the colorant, relative to the mass of zirconia contained in the zirconia calcined body, is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more. The content of the colorant is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and may be 0.1% by mass or less, or even 0.05% by mass or less.

[0103] When the zirconia sintered body contains a translucency modifier, the translucency modifier is preferably contained in the zirconia calcined body. The content of the translucency modifier in the zirconia calcined body can be appropriately adjusted depending on the content of the translucency modifier in the resulting zirconia sintered body. The specific content of the translucency modifier in the zirconia calcined body is preferably 0.1 mass% or less relative to the mass of zirconia contained in the zirconia calcined body.

[0104] The yttria content of the zirconia calcined body may be the same as the yttria content of the resulting zirconia sintered body, and the yttria content of the zirconia calcined body is preferably 2.0 mol% or more, more preferably 3.0 mol% or more, even more preferably 4.0 mol% or more, particularly preferably 4.5 mol% or more, and may even be 5.0 mol% or more, or even 5.5 mol% or more. The yttria content is preferably 9.0 mol% or less, more preferably 8.0 mol% or less, and even more preferably 7.0 mol% or less. The yttria content in the zirconia calcined body means the ratio (mol %) of the number of moles of yttria to the total number of moles of zirconia and yttria.

[0105] There is no particular limitation on the density of the zirconia calcined body, and although it varies depending on the method of manufacturing the zirconia molded body used for its production, it is 3.0 to 6.0 g / m 3 It is preferable that the range is 3.2 to 5.8 g / m 3 It is more preferable that the range is within the range of The density of the zirconia calcined body can be calculated, for example, as (mass of the calcined body) / (volume of the calcined body).

[0106] The shape of the zirconia calcined body is not particularly limited and can be any desired shape depending on the application, but considering handleability when used as a mill blank for producing dental materials such as dental prostheses, a disk shape, a prism shape (rectangular parallelepiped shape, etc.), etc. are preferred. As described above, the zirconia calcined body can be cut (milled) to have a desired shape depending on the application before being made into a zirconia sintered body, and the present invention also encompasses zirconia calcined bodies having such a desired shape after cutting (milling). The zirconia calcined body may have a single-layer structure or a multi-layer structure, which allows the finally obtained zirconia sintered body to have a multi-layer structure, and allows the physical properties such as translucency to be locally changed.

[0107] The three-point bending strength of the zirconia calcined body is preferably in the range of 10 to 70 MPa, and more preferably in the range of 20 to 60 MPa, from the viewpoints of being able to maintain the shape of the workpiece when processed using a cutting machine and also being able to easily perform the cutting itself. The three-point bending strength of the calcined zirconia body can be measured using a 5 mm × 40 mm × 10 mm test piece in accordance with ISO 6872:2015, except for the test piece size. The test piece's face and C-face (the surface where the corners of the test piece are chamfered at a 45° angle) are polished longitudinally with 600-grit sandpaper. The test piece is positioned so that the widest surface faces vertically (the load direction). The test piece can be measured using a universal testing machine with a span length (support distance) of 30 mm and a crosshead speed of 0.5 mm / min.

[0108] The zirconia calcined body obtained by the above-described manufacturing method preferably has a crystal grain size of 180 nm or less after sintering at 1100°C for 2 hours under atmospheric pressure (after being made into a zirconia sintered body). This makes it possible to easily produce a zirconia sintered body with high translucency. Because a zirconia sintered body with superior translucency can be obtained, the crystal grain size is more preferably 140 nm or less, even more preferably 120 nm or less, particularly preferably 115 nm or less, and may even be 110 nm or less. There is no particular lower limit to the crystal grain size, but the crystal grain size can be, for example, 50 nm or more, or even 100 nm or more. The method for measuring the crystal grain size is as described above in connection with the zirconia molded body.

[0109] The zirconia calcined body obtained by the above-described manufacturing method preferably has a three-point bending strength of 700 MPa or more after sintering at 1100°C for 2 hours under atmospheric pressure (after being made into a zirconia sintered body). This allows for easy production of a zirconia sintered body with high strength. Because a zirconia sintered body with superior strength can be obtained, the three-point bending strength is more preferably 750 MPa or more, even more preferably 800 MPa or more, particularly preferably 850 MPa or more, and may even be 900 MPa or more. There is no particular upper limit to the three-point bending strength, but the three-point bending strength can be, for example, 1500 MPa or less, or even 1000 MPa or less. The method for measuring the three-point bending strength is as described above in connection with the zirconia molded body.

[0110] The zirconia calcined body obtained by the above-described manufacturing method preferably has a transmittance of 35% or more at a 700 nm wavelength at a thickness of 0.5 mm after sintering at 1100°C under atmospheric pressure for 2 hours (after being made into a zirconia sintered body). This makes it possible to easily produce a zirconia sintered body with high translucency. Because a zirconia sintered body with excellent translucency can be obtained, the transmittance is more preferably 40% or more, even more preferably 45% or more, and may be 46% or more, 48% or more, 50% or more, or even 52% or more. There is no particular upper limit to the transmittance, but the transmittance can be, for example, 60% or less. The method for measuring the transmittance is as described above in the description of the zirconia molded body.

[0111] The calcined body and the method for producing the same of the present invention are not limited to zirconia calcined bodies as long as they are calcined bodies of the above-mentioned oxide ceramics, and the same applies to alumina, etc. Therefore, unless particularly inapplicable, the zirconia calcined body can be interpreted as an oxide ceramics calcined body (e.g., alumina calcined body, etc.). In the production of oxide ceramic molded bodies, by suppressing the occurrence of defects such as cracks or chips and improving the production yield, sintered bodies of oxide ceramics can also be produced easily and with a high production yield.

[0112] The oxide ceramics used for the oxide ceramic molded body may be one type alone or two or more types in combination. In one embodiment, the method for producing a calcined oxide ceramic body includes a zirconia molded body or an alumina molded body.

[0113] When the powder containing alumina particles contains a stabilizer, the stabilizer may be sodium oxide, potassium oxide, magnesium oxide, calcium oxide, or ceria. Known stabilizers can be used depending on the type of oxide ceramic. When the powder containing oxide ceramic particles contains both a powder containing zirconia particles and a powder containing alumina particles, the blending ratio (mass ratio) of the two can be selected according to the purpose and is not particularly limited.

[0114] [Method for producing zirconia sintered body] In one embodiment, a method for producing an oxide ceramic sintered body includes sintering an oxide ceramic molded body obtained by the above method, or an oxide ceramic calcined body obtained by the above method. The method for producing a zirconia sintered body will be described below, taking the case where the oxide ceramic is zirconia as an example. The zirconia sintered body can be obtained by sintering the above-mentioned zirconia molded body or zirconia calcined body, preferably under atmospheric pressure. The oxide ceramic sintered body refers to a state in which oxide ceramic particles are completely sintered together. For example, the zirconia sintered body refers to a state in which zirconia particles are completely sintered together.

[0115] The sintering temperature (maximum sintering temperature) when sintering the oxide ceramic formed body or the oxide ceramic calcined body is preferably 900°C or higher and 1500°C or lower. The sintering temperature can be appropriately selected depending on the type of oxide ceramic, the average primary particle size of the oxide ceramic particles, etc., as long as the oxide ceramic particles are completely sintered together and do not overlap with the calcination temperature. For example, when sintering a zirconia molded body or a zirconia calcined body, the sintering temperature (maximum sintering temperature) is preferably 900°C or higher, more preferably 1000°C or higher, and even more preferably 1050°C or higher, from the viewpoint of easily obtaining the desired zirconia sintered body, whether sintering a zirconia molded body or sintering a zirconia calcined body. Furthermore, the sintering temperature is preferably 1200°C or lower, more preferably 1150°C or lower, and even more preferably 1120°C or lower. By setting the sintering temperature at or above the lower limit, sintering can be sufficiently promoted, and a dense sintered body can be easily obtained. By setting the sintering temperature at or below the upper limit, a zirconia sintered body having a crystal grain size within the above range can be easily obtained, and if a fluorescent agent is included, deactivation of the fluorescent agent can be suppressed.

[0116] Another embodiment includes a method for producing an alumina sintered body, which includes sintering the alumina compact obtained by the above method or the alumina calcined body obtained by the above method. In both cases of sintering the alumina compact and sintering the alumina calcined body, the sintering temperature (maximum sintering temperature) is preferably 1200°C or higher, more preferably 1250°C or higher, and even more preferably 1300°C or higher, from the viewpoint of easily obtaining the desired alumina sintered body. Furthermore, the sintering temperature is preferably 1500°C or lower, more preferably 1450°C or lower, and even more preferably 1400°C or lower. By setting the sintering temperature at or above the lower limit, sintering can be sufficiently carried out, and a dense sintered body can be easily obtained. By setting the sintering temperature at or below the upper limit, an alumina sintered body having a crystal grain size within the above range can be easily obtained, and if a fluorescent agent is included, deactivation of the fluorescent agent can be suppressed.

[0117] Although there are no particular limitations on the sintering time in either the case of sintering a zirconia molded body or the case of sintering a zirconia calcined body, the sintering time is preferably 5 minutes or more, more preferably 15 minutes or more, and even more preferably 30 minutes or more, in order to enable the desired zirconia sintered body to be obtained efficiently and stably with good productivity. The sintering time is also preferably 6 hours or less, more preferably 4 hours or less, and even more preferably 2 hours or less.

[0118] In both the case of sintering a zirconia molded body and the case of sintering a zirconia calcined body, sintering can be carried out using a sintering furnace. There are no particular limitations on the type of sintering furnace, and for example, electric furnaces and degreasing furnaces used in general industry can be used. In particular, when used for dental materials, in addition to conventional sintering furnaces for dental zirconia, dental porcelain furnaces with relatively low sintering temperatures can also be used.

[0119] Although the zirconia sintered body can be easily produced without hot isostatic pressing (HIP) treatment, it is possible to further improve the translucency and strength by performing hot isostatic pressing (HIP) treatment after sintering under atmospheric pressure.

[0120] [Zirconia sintered body] The zirconia sintered body may contain a fluorescent agent. When the zirconia sintered body contains a fluorescent agent, it has fluorescence. There are no particular restrictions on the content of the fluorescent agent in the zirconia sintered body, and the content can be appropriately adjusted depending on the type of fluorescent agent, the application of the zirconia sintered body, etc. From the viewpoint of favorable use as a dental prosthesis, the content of the fluorescent agent is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, calculated as the oxide of the metal element contained in the fluorescent agent relative to the mass of zirconia contained in the zirconia sintered body. Furthermore, the content of the fluorescent agent is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. When the content is above the lower limit, the fluorescence is comparable to that of natural human teeth. When the content is below the upper limit, the decrease in translucency and strength can be suppressed.

[0121] The zirconia sintered body may contain a colorant. When the zirconia sintered body contains a colorant, the zirconia sintered body becomes a colored zirconia sintered body. The content of the colorant in the zirconia sintered body is not particularly limited, and can be appropriately adjusted depending on the type of colorant, the application of the zirconia sintered body, etc. From the viewpoint of favorable use as a dental prosthesis, the content of the colorant is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, calculated as the oxide of the metal element contained in the colorant, relative to the mass of zirconia contained in the zirconia sintered body. Moreover, the content of the colorant is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and may be 0.1% by mass or less, or even 0.05% by mass or less.

[0122] In order to adjust the translucency of the zirconia sintered body, the zirconia sintered body may contain a translucency adjuster. There are no particular restrictions on the content of the translucency adjuster in the zirconia sintered body, and it can be appropriately adjusted depending on the type of translucency adjuster and the application of the zirconia sintered body. From the viewpoint of favorable use as a dental prosthesis, the content of the translucency adjuster is preferably 0.1 mass% or less relative to the mass of zirconia contained in the zirconia sintered body.

[0123] The yttria content in the zirconia sintered body is preferably 2.0 mol% or more, more preferably 3.0 mol% or more, even more preferably 4.0 mol% or more, particularly preferably 4.5 mol% or more, and may be 5.0 mol% or more, or even 5.5 mol% or more, since this results in a zirconia sintered body with superior translucency and strength. The yttria content is preferably 9.0 mol% or less, more preferably 8.0 mol% or less, and even more preferably 7.0 mol% or less. The content of yttria in the zirconia sintered body means the ratio (mol %) of the number of moles of yttria to the total number of moles of zirconia and yttria.

[0124] The crystal grain size of the zirconia sintered body obtained by the above-mentioned manufacturing method is preferably 180 nm or less, more preferably 140 nm or less, even more preferably 120 nm or less, particularly preferably 115 nm or less, and may be 110 nm or less, from the viewpoint of superior translucency. There is no particular lower limit to the crystal grain size, but the crystal grain size can be, for example, 50 nm or more, or even 100 nm or more. The method for measuring the crystal grain size is as described above in the description of the zirconia molded body.

[0125] The three-point bending strength of the zirconia sintered body obtained by the above-mentioned manufacturing method is preferably 700 MPa or more, more preferably 750 MPa or more, even more preferably 800 MPa or more, particularly preferably 850 MPa or more, and may be 900 MPa or more, from the viewpoint of superior strength. There is no particular upper limit to the three-point bending strength, but the three-point bending strength can be, for example, 1500 MPa or less, or even 1000 MPa or less. The method for measuring the three-point bending strength is as described above in the description of the zirconia molded body.

[0126] The transmittance of light having a wavelength of 700 nm at a thickness of 0.5 mm of the zirconia sintered body obtained by the above-mentioned manufacturing method is preferably 35% or more, more preferably 40% or more, even more preferably 45% or more, and may be 46% or more, 50% or more, or even 52% or more, from the viewpoint of superior light transmittance. There is no particular upper limit to the transmittance, but the transmittance can be, for example, 60% or less, or even 57% or less. The method for measuring the transmittance is as described above in the description of the zirconia molded body.

[0127] The main crystalline phase of the zirconia sintered body obtained by the above-mentioned manufacturing method may be either tetragonal or cubic, but it is preferable that the main crystalline phase is cubic. In the zirconia sintered body, it is preferable that 10% or more of the cubic phase is cubic, more preferably 50% or more of the cubic phase, and even more preferably 70% or more of the cubic phase. The proportion of the cubic phase in the zirconia sintered body can be determined by analyzing the crystalline phase. Specifically, X-ray diffraction (XRD) measurement is performed on a mirror-finished portion of the surface of the zirconia sintered body, and the proportion can be determined using the following formula. f c = I c / (I m +I t +I c ) x 100 where f c represents the percentage of cubic crystals in the zirconia sintered body (%), and I m represents the height of the peak near 2θ = 28° (peak based on the monoclinic system), and I t represents the height of the peak near 2θ = 30° (peak based on the tetragonal crystal system), and I c represents the height of the peak near 2θ = 30° (peak based on the cubic crystal system). If the peak near 2θ = 30° appears as a peak based on the mixed phase of tetragonal and cubic crystal systems and it is difficult to separate the peak based on the tetragonal crystal system from the peak based on the cubic crystal system, the ratio of the tetragonal crystal system to the cubic crystal system can be calculated by using the Rietveld method, and this can be used as the height of the peak based on the mixed phase (I t+c) to get I t and I c can be obtained.

[0128] The zirconia sintered body obtained by the above manufacturing method preferably has a ratio of monoclinic to tetragonal and cubic crystals of 5% or less, more preferably 3% or less, and even more preferably 1% or less, after immersion in 180°C hot water for 5 hours. Having this ratio within the above range makes it possible to suppress changes in volume over time and prevent breakage, for example, when used as a dental prosthesis. This ratio can be determined by mirror-finishing the surface of the zirconia sintered body, immersing it in 180°C hot water for 5 hours, and then performing X-ray diffraction (XRD) measurement on the portion, using the following formula: f m =〔I 28 / (I 28 +I 30 )×100 (In the formula, f m represents the ratio (%) of monoclinic to tetragonal and cubic crystals in the zirconia sintered body after immersion in 180°C hot water for 5 hours. In XRD measurement, I 28 represents the peak area around 2θ=28° where the main peak of the monoclinic system appears, and I 30 represents the peak area around 2θ=30° where the main peak of the tetragonal or cubic crystal system appears.)

[0129] [Uses of zirconia sintered body] Although there are no particular limitations on the uses of the zirconia sintered body, according to the present invention, a zirconia sintered body having excellent quality, combining high translucency and high strength, can be easily produced with a high production yield, and therefore the zirconia sintered body is particularly suitable as a dental material for dental prostheses and the like, and is particularly useful not only as a dental prosthesis used in the cervical region of teeth, but also as a dental prosthesis used on the occlusal surfaces of molars or the incisal edges of anterior teeth. The zirconia sintered body of the present invention is preferably used as a dental prosthesis used in the incisal edges of anterior teeth.

[0130] The sintered body and the manufacturing method thereof of the present invention are not limited to zirconia sintered bodies as long as they are sintered bodies of the above-mentioned oxide ceramics, and the same applies to alumina, etc. Therefore, unless particularly inapplicable, zirconia sintered bodies can be read as oxide ceramic sintered bodies (e.g., alumina sintered bodies, etc.). In the production of oxide ceramic molded bodies, by suppressing the occurrence of defects such as cracks or chips and improving the production yield, oxide ceramic sintered bodies can also be easily manufactured with a high production yield. [Example]

[0131] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples, etc. The methods for measuring each physical property are as follows.

[0132] (1) Average primary particle size of oxide ceramic particles The oxide ceramic particles were photographed using a transmission electron microscope (TEM), and the particle diameter (maximum diameter) of each of 100 randomly selected particles was measured on the obtained image. The average value of these was taken as the average primary particle diameter of the oxide ceramic particles.

[0133] (2) Three-point bending strength The three-point bending strength of the oxide ceramic sintered body was measured in accordance with JIS R 1601:2008.

[0134] (3) Light transmittance (wavelength 700 nm, thickness 0.5 mm) The transmittance of light with a wavelength of 700 nm through a 0.5 mm thick oxide ceramic sintered body was measured using a spectrophotometer (Hitachi High-Technologies Corporation, "Hitachi Spectrophotometer U-3900H"), with light emitted from a light source being transmitted through and scattered by the sample, and an integrating sphere. In this measurement, the transmittance was first measured in the wavelength range of 300 to 750 nm, and then the transmittance for light with a wavelength of 700 nm was determined. For the measurement, a disk-shaped oxide ceramic sintered body with a diameter of 15 mm and a thickness of 0.5 mm and mirror-polished on both sides was used as the sample.

[0135] (4) Appearance of the compact and calcined body (cracks or chips) The appearance (cracks or chips) of the oxide ceramic formed body and the oxide ceramic calcined body was evaluated visually.

[0136] [Example 1] To an aqueous zirconia slurry containing 3 mol% yttria, "MELox Nanosize 3Y" (manufactured by MEL Chemicals, average primary particle size of zirconia particles: 14 nm, zirconia concentration: 24 mass%), was added isopropanol in an amount 9 times the volume of the zirconia slurry, and the mixture was placed in a centrifuge tube and thoroughly mixed. The mixture was then centrifuged at 4000 rpm for 15 minutes. After confirming the precipitation of white matter, the supernatant was removed, and isopropanol was added again, followed by thorough mixing and centrifugation at 4000 rpm for 10 minutes. After confirming the precipitation of white matter, the supernatant was removed, and methanol was added to the mixture to make the volume the same as the zirconia slurry used. The mixture was then thoroughly mixed to obtain a methanol-substituted slurry.

[0137] This methanol-substituted slurry was dried using a spray dryer (B-290, manufactured by Nippon Buchi Co., Ltd.) under conditions of a feed rate of 5 mL / min, an inlet temperature of 150°C, and an outlet temperature of 100°C, to obtain a powder containing zirconia particles.

[0138] Using a vacuum press molding machine (trade name "250 ton vacuum press molding machine", manufactured by Iwaki Kogyo Co., Ltd.), the obtained powder was press-molded at room temperature under a reduced pressure of 80 kPa and a uniaxial pressure of 100 MPa into a 40 mm x 20 mm x 20 mm block (1 piece). A total of 100 press-molded pieces were produced. The defective rate (%) was calculated using the number of pieces that had visible cracks or chips. The results are shown in Table 1.

[0139] The defective rate during the production of molded articles is preferably 12% or less, more preferably 8% or less, and even more preferably 5% or less, from the viewpoint of productivity of molded articles.

[0140] In the production of the 100 press-molded bodies, zirconia molded bodies that showed no visible cracks or chips were calcined at 600°C under atmospheric pressure for 3 hours to obtain zirconia calcined bodies (for example, in Example 1, 98 molded bodies were calcined). The defective rate (%) of these zirconia calcined bodies was calculated using the number of zirconia molded bodies that showed visible cracks or chips. The results are shown in Table 1.

[0141] The defective rate during production of the calcined body is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less, from the viewpoint of productivity of the calcined body.

[0142] Furthermore, of the obtained calcined bodies, those that did not have any cracks or chips were sintered to obtain sintered bodies (for example, in Example 1, 96 calcined bodies were sintered). Specifically, the sintered bodies were obtained by sintering at 1100°C for 2 hours under atmospheric pressure. The obtained sintered bodies were white. The sintered bodies were visually inspected for the presence or absence of chips or cracks, but no chips or cracks were found in any of them.

[0143] The light transmittance of the obtained zirconia sintered body was measured by the method described above. Furthermore, the three-point bending strength of the obtained zirconia sintered body was measured by the method described above (test piece size: 40 mm × 4 mm × 3 mm, span length: 30 mm). The measurement results are shown in Table 1.

[0144] [Comparative Example 1] A zirconia molded body, a zirconia calcined body, and a zirconia sintered body were obtained in the same manner as in Example 1, except that the process was carried out under atmospheric pressure instead of under reduced pressure. The light transmittance of each of the obtained zirconia sintered bodies was measured by the method described above. Furthermore, the three-point bending strength of each of the obtained plate-shaped zirconia sintered bodies was measured by the method described above (test piece size: 40 mm × 4 mm × 3 mm, span length: 30 mm). The measurement results are shown in Table 1. Because the test was not performed under reduced pressure, many chips or cracks occurred in the molded body during production of the molded body and the calcined body, resulting in a poor yield, compared to Example 1. Furthermore, the light transmittance was also poor, possibly due to internal bubbles or defects.

[0145] [Example 2] A 2-(2-ethoxyethoxy)ethanol-substituted slurry was obtained in the same manner as in Example 1, except that a water-based zirconia slurry containing 5 mol% yttria, "MELox Nanosize 5Y" (manufactured by MEL Chemicals, average primary particle size of zirconia particles: 25 nm, zirconia concentration: 25 mass%), was used as the zirconia slurry, the pressure was reduced to 20 kPa, the uniaxial pressing pressure was 160 MPa, and 2-(2-ethoxyethoxy)ethanol was used instead of methanol.

[0146] A zirconia compact, a zirconia calcined body, and a zirconia sintered body containing zirconia particles were obtained in the same manner as in Example 1, except that the 2-(2-ethoxyethoxy)ethanol-substituted slurry obtained above was used. The obtained zirconia sintered body was white. The results are shown in Table 1.

[0147] [Example 3] As the zirconia slurry, an aqueous zirconia slurry containing 4.5 mol% yttria, "MELox Nanosize 4.5Y" (manufactured by MEL Chemicals, average primary particle size of zirconia particles: 14 nm, zirconia concentration: 23 mass%), was used. Using a manual hydraulic vacuum heating press (model "IMC-11FD", manufactured by Imoto Machinery Co., Ltd.), the degree of vacuum was gradually reduced to 1 kPa and press molding was carried out at a uniaxial pressing pressure of 40 MPa. A 2-(2-ethoxyethoxy)ethanol-substituted slurry was obtained in the same manner as in Example 1, except that 2-(2-ethoxyethoxy)ethanol was used instead of methanol.

[0148] A zirconia compact, a zirconia calcined body, and a zirconia sintered body containing zirconia particles were obtained in the same manner as in Example 1, except that the 2-(2-ethoxyethoxy)ethanol-substituted slurry obtained above was used. The obtained zirconia sintered body was white. The results are shown in Table 1.

[0149] [Example 4] To the 2-(2-ethoxyethoxy)ethanol-substituted slurry obtained in the same manner as in Example 3, a nickel (II) nitrate aqueous solution was added so that the content of nickel (II) oxide (NiO) relative to the mass of zirconia was 0.02 mass% to obtain a slurry containing zirconia particles and a colorant. This was dried using a spray dryer (B-290, manufactured by Nippon Buchi Co., Ltd.) under conditions of a feed rate of 5 mL / min, an inlet temperature of 150°C, and an outlet temperature of 100°C, to obtain a powder containing zirconia particles and a colorant.

[0150] A zirconia green body, a zirconia calcined body, and a zirconia sintered body were obtained in the same manner as in Example 1, except that the powder obtained above was used and the pressure reduction was carried out at 1 kPa and a uniaxial pressing pressure of 40 MPa. The obtained zirconia sintered bodies were colored red (not fluorescent). The results are shown in Table 1. The prepared zirconia calcined bodies were milled using a milling machine (Noritake Katana (registered trademark) H-18, manufactured by Kuraray Noritake Dental Co., Ltd.) to obtain zirconia calcined bodies having a single crown shape for a maxillary central incisor and a single crown shape for a mandibular first molar, respectively. These were sintered at 1100°C for 2 hours under atmospheric pressure, thereby obtaining red-colored dental prostheses having a crown shape.

[0151] [Example 5] The 2-(2-ethoxyethoxy)ethanol-substituted slurry obtained in Example 2 was supercritically dried using a supercritical drying apparatus according to the following procedure. Specifically, the 2-(2-ethoxyethoxy)ethanol-substituted slurry was placed in a pressure vessel, which was then connected to a supercritical carbon dioxide extraction apparatus. The absence of pressure leaks was confirmed. The pressure vessel and preheating tube were then immersed in a water bath heated to 60°C, the temperature was increased to 80°C, and the pressure was increased to 25 MPa. The mixture was then allowed to stand for 10 minutes for stabilization. Next, carbon dioxide and methanol as an entrainer were introduced under predetermined conditions (temperature: 80°C, pressure: 25 MPa, carbon dioxide flow rate: 10 mL / min, entrainer (methanol) flow rate: 1.5 mL / min). After 2 hours, the introduction of methanol was stopped, and the introduction of carbon dioxide alone was continued. After 2 hours of introducing carbon dioxide alone, the carbon dioxide flow was stopped, and the pressure was gradually reduced from 25 MPa over approximately 20 minutes to atmospheric pressure while maintaining the temperature at 80°C. The pressure vessel was removed from the water bath and cooled to room temperature, then opened and the treated sample was recovered to obtain a powder containing zirconia particles.

[0152] A zirconia compact, a zirconia calcined body, and a zirconia sintered body were obtained in the same manner as in Example 1, except that the powder obtained above was used and the pressure reduction was 20 kPa and the uniaxial pressing pressure was 20 MPa. The obtained zirconia sintered bodies were white. The results are shown in Table 1.

[0153] [Example 6] A bismuth hydroxide aqueous solution was added to the 2-(2-ethoxyethoxy)ethanol-substituted slurry obtained in the same manner as in Example 3 so that the content of bismuth oxide (Bi2O3) relative to the mass of zirconia was 0.02 mass% to obtain a slurry containing zirconia particles and a fluorescent agent. This was dried using a spray dryer (B-290, manufactured by Nippon Buchi Co., Ltd.) under conditions of a feed rate of 5 mL / min, an inlet temperature of 150°C, and an outlet temperature of 100°C, to obtain a powder containing zirconia particles and a fluorescent agent.

[0154] Using the powder obtained above, a zirconia compact, a calcined zirconia body, and a zirconia sintered body were obtained in the same manner as in Example 1, except that the powder was used and a manual hydraulic vacuum heating press (model "IMC-11FD" manufactured by Imoto Machinery Co., Ltd.) was used at a reduced pressure of 0.2 kPa and a uniaxial pressing pressure of 50 MPa. The obtained zirconia sintered bodies were white and had fluorescence. The results are shown in Table 1.

[0155] In addition, zirconia calcined bodies prepared in the same manner as above were cut using a milling machine (Noritake Katana H-18, manufactured by Kuraray Noritake Dental Co., Ltd.) into zirconia calcined bodies having a single crown shape for a maxillary central incisor and a single crown shape for a mandibular first molar, and these were sintered at 1100°C for 2 hours under atmospheric pressure to obtain fluorescent dental prostheses in the shape of a crown.

[0156] [Example 7] To an aqueous zirconia slurry containing 4.5 mol% yttria, "MELox Nanosize 4.5Y" (manufactured by MEL Chemicals, average primary particle size of zirconia particles: 14 nm, zirconia concentration: 23 mass%), was added isopropanol in an amount 9 times the volume of the zirconia slurry, and the mixture was placed in a centrifuge tube and thoroughly mixed. The mixture was then centrifuged at 4000 rpm for 15 minutes. After confirming the precipitation of white matter, the supernatant was removed, and isopropanol was added again, followed by thorough mixing and centrifugation at 4000 rpm for 10 minutes. After confirming the precipitation of white matter, the supernatant was removed, and methanol was added to the mixture to make the volume the same as the zirconia slurry used. The mixture was then thoroughly mixed to obtain a methanol-substituted slurry.

[0157] This methanol-substituted slurry was dried using a spray dryer (B-290, manufactured by Nippon Buchi Co., Ltd.) at a feed rate of 5 mL / min, an inlet temperature of 150°C, and an outlet temperature of 100°C to obtain a powder containing zirconia particles. The obtained powder was press-molded into a 40 mm x 20 mm x 20 mm block (single piece) using a vacuum press molding machine (trade name "250 ton vacuum press molding machine", manufactured by Iwaki Kogyo Co., Ltd.) at a uniaxial pressure of 15 MPa under a reduced pressure of 20 kPa. A total of 100 press moldings were performed, producing 100 press-molded bodies. The defective rate (%) was calculated using the number of externally cracked or chipped bodies among the 100 press-molded bodies. The results are shown in Table 1. Subsequently, a CIP pressure of 200 MPa was applied to the compacts that had not developed cracks or chips using a CIP device (model ADW800) manufactured by Kobe Steel, Ltd. The CIP-treated zirconia compacts were then calcined at 600°C for 3 hours under atmospheric pressure to obtain calcined zirconia compacts. The defective rate (%) of these calcined compacts was calculated using the number of visible cracks or chips. The results are shown in Table 1.

[0158] [Example 8] The white zirconia particles obtained in Example 3 were designated as (A), and the red-colored zirconia particles obtained in Example 4 were designated as (B). (A) and (B) were mixed in a bag at a mass ratio of 1:2 to obtain a powder designated as (C), and (A) and (B) were mixed in a bag at a mass ratio of 2:1 to obtain a powder designated as (D). Using a vacuum press molding machine (trade name "250-ton vacuum press molding machine," manufactured by Iwaki Kogyo Co., Ltd.), powder (A), powder (C), powder (D), and powder (B) were packed in the same order, each in equal mass, and press-molded into a 40 mm × 20 mm × 20 mm block (single piece) at a uniaxial pressure of 70 MPa under a reduced pressure of 10 kPa. A total of 100 press-molded bodies were produced. The defective rate (%) was calculated using the number of 100 press-molded bodies that showed visible cracks or chips. The results are shown in Table 1. Furthermore, zirconia molded bodies that showed no visible cracks or chips were calcined at 600°C for 3 hours under atmospheric pressure to obtain zirconia calcined bodies. The defective rate (%) was calculated using the number of these calcined bodies that showed visible cracks or chips. The results are shown in Table 1.

[0159] [Example 9] The white zirconia particles obtained in Example 1 were designated as (E), the white zirconia particles obtained in Example 3 as (F), and the white zirconia particles obtained in Example 2 as (G). Using a manual hydraulic vacuum heating press (model "IMC-11FD" manufactured by Imoto Machinery Co., Ltd.), the same masses of powder (E), powder (F), and powder (G) were filled in this order, and the vacuum level was gradually reduced to 10 kPa. The mixture was then uniaxially pressed at a pressure of 100 MPa to form a 40 mm × 20 mm × 20 mm block (single piece). A total of 100 press-molded bodies were produced. The defective rate (%) was calculated using the number of 100 press-molded bodies that showed visible cracks or chips. The results are shown in Table 1. Furthermore, zirconia molded bodies that showed no visible cracks or chips were calcined at 600°C for 3 hours under atmospheric pressure to obtain zirconia calcined bodies. The defective rate (%) was calculated using the number of these calcined bodies that showed visible cracks or chips. The results are shown in Table 1.

[0160] [Example 10] A zirconia molded body, a zirconia calcined body, and a zirconia sintered body were obtained in the same manner as in Example 1, except that the pressure reduction was set to 100 kPa (no fluorescence). The results are shown in Table 1.

[0161] [Example 11] A zirconia molded body, a zirconia calcined body, and a zirconia sintered body were obtained in the same manner as in Example 1, except that the pressure reduction was set to 96 kPa (no fluorescence). The results are shown in Table 1.

[0162] [Example 12] High-purity α-alumina powder "TM-DA (manufactured by Taimei Chemical Industry Co., Ltd.)" was mixed with 1000 ppm of magnesium oxide (manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.), and the mixture was mixed and ground in ethanol using a bead mill (trade name "RMB II" manufactured by Imex Co., Ltd.) and dried to obtain a raw material powder. The average primary particle diameter of the alumina particles was 100 nm. Thereafter, press molding, calcination, and sintering were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0163] Comparative Example 2 In Example 2, a zirconia molded body, a zirconia calcined body, and a zirconia sintered body were obtained in the same manner as in Example 1, except that the process was carried out under atmospheric pressure instead of under reduced pressure. Because the process was not carried out under reduced pressure, more chips or cracks occurred in the molded body during production of the molded body and the calcined body, resulting in a lower yield than in Example 2. Furthermore, the translucency was also lower, possibly due to internal bubbles or defects.

[0164] Comparative Example 3 A zirconia molded body, a zirconia calcined body, and a zirconia sintered body were obtained in the same manner as in Example 3, except that the manufacturing conditions were changed to those shown in Table 1, and the manufacturing was carried out under atmospheric pressure instead of under reduced pressure. Because the manufacturing was not carried out under reduced pressure, many chips or cracks occurred in the molded body during manufacturing of the molded body and the calcined body, resulting in a lower yield compared to Example 3. Furthermore, the translucency was also lower, possibly due to internal bubbles or defects.

[0165] Comparative Example 4 A zirconia molded body, a zirconia calcined body, and a zirconia sintered body were obtained in the same manner as in Example 7, except that the manufacturing conditions were changed to those shown in Table 1, and the manufacturing was carried out under atmospheric pressure instead of under reduced pressure. Because the manufacturing was not carried out under reduced pressure, more chips or cracks occurred in the molded body during manufacturing of the molded body and the calcined body, resulting in a lower yield than in Example 7. Furthermore, the translucency was also lower, possibly due to internal bubbles or defects.

[0166] [Table 1] [Industrial Applicability]

[0167] The method for producing an oxide ceramic formed body of the present invention can be widely used industrially, and is particularly suitable for use as a dental material such as a dental prosthesis.

Claims

1. A powder containing oxide ceramic particles having an average primary particle size of 1 to 120 nm is press-molded under reduced pressure; The press molding is performed under a reduced pressure of 0.1 kPa or more and 85 kPa or less. A method for producing an oxide ceramic formed body.

2. The method for producing an oxide ceramic formed body according to claim 1, wherein the press forming is carried out under a reduced pressure of 0.1 kPa or more and 80 kPa or less.

3. 2. The method for producing an oxide ceramic formed body according to claim 1, wherein a load pressure in the press forming is 10 MPa or more and 200 MPa or less.

4. 2. The method for producing an oxide ceramic formed body according to claim 1, wherein the powder containing oxide ceramic particles is a powder containing zirconia particles and / or a powder containing alumina particles.

5. 5. The method for producing an oxide ceramic formed body according to claim 4, wherein the powder containing the oxide ceramic particles further contains a stabilizer capable of suppressing a phase transition of zirconia.

6. the powder containing oxide ceramic particles is a powder containing zirconia particles, 6. The method for producing an oxide ceramic formed body according to claim 5, wherein the stabilizer is yttria.

7. 7. The method for producing an oxide ceramic formed body according to claim 6, wherein the content of said yttria is 2.0 mol % or more and 9.0 mol % or less with respect to the total number of moles of zirconia and yttria.

8. A method for producing a calcined oxide ceramic body, comprising calcining the compact obtained by the method for producing an oxide ceramic body according to claim 1.

9. The method for producing an oxide ceramic calcined body according to claim 8, wherein the calcination temperature is 300°C or higher and lower than 1100°C.

10. 9. The method for producing a calcined oxide ceramic body according to claim 8, wherein the oxide ceramic molded body is a zirconia molded body or an alumina molded body.

11. A method for producing an oxide ceramic sintered body, comprising sintering an oxide ceramic formed body obtained by the method for producing an oxide ceramic formed body according to any one of claims 1 to 7, or an oxide ceramic calcined body obtained by the method for producing an oxide ceramic calcined body according to any one of claims 8 to 10.

12. The method for producing an oxide ceramic sintered body according to claim 11, wherein the sintering temperature is 900°C or higher and 1500°C or lower.

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