Zirconia calcined body and method for producing same

Abstract

The present invention provides: a zirconia calcined body that can provide a zirconia sintered body having excellent mechanical strength and light-transmitting properties; and a method for producing the zirconia calcined body. The present invention relates to a zirconia calcined body containing zirconia and a stabilizer capable of suppressing the occurrence of phase transition of zirconia, wherein the zirconia includes monoclinic zirconia, and the half-value width of a main peak derived from the monoclinic system in a powder X-ray diffraction pattern obtained using CuKα line is 0.18° or more.

Description

Zirconia calcined body and method for producing the same

[0001] The present invention relates to a zirconia calcined body and a method for producing the same. More specifically, the present invention relates to a zirconia calcined body that has excellent mechanical strength and translucency, and a method for producing the same.

[0002] Zirconia sintered bodies are widely used industrially, and in particular, in recent years have been used as dental materials for dental prostheses, etc. These dental prostheses are often produced by forming a zirconia molded body having a desired shape, such as a disk or a prism, by press-molding zirconia particles or by molding using a composition containing zirconia particles, and then calcining this to form a calcined body (mill blank), which is then cut (milled) into the shape of the desired dental prosthesis and further fired.

[0003] Zirconia is a compound that undergoes phase transitions between multiple crystal systems. Therefore, partially stabilized zirconia (PSZ) and fully stabilized zirconia (FSZ), which are formed by dissolving a stabilizer such as yttria (yttrium oxide; YO) in zirconia to suppress the phase transition, are used in various fields.

[0004] In the dental field, zirconia materials have been used as frame materials due to their high strength but low translucency. In recent years, however, as the translucency of zirconia materials has improved, dental prostheses are increasingly being made solely from zirconia.

[0005] Such dental materials using zirconia materials are disclosed, for example, in Patent Document 1.

[0006] International Publication No. 2020 / 179877

[0007] However, there is room for improvement in physical properties such as translucency of the zirconia sintered body obtained using the zirconia molded body or the zirconia calcined body according to Patent Document 1. Specifically, in Patent Document 1, the total light transmittance is evaluated using a sample having a thickness of 0.5 mm, and when used in a dental prosthesis having a thickness of, for example, 1.0 mm, there is room for improvement in translucency.

[0008] An object of the present invention is to provide a zirconia calcined body in which the resulting zirconia sintered body is excellent in mechanical strength and translucency, and a method for producing the same.

[0009] As a result of intensive research into solving the above problems, the present inventors have found that a zirconia sintered body obtained by calcining a zirconia sintered body containing zirconia and a stabilizer capable of suppressing a phase transition of the zirconia, wherein the zirconia contains monoclinic zirconia, and wherein the half-width of a main peak derived from the monoclinic system in a powder X-ray diffraction pattern using CuKα rays is 0.18° or more, can be excellent in mechanical strength and translucency. Based on this finding, the present inventors have conducted further research and have completed the present invention.

[0010] The present invention encompasses the following inventions: [1] A zirconia calcined body comprising zirconia and a stabilizer capable of suppressing a phase transition of the zirconia, wherein the zirconia comprises monoclinic zirconia, and wherein the half-width of a main peak derived from the monoclinic system in a powder X-ray diffraction pattern using CuKα radiation is 0.18° or more. [2] The zirconia calcined body according to [1], wherein the stabilizer is yttria. [3] The abundance f of yttria not dissolved in zirconia is calculated by the following formula (1-1): y The zirconia calcined body according to [2], wherein (%) is less than 4%. y (%) = I y / (I m +I t +I c +I y )×100 (1-1) (where f y is the abundance of yttria not dissolved in zirconia, f y (%), and in XRD measurement, I mrepresents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2° where the peak top of the main peak of yttria not dissolved in zirconia appears.) [4] The monoclinic fraction f calculated by the following formula (1-2) m (%) is less than 55%. m (%) = I m / (I m +I t +I c +I y )×100 (1-2) (where f m represents the monoclinic crystal ratio (%), and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2° where the peak top of the main peak of yttria not dissolved in zirconia appears.) [5] The monoclinic fraction f m[4] The zirconia calcined body according to [4], wherein the zirconia calcined body has a stabilizing agent content of 2 to 10 mol % relative to the total moles of the zirconia and the stabilizing agent. [6] The zirconia calcined body according to any one of [1] to [5], wherein the stabilizing agent content is 2 to 10 mol % relative to the total moles of the zirconia and the stabilizing agent. [8] A method for producing a zirconia calcined body according to any one of [1] to [7], comprising: a step of producing a zirconia composition containing zirconia particles and stabilizer particles capable of suppressing a phase transition of zirconia; a grinding step of grinding the zirconia composition; a molding step of molding the ground zirconia composition to obtain a green body; and a calcining step of calcining the green body, wherein the zirconia particles are monoclinic zirconia particles, and the grinding step (i) uses grinding media with a diameter of less than 1 mm and a grinding time of 10 minutes or more, or (ii) uses grinding media with a diameter of 1 mm or more and a grinding time of more than 40 hours. [9] A method for producing a zirconia calcined body according to [8], wherein the calcination temperature in the calcination step is 600 to 1200°C.

[10] A method for producing a zirconia sintered body, comprising firing the zirconia calcined body according to any one of [1] to [7] under atmospheric pressure at a maximum sintering temperature of more than 1200°C and not more than 1650°C.

[0011] According to the present invention, a zirconia calcined body having excellent mechanical strength and translucency (in-line light transmittance and total light transmittance) and a method for producing the same can be provided. Furthermore, according to the present invention, the zirconia sintered body obtained has high total light transmittance and excellent translucency even when the thickness is 1.0 mm, and therefore, when a dental material (e.g., a dental prosthesis) is produced, the aesthetic appearance is excellent. Furthermore, by using the zirconia calcined body of the present invention, a zirconia sintered body having excellent mechanical strength and translucency can be obtained at a maximum sintering temperature lower than conventional temperatures (e.g., 1450°C or lower). Furthermore, by using the zirconia calcined body of the present invention, a zirconia sintered body having excellent translucency can be obtained even when sintered for a short time, i.e., a holding time of 10 minutes or less at the maximum sintering temperature. Therefore, this contributes to further productivity improvement, such as shortening treatment time at dental clinics, and is advantageous for realizing treatment using a dental prosthesis in a single visit (one-visit treatment). Furthermore, by using the zirconia calcined body of the present invention, it is possible to provide a zirconia sintered body excellent in mechanical strength and in-line light transmittance without using a HIP apparatus. Furthermore, according to the present invention, even when the shaped body is large (for example, 20 mm thick), the calcined body can be obtained without problems such as debinding cracks.

[0012] [Zirconia Calcined Body] The zirconia calcined body of the present invention comprises zirconia and a stabilizer capable of suppressing a phase transition of the zirconia, wherein the zirconia comprises monoclinic zirconia, and the half width of the main peak derived from the monoclinic system in a powder X-ray diffraction pattern using CuKα radiation (hereinafter simply referred to as the "half width of the main peak derived from the monoclinic system" or "half width") is 0.18° or more.

[0013] As used herein, the term "zirconia composition" refers to a composition containing zirconia powder and a stabilizer powder. As used herein, the term "molded body" refers to a body that has not yet reached either a semi-sintered state (calcined state) or a sintered state. That is, a molded body is distinguished from a calcined body and a sintered body in that it is a body that has been formed by molding and then not yet fired. As used herein, the term "zirconia calcined body" refers to a body that is in a semi-sintered state in which zirconia particles are necked (adhered) to each other and are not completely sintered. As used herein, the term "zirconia sintered body" refers to a body that is in a sintered state in which zirconia particles are completely sintered. In a zirconia sintered body, the zirconia particles solidify together through sintering, and as sintering progresses, the relative density increases and densification progresses, resulting in a completely sintered state in which the relative density is 95% or more. As used herein, "zirconia" refers to zirconium (IV) oxide (ZrO), and ZrO particles contain a trace amount of HfO relative to the amount of ZrO (0.5% by mass to 3% by mass). Because HfO is difficult to separate, terms such as "zirconia," "zirconia particles," and "zirconia powder" refer to materials containing both ZrO and HfO. Furthermore, particles and powders in which a stabilizer is dissolved in zirconia are also included in the terms "zirconia particles" and "zirconia powder," respectively. As used herein, "half-width" refers to the full width at half maximum (FWHM). As used herein, "atmospheric pressure" refers to standard atmospheric pressure (1 atm). Note that, in this specification, the upper and lower limits of numerical ranges (such as temperature ranges, the content of each component, the abundance of crystalline systems, values ​​calculated from components, and each physical property) can be combined as appropriate.

[0014] The reason why the half-width of the main peak derived from the monoclinic system of zirconia contained in the zirconia calcined body of the present invention is within a predetermined range, resulting in a zirconia sintered body having excellent mechanical strength and translucency (in-line light transmittance and total light transmittance) is not clear, but is presumed to be as follows: The reduced crystallinity of the zirconia calcined body makes it possible to sinter at a lower temperature than conventional materials. As a result, it is believed that the resulting sintered body has small, uniform grain sizes and is excellent in mechanical strength and translucency (in-line light transmittance and total light transmittance).

[0015] In the zirconia calcined body of the present invention, the half-width of the main peak derived from the monoclinic system is preferably 0.19° or more, more preferably 0.20° or more, even more preferably 0.21° or more, and particularly preferably 0.22° or more, from the viewpoints of easily enabling sintering at low temperatures and easily obtaining a sintered body excellent in mechanical strength, in-line light transmittance, and total light transmittance. The upper limit of the half-width of the main peak derived from the monoclinic system is not particularly limited as long as the effects of the present invention are exhibited, but may be, for example, 0.5° or less, 0.45° or less, or 0.4° or less.

[0016] The zirconia calcined body contains a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizer").

[0017] The stabilizer content in the zirconia calcined body is preferably 2.0 mol% or more, more preferably 3.0 mol% or more, even more preferably 3.5 mol% or more, and particularly preferably 4.0 mol% or more, based on the total moles of zirconia and stabilizer. A content of 2.0 mol% or more is preferable because the crystalline system contained in the sintered body contains more cubic crystals, improving translucency (linear light transmittance and total light transmittance). Furthermore, the stabilizer content is preferably 10 mol% or less, more preferably 9.0 mol% or less, even more preferably 8.5 mol% or less, and particularly preferably 8 mol% or less. A content of 10 mol% or less is preferable because it prevents a decrease in mechanical strength.

[0018] Examples of stabilizers capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizers") include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (YO), cerium oxide (CeO), scandium oxide (ScO), niobium oxide (NbO), lanthanum oxide (LaO), erbium oxide (ErO), praseodymium oxide (PrO, PrO) and the like. 11 Examples of the stabilizer include oxides such as yttria (Y2O3), samarium oxide (Sm2O3), europium oxide (Eu2O3), thulium oxide (Tm2O3), gallium oxide (Ga2O3), indium oxide (In2O3), and ytterbium oxide (Yb2O3), with yttria (Y2O3) being preferred. The stabilizers may be used alone or in combination of two or more. In the zirconia calcined body of the present invention, the stabilizer may be yttria (Y2O3) alone, or may further contain yttria and a stabilizer other than yttria that can suppress the phase transition of zirconia.

[0019] Furthermore, the zirconia calcined body of the present invention has a half-value width of the main peak derived from the monoclinic system of zirconia within a predetermined range, and the resulting sintered body is superior in mechanical strength and translucency (straight light transmittance and total light transmittance). Therefore, the abundance f of yttria that is not dissolved in zirconia (hereinafter, also simply referred to as "undissolved yttria"), calculated by the following formula (1-1), is y (%) is preferably less than 4%. y (%) is not particularly limited as long as the effects of the present invention are exhibited, but may be less than 10%, less than 7%, or less than 5%. y (%) is 4% or more and less than 7%. y (%) = I y / (I m +I t +I c +I y )×100 (1-1) (where f y is the abundance of yttria not dissolved in zirconia, f y(%), and in XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ = 29.2°, where the peak top of the main peak of yttria not dissolved in zirconia appears.)

[0020] Undissolved yttria abundance f y The content of undissolved yttria f (%) is more preferably less than 3.5%, even more preferably 2% or less, and particularly preferably 1% or less, from the viewpoint that the zirconia sintered body obtained by the combined action of the half width within a predetermined range and the resulting zirconia sintered body has better mechanical strength and translucency (linear light transmittance and total light transmittance). y The undissolved yttria content f (%) may be 0%. y (%) can be adjusted by a grinding process or the like, as described below.

[0021] In addition, the zirconia calcined body of the present invention has a half-value width of the main peak derived from the monoclinic system of zirconia within a predetermined range, and the resulting sintered body has excellent mechanical strength and translucency (linear light transmittance and total light transmittance). Therefore, the monoclinic fraction f calculated by the formula (1-2) is preferably 0.01 to 0.1. m (%) is preferably less than 55%. m (%) = I m / (I m +I t +I c +I y )×100 (1-2) (where f m represents the monoclinic crystal ratio (%), and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I trepresents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ = 29.2°, where the peak top of the main peak of yttria not dissolved in zirconia appears.)

[0022] Monoclinic ratio f m The monoclinic fraction f (%) is more preferably less than 50%, further preferably 48% or less, and particularly preferably 45% or less, from the viewpoint that the half-width of the zirconia calcined body falls within a predetermined range and the zirconia sintered body obtained thereby is excellent in mechanical strength and translucency (linear light transmittance and total light transmittance). m (%) is preferably 5% or more, more preferably 10% or more, even more preferably 15% or more, and particularly preferably 20% or more.

[0023] The zirconia calcined body of the present invention preferably contains primary particles having an average primary particle diameter of 60 nm or more and less than 250 nm. The average primary particle diameter is more preferably 61 nm or more, even more preferably 62 nm or more, and particularly preferably 63 nm or more, from the viewpoints of suppressing a decrease in translucency while achieving excellent mechanical strength and translucency, particularly excellent in-line light transmittance. Furthermore, the average primary particle diameter is more preferably 220 nm or less, even more preferably 200 nm or less, and particularly preferably 180 nm or less. In the zirconia calcined body of the present invention, the average primary particle diameter can be appropriately selected as long as it falls within the above-described preferred range. In a preferred embodiment, the zirconia calcined body contains primary particles having an average primary particle diameter of 60 nm or more and less than 80 nm, from the viewpoint of easily obtaining a zirconia sintered body having excellent mechanical strength and translucency even when a lower maximum sintering temperature (e.g., 1450°C or less) is used. In another preferred embodiment, the zirconia calcined body contains primary particles having an average primary particle diameter of 80 nm or more and less than 200 nm. The method for evaluating the average primary particle size is as described in the Examples below.

[0024] The zirconia calcined body of the present invention may contain additives other than zirconia and stabilizers, such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (AlO), titanium oxide (TiO), and silica (SiO), as long as the effects of the present invention are achieved.

[0025] Examples of the pigment include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically, NiO, CrO, etc.) (however, YO and CeO are excluded). An oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb is preferred, and an oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb is more preferred. The zirconia calcined body of the present invention may also be free of erbium oxide (Er2O3). Examples of the composite pigment include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4.ZrSiO4, and (Co,Zn)Al2O4. Examples of the fluorescent agent include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl2O4. 10 O 17 : Eu, etc.

[0026] The zirconia calcined body of the present invention may contain a fluorescent agent. By including a fluorescent agent in the zirconia calcined body, the zirconia sintered body has fluorescence. The type of fluorescent agent is not particularly limited, and one or more fluorescent agents capable of emitting fluorescence with light of any wavelength can be used. Examples of fluorescent agents include those containing metal elements. Examples of such metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one of these metal elements alone, or two or more of them. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred. Examples of fluorescent agents 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.

[0027] The content of the fluorescent agent in the zirconia calcined body is not particularly limited and can be adjusted as appropriate depending on the type of fluorescent agent or the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the fluorescent agent content 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 100 mass% of zirconia contained in the zirconia calcined body. Furthermore, the fluorescent agent content, calculated as the oxide of the metal element contained in the fluorescent agent, is not particularly limited as long as suitable fluorescence is exhibited, but may be 1 mass% or less, 0.5 mass% or less, or even 0.1 mass% or less. When the content is equal to or greater than the lower limit, the fluorescence is comparable to that of natural human teeth. When the content is equal to or less than the upper limit, the decrease in mechanical strength and translucency can be suppressed.

[0028] The flexural strength of the zirconia calcined body of the present invention is preferably 15 MPa or more to ensure mechanical strength that allows mechanical processing in the calcined body state, and is preferably 70 MPa or less, more preferably 60 MPa or less, to facilitate mechanical processing in the calcined body state.

[0029] The bending strength can be measured in accordance with ISO 6872:2015 (Dentistry - Ceramic materials), but the only change is the size of the test specimen, which is measured using a test specimen measuring 5 mm x 10 mm x 50 mm. The test specimen's face and C-face (the surface where the corners of the test specimen are chamfered at a 45° angle) are finished in the longitudinal direction with 600-grit sandpaper. The test specimen is positioned so that the widest surface faces vertically (load direction). In the three-point bending test, the support distance (span) is 30 mm and the crosshead speed is 0.5 mm / min.

[0030] The density of the zirconia calcined body of the present invention is 2.7 g / cm 3More preferably, 3.0 g / cm 3 More preferably, it is 3.2 g / cm or more. 3 It is more preferable that the density of the zirconia calcined body is 4.0 g / cm or more. 3 Preferably, 3.8 g / cm or less 3 More preferably, 3.6 g / cm 3 The following is more preferable. When the density is within the above range, molding can be easily performed. The density of the zirconia calcined body can be calculated by (mass of the zirconia calcined body) / (volume of the zirconia calcined body). The density of the zirconia calcined body can be measured, for example, by cutting out 10 mm square test specimens (n=3) from arbitrary positions of the zirconia calcined body while changing the cutting position, measuring the mass and volume of the obtained test specimens, calculating the arithmetic mean value of the measured values, and using the arithmetic mean value to calculate the density according to the above formula.

[0031] [Method for Producing Zirconia Calcined Body] A method for producing a zirconia calcined body includes the steps of producing a zirconia composition containing zirconia particles and stabilizer particles capable of suppressing the phase transition of zirconia, a grinding step of grinding the zirconia composition, a molding step of molding the ground zirconia composition to obtain a molded body, and a calcining step of calcining the molded body, wherein the zirconia particles are monoclinic zirconia particles, and the grinding step includes a predetermined grinding process described below. Next, a method for producing a zirconia calcined body will be described using an example in which the stabilizer is yttria. The zirconia calcined body of the present invention can be produced by grinding a zirconia composition, molding the ground zirconia composition into a molded body, firing (calcining) the molded body to an extent that the zirconia particles do not sinter together, and applying excess energy to the grinding process under predetermined conditions compared to conventional techniques.

[0032] The zirconia composition before the pulverization treatment can be produced by mixing raw material powders, zirconia powder and yttria powder. The mixing method is not particularly limited, and known methods and devices can be used.

[0033] As a method for preparing the zirconia particles constituting the zirconia powder and the yttria particles constituting the yttria powder, for example, a breakdown process in which coarse particles are pulverized or crushed to produce fine particles, or a building-up process in which particles are synthesized from atoms or ions through a nucleation and growth process, can be employed. However, considering that a predetermined pulverization process is required to obtain a desired half-width in the zirconia calcined body obtained when produced by the building-up process, the breakdown process is preferred from the viewpoint of ease of production.

[0034] The method for producing a zirconia composition will be described below using a breakdown process as an example.

[0035] The zirconia constituting the zirconia powder includes monoclinic zirconia. The zirconia constituting the zirconia powder may further include tetragonal zirconia and / or cubic zirconia, so long as it contains monoclinic zirconia. As long as the zirconia powder contains monoclinic zirconia, one type of these crystal systems may be used alone, or two or more types may be used in combination.

[0036] As the zirconia powder, commercially available zirconia particles may be used, or the commercially available powder may be used after being pulverized in a known pulverizing / mixing device (such as a ball mill).As the yttria powder, commercially available yttria particles may be used, or the commercially available powder may be used after being pulverized in a known pulverizing / mixing device (such as a ball mill).

[0037] Commercially available zirconia powders include, for example, zirconia powders (trade names "Zpex (registered trademark)" (Y2O3 content: 3 mol%), "Zpex (registered trademark) 4" (Y2O3 content: 4 mol%), and "Zpex (registered trademark) Smile (registered trademark)" (YO content: 5.5 mol%), "TZ-3Y" (YO content: 3 mol%), "TZ-3YS" (YO content: 3 mol%), "TZ-4YS" (YO content: 4 mol%), "TZ-6Y" (YO content: 6 mol%), "TZ-6YS" (YO content: 6 mol%), "TZ-8YS" (YO content: 8 mol%), "TZ-10YS" (YO content: 10 mol%), "TZ-3Y-E" (YO content: 3 mol%), "TZ- Examples of such zirconia include "TZ-3YS-E" (YO content: 3 mol%), "TZ-3YB-E" (YO content: 3 mol%), "TZ-3YSB-E" (YO content: 3 mol%), "TZ-3YB" (YO content: 3 mol%), "TZ-3YSB" (YO content: 3 mol%), "TZ-3Y20AB" (YO content: 3 mol%), "TZ-8YSB" (YO content: 8 mol%), and "TZ-0" (YO content: 0 mol%; monoclinic zirconia); all manufactured by Tosoh Corporation.

[0038] Next, a zirconia composition containing zirconia particles containing monoclinic zirconia and stabilizer particles is subjected to a pulverization treatment. By applying an excess amount of energy compared to conventional techniques in the pulverization treatment under specified conditions, a zirconia calcined body can be obtained in which the half-width of the main peak derived from the monoclinic zirconia is adjusted to a desired range. Conventionally, because zirconia particles are a very hard substance, it has been difficult to reduce the size of the zirconia particles excessively, even if the amount of energy used in the pulverization treatment is increased. Therefore, there has been no technical significance in excessively pulverizing the zirconia particles. However, in the present invention, when a zirconia composition containing monoclinic zirconia and yttria is subjected to a pulverization treatment and an excess amount of energy is applied in the pulverization treatment compared to conventional techniques, it is possible to adjust the half-width of the main peak derived from monoclinic zirconia in a zirconia calcined body obtained using the zirconia composition after the pulverization treatment to within a desired range, and it is presumed that, when a sintered body is produced, it will have excellent mechanical strength and will also be excellent in both in-line light transmittance and total light transmittance, and will be able to exhibit excellent translucency.

[0039] By adjusting the half-width of the main peak derived from monoclinic zirconia in the zirconia calcined body to a desired range, the mechanical strength of the resulting sintered body can be improved. In addition, the sintered body can be excellent in both in-line light transmittance and total light transmittance, and the zirconia composition can be provided with an excess of energy to achieve excellent translucency. Therefore, the following specific operations in the milling process are preferred: (i) using milling media with a diameter of less than 1 mm for a milling time of 10 minutes or longer, or (ii) using milling media with a diameter of 1 mm or greater for a milling time of more than 40 hours. By these methods, the progress of disintegration and milling reduces the crystallinity and broadens the half-width, thereby enabling the half-width of the main peak derived from monoclinic zirconia in the resulting zirconia calcined body to be adjusted to a desired range. Furthermore, dissolution and amorphization of yttria progress during these milling processes, allowing the abundance of undissolved yttria to be adjusted to the amount calculated by Equation (1-1). The abundance of undissolved yttria can be controlled by adjusting the milling time.

[0040] When using grinding media with a diameter of less than 1 mm, the diameter of the grinding media is preferably 0.1 to 0.5 mm, because using grinding media with a fine diameter makes it easy to widen the half-width and adjust the half-width of the main peak derived from monoclinic zirconia in the obtained zirconia calcined body to a desired range. Commercially available products may be used as grinding media with a diameter of less than 1 mm. Examples of grinding devices that use grinding media with a diameter of less than 1 mm include bead mills.

[0041] When grinding media with a diameter of less than 1 mm are used, the grinding time is not particularly limited as long as it is easy to widen the half-width and adjust the half-width of the main peak derived from monoclinic zirconia in the resulting zirconia calcined body to the desired range. However, from the viewpoint of easy adjustment of the half-width of the main peak derived from monoclinic zirconia in the resulting zirconia calcined body to the desired range, it is preferably 10 minutes or more, more preferably 15 minutes or more, even more preferably 20 minutes or more, and particularly preferably 30 minutes or more. Furthermore, from the viewpoint of easy adjustment of the half-width of the main peak derived from monoclinic zirconia in the resulting zirconia calcined body to the desired range, the grinding time is preferably 20 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and particularly preferably 2 hours or less. Note that when a grinding device that grinds while circulating a slurry (e.g., a circulating bead mill) is used as the grinding device, the grinding time refers to the residence time of the slurry in the vessel (grinding chamber).

[0042] When using grinding media with a diameter of 1 mm or more, the grinding media diameter (diameter) is preferably 1.5 mm or more, and more preferably 2.0 mm or more, because this makes it easier to increase the amount of energy required for the grinding process by increasing the grinding time. Commercially available grinding media with a diameter of 1 mm or more may be used. Examples of grinding devices that use grinding media with a diameter of 1 mm or more include ball mills.

[0043] When using grinding media with a diameter of 1 mm or more, the grinding time (grinding treatment time) is not particularly limited as long as the half-width of the main peak derived from monoclinic zirconia in the resulting zirconia calcined body can be adjusted to the desired range, but is preferably more than 40 hours, more preferably 55 hours or more, and from the viewpoint of particularly facilitating adjustment of the half-width to the desired range, even more preferably 80 hours or more, and particularly preferably 100 hours or more. Furthermore, the grinding treatment time is preferably 1,000 hours or less, more preferably 800 hours or less, even more preferably 500 hours or less, and particularly preferably 300 hours or less.

[0044] In the present invention, by supplying to the zirconia composition an increased amount of milling energy adjusted by the combination of the milling time and the milling media diameter, it is possible to obtain a zirconia composition containing zirconia particles in which the half width of the main peak derived from monoclinic zirconia in the resulting zirconia calcined body is adjusted to fall within a desired range.

[0045] By producing a zirconia calcined body using the zirconia composition obtained as described above, it is presumed that the zirconia calcined body of the present invention will have excellent mechanical strength, and the sintered body will also have excellent in-line light transmittance and total light transmittance, and will therefore exhibit excellent translucency.

[0046] The zirconia composition before and after the pulverization treatment may be in the form of granules, a slurry, etc. When the zirconia composition is a slurry, the slurry can be produced by mixing the mixed powder obtained by the pulverization treatment with a solvent (preferably water).

[0047] The average particle size of the zirconia composition after the pulverization treatment is preferably 0.2 μm or less in order to provide a sintered body with excellent mechanical strength and translucency, and is preferably 20 nm or more in order to provide excellent moldability.

[0048] The average particle size of the zirconia particles and yttria particles in the zirconia composition after the pulverization treatment can be measured by a dynamic light scattering particle size distribution measurement method. For example, using a dynamic light scattering particle size distribution measurement device (product name "SZ-100V2") manufactured by Horiba, Ltd., a slurry diluted to about 0.1 mass % with water is irradiated with ultrasonic waves for 30 minutes, and then the average particle size can be measured on a volume basis while applying ultrasonic waves.

[0049] The zirconia composition may also contain additives such as a binder, a dispersant, an emulsifier, an antifoaming agent, a pH adjuster, a lubricant, a translucency adjuster, etc. The additives may be used alone or in combination of two or more.

[0050] Examples of binders include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.

[0051] In order to improve translucency, the content of the binder in the zirconia composition of the present invention is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less, relative to 100% by mass of zirconia.

[0052] Examples of the plasticizer include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0053] 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, olein glyceride, amine salt surfactants, oligosaccharide alcohols, and stearic acid.

[0054] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitan derivatives.

[0055] Examples of the antifoaming agent include alcohol, polyether, polyethylene glycol, silicone, and wax.

[0056] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide).

[0057] Examples of the lubricant include polyoxyethylene alkyl ether and wax.

[0058] Examples of the light transmittance adjusting agent include aluminum oxide (Al2O3), titanium oxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0059] The BET specific surface area of ​​the particles constituting the zirconia composition is 7.0 m when measured in accordance with JIS Z 8830:2013. 2 / g or more, and 7.5m 2 / g or more, and more preferably 8.0m 2 / g or more is more preferable. 2 When the BET specific surface area is 50 m / g or more, the sintered body is easily prevented from becoming cloudy when sintered. 2 / g or less, and 2 / g or less is more preferable, and 40m 2 / g or less is more preferable. 2 / g or less, the BET specific surface area is less susceptible to temperature variations in the firing furnace. The BET specific surface area can be measured using a commercially available product such as a fully automatic specific surface area measuring device (trade name "Macsorb (registered trademark) HM model-1200", BET flow method (single-point method / multi-point method), manufactured by Mountec Co., Ltd.). For example, it can be measured by the BET flow method (single-point method) using the fully automatic specific surface area measuring device. Furthermore, even when the firing time for sintering is shortened, the light transmittance of the sintered body is less likely to decrease. The "BET specific surface area" referred to here is a specific surface area measured without distinguishing between primary particles and secondary particles.

[0060] Next, the pulverized zirconia composition is subjected to a molding step to produce a molded body, which is obtained by applying an external force to the zirconia composition using a known method.

[0061] The molding method is not particularly limited, and the following methods can be used, for example: (a) a step of slip-casting a slurry containing the pulverized zirconia composition; (b) a step of gel-casting a slurry containing the pulverized zirconia composition; (c) a step of press-molding the pulverized zirconia composition; (d) a step of molding a zirconia composition containing zirconia particles, yttria particles, and a resin; (e) a step of polymerizing a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer; and (f) a step of additive manufacturing of granules containing zirconia particles and yttria particles.

[0062] (a) Slip Casting When a zirconia molded body is produced by a method including a step of slip-casting a slurry containing a zirconia composition after a pulverization treatment, the specific slip-casting method is not particularly limited. For example, a method in which the slurry is poured into a mold and then dried can be employed. The content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, because this facilitates pouring the slurry into the mold, prevents the drying process from taking a long time, and allows the mold to be used more frequently. The slurry may be poured into the mold under normal pressure, but from the viewpoint of production efficiency, it is preferable to pour the slurry into the mold under pressurized conditions.

[0063] (b) Gel Casting When a zirconia molded body is produced by a method including a step of gel-casting a slurry containing a zirconia composition after a pulverization treatment, the specific gel-casting method is not particularly limited. For example, a method can be employed in which the slurry is gelled in a mold to obtain a shaped wet body, and then this is dried. The content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, in order to prevent a long drying time and to suppress the occurrence of cracks during drying. Gelation can be carried out, for example, by adding a gelling agent or by adding a polymerizable monomer and then polymerizing it.

[0064] There is no limitation on the type of gelling agent, and for example, a water-soluble gelling agent can be used, and specifically, agarose, gelatin, etc. can be preferably used. A single gelling agent may be used alone, or two or more types may be used in combination. The amount of gelling agent used is not particularly limited as long as problems such as cracking do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less based on the mass of the slurry after the gelling agent is blended.

[0065] The type of polymerizable monomer is not particularly limited, and examples thereof include (meth)acrylate monomers such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; and (meth)acrylamide monomers such as N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N,N-bis(2-hydroxyethyl) (meth)acrylamide. One type of polymerizable monomer may be used alone, or two or more types may be used in combination. The amount of polymerizable monomer used is not particularly limited as long as problems such as cracking do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less, based on the mass of the slurry after the polymerizable monomer is blended.

[0066] When gelation is carried out by polymerization of a polymerizable monomer, the polymerization is preferably carried out using a polymerization initiator. There are no particular restrictions on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred.

[0067] Specific examples of the photopolymerization initiator include (bis)acylphosphine oxides (including salts), thioxanthones (including salts such as quaternary ammonium salts), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ether compounds, and α-aminoketone compounds. One photopolymerization initiator may be used alone, or two or more may be used in combination. Among these photopolymerization initiators, it is preferable to use at least one selected from the group consisting of (bis)acylphosphine oxides and α-diketones. This allows polymerization (gelation) to occur in both the ultraviolet (including near-ultraviolet) and visible light regions, and in particular, polymerization (gelation) can be sufficiently performed using any light source, such as a laser (e.g., Ar laser, He—Cd laser), or lighting (e.g., halogen lamp, xenon lamp, metal halide lamp, light-emitting diode (LED), mercury lamp, or fluorescent lamp.

[0068] The drying method for drying the shaped wet body is not particularly limited, and examples thereof include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. These may be used alone or in combination. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred because they can suppress the occurrence of cracks during drying.

[0069] There are no particular limitations on the type of mold used in slip casting and gel casting, and for example, porous molds made of plaster, resin, ceramics, etc., and non-porous molds made of metal, resin, etc. can be used.

[0070] (c) Press Molding In the step of press molding the zirconia composition after the pulverization treatment, the specific method of press molding is not particularly limited, and can be performed using a known press molding machine. Specific examples of the press molding method include uniaxial pressing.

[0071] Alternatively, multi-stage molding may be performed. For example, after press-molding the zirconia composition, a cold isostatic pressing (CIP) treatment may be further performed.

[0072] The shape of the molded body is not particularly limited and may be a disk, a rectangular parallelepiped, or a dental product shape (e.g., a crown shape). The molded body may be, for example, a columnar zirconia molded body obtained by filling a mold with a zirconia composition (e.g., granules) and compacting it with a uniaxial press. The higher the surface pressure in the press molding, the higher the density of the molded body. On the other hand, if the density of the zirconia molded body is too high, the zirconia calcined body will become hard. Therefore, the surface pressure in the press molding when producing the zirconia molded body is preferably 30 to 200 MPa. When the surface pressure in the press is 30 MPa or more, the shape retention of the zirconia molded body is excellent, and when it is 200 MPa or less, the density of the zirconia molded body does not increase too much, making it easier to prevent hardening.

[0073] The molded body also includes a molded body densified by a high-temperature pressure treatment such as CIP (Cold Isostatic Pressing). From the same viewpoint as above, the pressure of the CIP is preferably 30 to 200 MPa.

[0074] (d) Molding of a zirconia composition containing a resin When a zirconia molded body is produced by a method including a step of molding a zirconia composition containing zirconia particles, yttria particles, and a resin, the specific method for molding the zirconia composition is not particularly limited, and for example, injection molding, cast molding, extrusion molding, etc. can be used. Furthermore, a method of molding the composition by fusion dynamic molding (FDM), an inkjet method, a powder / binder lamination method, or other additive manufacturing methods (3D printing, etc.) may also be used. Among these molding methods, injection molding and cast molding are preferred, and injection molding is more preferred. The type of resin is not particularly limited, and it is preferable to use the binder described above.

[0075] (e) Polymerization of a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer. Polymerization of a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer polymerizes the polymerizable monomer or oligomer in the composition, thereby hardening the composition. When producing a zirconia molded body using a method including this polymerization step, the specific method is not particularly limited. For example, a method of polymerizing a zirconia composition in a mold or a stereolithography (SLA) method using a zirconia composition can be employed. Among these, the stereolithography (SLA) method (b) is preferred. Stereolithography allows the zirconia molded body to be given a shape corresponding to the desired shape of the final zirconia sintered body at the time of production. Therefore, stereolithography may be particularly suitable when the zirconia sintered body is used as a dental material for dental prostheses, etc. The type of polymerizable monomer is not particularly limited, and may be any of monofunctional polymerizable monomers such as monofunctional (meth)acrylates and monofunctional (meth)acrylamides, and polyfunctional polymerizable monomers such as bifunctional aromatic compounds, bifunctional aliphatic compounds, and trifunctional or higher compounds. One type of polymerizable monomer may be used alone, or two or more types may be used. Among these, it is preferable to use a polyfunctional polymerizable monomer, particularly when a stereolithography method is employed. The oligomer is not particularly limited as long as it is a compound in which two or more of the above polymerizable monomers are bonded and has polymerizability.

[0076] Examples of monofunctional (meth)acrylates include (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and sec-butyl (meth)acrylate. alkyl (meth)acrylates such as acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate; alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic group-containing (meth)acrylates such as benzyl (meth)acrylate and phenyl (meth)acrylate; and (meth)acrylates having a functional group such as 2,3-dibromopropyl (meth)acrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, and 11-(meth)acryloyloxyundecyltrimethoxysilane. Examples of monofunctional (meth)acrylamides include (meth)acrylamide, N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-di-n-propyl(meth)acrylamide, N,N-di-n-butyl(meth)acrylamide, N,N-di-n-hexyl(meth)acrylamide, N,N-di-n-octyl(meth)acrylamide, N,N-di-2-ethylhexyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and N,N-bis(2-hydroxyethyl)(meth)acrylamide.Among these monofunctional polymerizable monomers, (meth)acrylamide is preferred because of its excellent polymerizability, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.

[0077] Examples of the bifunctional aromatic compound include 2,2-bis((meth)acryloyloxyphenyl)propane, 2,2-bis[4-(2-hydroxy-3-acryloyloxy-2-hydroxypropoxy)phenyl]propane, 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (commonly known as "Bis-GMA"), 2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane, 2, Examples of (meth)acrylates include 2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, and 1,4-bis(2-(meth)acryloyloxyethyl)pyromellitate. Among these, Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article. Of the 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propanes, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average number of moles of ethoxy groups added: 2.6, commonly known as "D-2.6E") is preferred.

[0078] Examples of the bifunctional aliphatic compounds include glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of (meth)acrylates include triethylene glycol dimethacrylate (TEGDMA) and UDMA, which are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0079] Examples of tri- or higher functional compounds include (meth)acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacryloyloxy-2,2,6,6-tetra(meth)acryloyloxymethyl-4-oxaheptane. Among these, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetramethacrylate and 1,7-diacryloyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxaheptane are preferred in terms of excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0080] In any of the above methods, the polymerization of the composition is preferably carried out using a polymerization initiator, and the composition preferably further contains a polymerization initiator. There are no particular limitations on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred. Specific examples of photopolymerization initiators are the same as those described above in the explanation of gel casting.

[0081] When a zirconia molded body is produced by stereolithography using the pulverized zirconia composition, the specific method of stereolithography is not particularly limited, and any known method can be appropriately employed for stereolithography. For example, a method can be employed in which a liquid composition is photopolymerized using an optical lithography device with ultraviolet light, a laser, or the like to sequentially form layers having the desired shape, thereby obtaining the desired zirconia molded body.

[0082] To further improve the density of the cured zirconia molded body, the zirconia molded body may be subjected to a humidification treatment followed by a CIP treatment. When press molding is performed, a powder containing zirconia particles may be humidified before press molding, followed by press molding. The humidification method may be any known method, including spraying water with a spray bottle or using a hygrostat or thermo-hygrostat. The moisture content of the humidification treatment varies depending on the average particle size of the zirconia particles and the average particle size of the stabilizer particles, but is preferably greater than 2% by mass, more preferably greater than 3% by mass, even more preferably greater than 4% by mass, and particularly preferably greater than 5% by mass, relative to the mass of the powder before humidification (powder before humidification treatment) and the molded body. It is also preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 11% by mass or less. The moisture content of the powder after humidification can be calculated as a percentage by subtracting the mass of the powder before humidification and the compact from the mass of the wet powder (powder after humidification) and the compact, and dividing the result by the mass of the powder before humidification and the compact. The pressure for the CIP treatment is the same as that described above in the description of press molding.

[0083] (f) Step of additive manufacturing of granules containing zirconia particles and yttria particles When manufacturing granules containing zirconia particles and yttria particles, there are no particular limitations on the specific method. For example, a method can be used in which a slurry is obtained and then dried using a spray dryer to form granules, and the resulting granules can be used for powder additive manufacturing. There are no particular limitations on the powder additive manufacturing method, but examples include a powder bed method, an SLS method (selective laser sintering method), an SLM method (selective laser melting method), an electron beam method, an arc discharge method, and a binder jet method. For methods in which it is preferable to not use organic substances during additive manufacturing, it is preferable not to use organic substances even in the granule manufacturing stage.

[0084] Next, the compact is calcined in a calcination step to obtain the calcined zirconia body of the present invention.

[0085] The calcination temperature (maximum calcination temperature) in the calcination step is preferably 600°C or higher, more preferably 700°C or higher, even more preferably 800°C or higher, and particularly preferably 850°C or higher, from the viewpoint of ensuring a semi-sintered state using the specific zirconia composition described above. Furthermore, the calcination temperature is preferably 1200°C or lower, more preferably 1150°C or lower, even more preferably 1100°C or lower, and particularly preferably 1050°C or lower, from the viewpoint of ensuring workability. That is, the calcination temperature is preferably 600 to 1200°C in the method for producing a zirconia calcined body of the present invention. Furthermore, by using the zirconia composition obtained by the pulverization treatment, the desired zirconia calcined body can be obtained even in a lower temperature range (e.g., about 600 to 900°C) than conventionally.

[0086] The holding time (holding time) at the maximum calcination temperature is not particularly limited as long as it can produce a semi-sintered zirconia calcined body having a half-width within a predetermined range, but is preferably held at the maximum calcination temperature for 30 minutes to 6 hours. Furthermore, the heating rate to the maximum calcination temperature and the heating rate from the maximum calcination temperature are preferably 300°C / min or less. In a preferred embodiment, the heating rate to the maximum calcination temperature when calcining the zirconia molded body of the present invention 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, and is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. A heating rate above the lower limit improves productivity. Furthermore, by keeping the temperature rising rate at or below the above upper limit, the difference in volume between the inside and outside of the zirconia molded body or the zirconia calcined body can be suppressed, and if the zirconia molded body contains an organic substance, rapid decomposition of the organic substance can be suppressed, thereby suppressing cracking and destruction.

[0087] [Zirconia Sintered Body] Next, the zirconia sintered body will be described. The zirconia sintered body is obtained by firing the zirconia calcined body obtained as described above.

[0088] The content of the stabilizer (preferably yttria) in the zirconia sintered body of the present invention is the same as the content of the stabilizer in the zirconia calcined body.

[0089] The zirconia sintered body of the present invention has a half-width of the main peak derived from monoclinic zirconia in the zirconia calcined body within a specific range, and therefore has excellent translucency (in-line light transmittance and total light transmittance) even when sintered by firing at a maximum sintering temperature (e.g., 1550°C) for a holding time (retention time) of 10 minutes or less. Therefore, the zirconia sintered body of the present invention can maintain high translucency, even after sintering for a short time at the maximum sintering temperature (e.g., a holding time of 2 hours at the maximum sintering temperature), at the same level as that achieved by long-term sintering.

[0090] The zirconia sintered body of the present invention may contain a fluorescent agent. The fluorescent agent is the same as the fluorescent agent in the zirconia calcined body. In this specification, regarding the fluorescent agent, "relative to 100% by mass of zirconia contained in the zirconia calcined body" can be read as "relative to 100% by mass of zirconia contained in the zirconia sintered body."

[0091] The zirconia sintered body of the present invention may contain a colorant. Examples of colorants include those similar to those in the zirconia calcined body. The content of the colorant in the zirconia sintered body is not particularly limited and can be adjusted appropriately depending on the type of colorant and the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the content of the colorant, calculated as the oxide of the metal element contained in the colorant, relative to 100% by mass of zirconia contained in the zirconia sintered 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, calculated as the oxide of the metal element contained in 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 even be 0.1% by mass or less, or even 0.05% by mass or less.

[0092] In order to adjust the translucency of the zirconia sintered body of the present invention, the zirconia sintered body of the present invention may contain a translucency adjuster. Examples of the translucency adjuster include the same ones as the translucency adjuster in the zirconia calcined body. The content of the translucency adjuster in the zirconia sintered body is not particularly limited and can be appropriately adjusted depending on the type of translucency adjuster and the application of the zirconia sintered body, but from the viewpoint of being preferably usable as a dental prosthesis, the content is preferably 0.1 mass% or less relative to 100 mass% of zirconia contained in the zirconia sintered body.

[0093] [Method for producing zirconia sintered body] Examples of methods for producing the zirconia sintered body of the present invention include methods for producing a zirconia sintered body by firing the above-mentioned zirconia calcined body. A preferred method includes a step of firing the above-mentioned zirconia calcined body under normal pressure at a maximum sintering temperature of more than 1200°C and not more than 1650°C. Since the zirconia calcined body of the present invention has the predetermined half-width range described above, it is possible to easily produce a zirconia sintered body of the present invention that has excellent translucency, even after sintering for a short period of time, for example, a holding time of 10 minutes or less at the maximum sintering temperature.

[0094] When the zirconia calcined body of the present invention is fired to produce a sintered body, the maximum sintering temperature is preferably set under conditions that allow both translucency and mechanical strength of the zirconia sintered body to be achieved. From the above viewpoints, the maximum sintering temperature is preferably greater than 1200°C, more preferably 1250°C or higher, and even more preferably 1300°C or higher, from the viewpoint of easily obtaining the desired zirconia sintered body under normal pressure. Furthermore, the maximum sintering temperature is preferably 1650°C or lower, more preferably 1600°C or lower, even more preferably 1550°C or lower, particularly preferably 1500°C or lower, and most preferably 1450°C or lower. In one embodiment, a method for producing a zirconia sintered body includes a firing step in which the maximum sintering temperature is greater than 1200°C and 1450°C or lower, because the increased half-width allows firing at a lower temperature than conventional methods. Another embodiment includes a method for producing a zirconia sintered body, which includes a firing step in which the maximum sintering temperature is greater than 1450°C and less than 1650°C when the FWHM is in a narrow range (e.g., 0.18° or more and 0.25° or less). By setting the maximum sintering temperature to be equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, sintering can be sufficiently carried out, and a dense sintered body can be easily obtained. Furthermore, by setting the maximum sintering temperature to be equal to or less than the above-mentioned upper limit, deactivation of the fluorescent agent can be suppressed.

[0095] The holding time at the maximum sintering temperature is preferably 15 minutes or more, more preferably 30 minutes or more, and even more preferably 40 minutes or more. It is also preferably 20 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less. When producing a sintered body by sintering in a short period of time, there is no particular restriction on the sintering time as long as the holding time at the maximum sintering temperature is 10 minutes or less. However, since the desired zirconia sintered body can be obtained efficiently and stably with good productivity, the holding time at the maximum sintering temperature is preferably 10 minutes or less, more preferably 5 minutes or less, even more preferably 3 minutes or less, and particularly preferably 2 minutes or less. The holding time can be 30 seconds or more, 45 seconds or more, or even 1 minute or more.

[0096] When producing a sintered body, the firing time for producing the sintered body can be shortened without reducing the translucency of the zirconia sintered body. In particular, the holding time at the maximum sintering temperature for producing the sintered body can be shortened to 10 minutes or less. This improves production efficiency, and when the zirconia calcined body of the present invention is used for a dental product, it shortens the time from determining the dimensions of the dental product to be used for treatment, cutting the product, and preparing the dental product for treatment, thereby reducing the time burden on patients. It also reduces energy costs.

[0097] The temperature increase rate and temperature decrease rate in the firing step are preferably set so as to shorten the time required for the firing step. For example, the temperature increase rate can be set so as to reach the maximum sintering temperature in the shortest time depending on the performance of the firing furnace. The temperature increase rate to the maximum sintering temperature can be, for example, 10°C / min or more, 50°C / min or more, 100°C / min or more, 120°C / min or more, 150°C / min or more, 200°C / min or more, 250°C / min or more, 300°C / min or more, or 350°C / min or more. The temperature decrease rate is preferably set so as not to cause defects such as cracks in the sintered body. For example, after heating is completed, the sintered body can be allowed to cool at room temperature.

[0098] The calcination and firing in the present invention can be carried out using a firing furnace. There are no particular limitations on the type of firing furnace, and for example, electric furnaces and degreasing furnaces commonly used in industry can be used. A commercially available dental firing furnace (for example, the trade name "Sintra CS" (manufactured by Shenpaz)) can also be used.

[0099] The zirconia sintered body of the present invention can be produced without HIP treatment, but by optionally performing HIP treatment after sintering under normal pressure, it is possible to further improve translucency and mechanical strength. Hereinafter, the sintered body obtained by sintering at the above-mentioned maximum sintering temperature (the sintered body before HIP treatment) will be referred to as the "primary sintered body," and the sintered body after HIP treatment will be referred to as the "HIP-treated sintered body." HIP treatment can be performed using a known hot isostatic pressing (HIP) device.

[0100] When the primary sintered body is subjected to HIP treatment, the HIP pressure is not particularly limited, and since a dense sintered body with high mechanical strength can be obtained, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more. The upper limit of the HIP pressure is not particularly limited, but can be, for example, 400 MPa or less, 300 MPa or less, or even 200 MPa or less.

[0101] When the primary sintered body is subjected to HIP treatment, the temperature rise rate 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 is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. By setting the temperature rise rate at or above the lower limit, productivity is improved.

[0102] When the primary sintered body is subjected to the HIP treatment, the HIP time (the time during which the maximum pressure and temperature are maintained) is not particularly limited, and since a dense zirconia sintered body with high mechanical strength can be obtained, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Moreover, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0103] In the method for producing a zirconia sintered body of the present invention, the pressure medium used in HIPing the primary sintered body is not particularly limited. From the viewpoint of minimizing the effect on zirconia, the pressure medium can be at least one selected from the group consisting of oxygen, oxygen containing 3% hydrogen, air, and an inert gas (e.g., nitrogen, argon, etc.). When the primary sintered body is HIPed in an oxygen-mixed gas atmosphere, the oxygen concentration is not particularly limited, but can be, for example, more than 0% and 20% or less. When an oxygen-mixed gas is used, at least one inert gas (e.g., nitrogen, argon, etc.) can be selected as the gas other than oxygen.

[0104] If the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, black discoloration may occur due to oxygen defects. In this case, to remove the black discoloration, it is preferable to include a heat treatment step (hereinafter also referred to as a "tempering treatment") in the air or in an oxygen-excess atmosphere at 1650°C or less after the HIP treatment. From the viewpoint of efficient heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere. An oxygen-excess atmosphere means that the oxygen concentration is higher than that of the air. The oxygen-excess atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and 100% or less, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%. If the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, black discoloration may occur due to oxygen defects. In this case, to remove the black discoloration, it is preferable to include a heat treatment step (hereinafter also referred to as a "tempering treatment") in the air or in an oxygen-excess atmosphere at 1650°C or less after the HIP treatment. From the viewpoint of efficient heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere. An oxygen-excess atmosphere means that the oxygen concentration is higher than that of the air. The oxygen-excess atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and not more than 100%, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%.

[0105] The zirconia sintered body of the present invention is not particularly limited as long as it exhibits the effects of the present invention, and may be a primary sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment.

[0106] The temperature of the heat treatment in the air or in an oxygen-excess atmosphere can be appropriately changed depending on the aesthetics of the zirconia sintered body (e.g., the shade of a dental prosthesis). In a preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1650°C or less, more preferably 1600°C or less, and even more preferably 1550°C or less, from the viewpoint of the aesthetics of the zirconia sintered body. In another preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1400°C or less, more preferably 1300°C or less, and even more preferably 1200°C or less, from the viewpoint of the aesthetics of the zirconia sintered body. Furthermore, in any embodiment, the temperature of the heat treatment is preferably 500°C or more, more preferably 600°C or more, and even more preferably 700°C or more.

[0107] A general dental zirconia firing furnace can be used for the tempering treatment. Commercially available dental zirconia firing furnaces may be used. Examples of commercially available dental zirconia firing furnaces include Noritake Katana (registered trademark) F-1, F-1N, F-2, and F-2N (all manufactured by SK Medical Electronics Co., Ltd.).

[0108] The zirconia sintered body obtained by firing the zirconia calcined body of the present invention can be suitably used for dental products. Examples of dental products include copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, orthodontic wires, and laminate veneers. By using the zirconia calcined body of the present invention for parts such as implant screws and implant fixtures, discoloration of the gums caused by metals can be suppressed, resulting in excellent aesthetics. Furthermore, while an appropriate method can be selected for the manufacturing method of these products depending on the application, dental products can be obtained, for example, by cutting the zirconia calcined body of the present invention and then firing it. It is preferable to use a CAD / CAM system for the cutting process. The CAD / CAM system is not particularly limited, and known devices can be used. An example of a known device is a CAD / CAM system ("Katana (registered trademark) CAD / CAM system", manufactured by Kuraray Noritake Dental Co., Ltd.).

[0109] The present invention includes embodiments in which all or part of the above-described configurations are combined in various ways within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved.

[0110] Next, the present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way, and many modifications within the technical scope of the present invention are possible by those skilled in the art.

[0111] [Example 1] Commercially available zirconia powder (YO: 0 mol%) and commercially available yttria powder were added to water, and then placed in a bead mill container along with zirconia grinding media (diameter: 0.1 mm). The mixture was milled for 1 hour in the bead mill to obtain a slurry (average particle size: 0.2 μm or less).

[0112] Next, an organic binder was added to the resulting slurry, and the mixture was mixed and stirred. The stirred slurry was dried and granulated using a spray dryer to obtain a powder. This powder was poured into a cylindrical mold, uniaxially pressed at a pressure of 33 MPa, and then subjected to CIP treatment at 190 MPa to obtain a plate- or disk-shaped molded body. The resulting molded body was placed in an electric furnace, heated from room temperature at a rate of 10°C / min, and held at 500°C for 2 hours to degrease the organic components. Thereafter, the temperature was raised at a rate of 10°C / min, and the temperature was maintained at 875°C for 2 hours, and then slowly cooled at a rate of -10°C / min to obtain a zirconia calcined body.

[0113] This zirconia calcined body was then fired under atmospheric pressure at a temperature increase rate of 10°C / min at a maximum sintering temperature of 1,375°C for a holding time of 2 hours to obtain a zirconia sintered body containing 4.5 mol% of yttria. The resulting zirconia sintered body was white.

[0114] [Examples 2 to 14 and Comparative Examples 1 to 3] In Comparative Examples 1 to 3, zirconia calcined bodies and zirconia sintered bodies were produced in the same manner as in Example 1, except that the maximum sintering temperature was changed to 1,550°C and the conditions were further changed to those shown in Table 2. In Examples 2 to 14, zirconia calcined bodies and zirconia sintered bodies were produced in the same manner as in Example 1, except that the conditions were changed to those shown in Table 2. For example, with regard to the yttria content, the amount used was changed so that the yttria content was as shown in Table 2 in Examples 4 to 5 and Comparative Examples 1 to 2. In Examples 2 to 5 and Comparative Examples 1 to 3, the same zirconia raw material (zirconia powder) and yttria raw material (yttria powder) as in Example 1 were used. In Comparative Examples 1 to 3, instead of using a bead mill, the milling process was performed using a ball mill using 2 mm diameter zirconia balls as milling media, and the milling time was changed to that shown in Table 2. In Examples 10 and 11, the milling process was performed using a ball mill similar to that in Example 1, followed by a bead mill using zirconia milling media with a diameter of 0.1 mm. The milling time for each process was changed to the milling time shown in Table 2. In Example 12, 1.5Y zirconia (1.5 mol% YO) was used instead of the commercially available zirconia powder (0 mol% YO), and the yttria content was adjusted to the value shown in Table 2. In Example 13, 1.5Y zirconia (1.5 mol% YO) and 40Y zirconia (40 mol% YO) were used instead of the commercially available zirconia powder (0 mol% YO) and the commercially available yttria powder, and the yttria content was adjusted to the value shown in Table 2. In Example 14, 40Y zirconia (40 mol% YO) was used instead of the commercially available yttria powder, and the yttria content was adjusted to the value shown in Table 2. The 1.5Y zirconia (YO: 1.5 mol%) was produced as follows: Commercially available zirconia powder (YO: 0 mol%) and commercially available yttria powder were added to water so that the yttria content was 1.5 mol% relative to the total mol% of zirconia and yttria.These and zirconia grinding media (diameter: 2 mm) were placed in a ball mill container and milled in a ball mill for 48 hours to obtain a slurry (average particle size: 0.2 μm or less). The resulting slurry was then dried and granulated in a spray dryer to obtain a powder. The resulting powder was then heated and held at 1000°C for 100 hours to obtain a raw material. 40Y zirconia (YO: 40 mol%) was produced as follows: Commercially available zirconia powder (YO: 0 mol%) and commercially available yttria powder were added to water such that the yttria content was 40 mol% relative to the total mol% of zirconia and yttria. These and zirconia grinding media (diameter: 2 mm) were placed in a ball mill container and milled in a ball mill for 48 hours to obtain a slurry (average particle size: 0.2 μm or less). The resulting slurry was then dried and granulated in a spray dryer to obtain a powder. The resulting powder was then heated and held at 1000° C. for 100 hours to obtain a raw material.

[0115] [Example 6] In Example 6, a zirconia calcined body and a zirconia sintered body were produced in the same manner as in Example 1, except that the heating rate was changed to 350°C / min, the maximum sintering temperature was 1580°C, the holding time at the maximum sintering temperature was changed to 2 minutes, the pulverization treatment was performed in a ball mill using zirconia balls with a diameter of 2 mm as pulverization media, and the pulverization time was changed to the time shown in Table 2. In Example 6, the same zirconia raw material (zirconia powder) and yttria raw material (yttria powder) as in Example 1 were used.

[0116] <Evaluation of Half-Width of Monoclinic Crystal of Zirconia Calcined Body> The half-width of the main peak derived from the monoclinic system of the zirconia calcined body obtained in each Example and Comparative Example was determined by analyzing the crystal system of the zirconia calcined body. Specifically, X-ray diffraction was performed using a fully automatic horizontal multipurpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and X-ray analysis integrated software (SmartLab Studio II, manufactured by Rigaku Corporation) under the following conditions, and the half-width of the peak near 2θ = 28.2°, where the peak top of the main peak of the monoclinic system appears, was determined (unit: °). X-ray source: Cu Kα (λ=1.54186 Å) Goniometer length: 300 mm Optical system: Focusing method Detector: High-speed one-dimensional X-ray detector (D / teX Ultra250) Monochromatization: Kβ filter Tube voltage: 40 kV Tube current: 30 mA Scan axis: 2θ / θ Scan speed: 0.2° / min Sampling step: 0.01°

[0117] <Evaluation of the abundance ratio of crystal systems in zirconia calcined body> The abundance ratio f of undissolved yttria in the zirconia calcined bodies obtained in each Example and Comparative Example y , tetragonal crystallinity f t , cubic crystal fraction f c , and the monoclinic fraction f m was determined by analyzing the crystal system in the zirconia calcined body. Specifically, for X-ray diffraction, a fully automatic horizontal multipurpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and X-ray analysis integrated software (SmartLab Studio II, manufactured by Rigaku Corporation) were used to measure under the following conditions, and the area intensity of each peak (peak area intensity I) was determined. X-ray source: Cu Kα (λ = 1.54186 Å) Goniometer length: 300 mm Optical system: focusing method Detector: high-speed one-dimensional X-ray detector (D / teX Ultra250) Monochromatization: Kβ filter Tube voltage: 40 kV Tube current: 30 mA Scan axis: 2θ / θ Scan speed: 0.2 ° / min Sampling step: 0.01 °

[0118] Using the area intensity of each peak, the abundance ratio of undissolved yttria f y(%), and monoclinic crystal ratio f m The results are shown in Table 2.

[0119] <Evaluation of the Average Primary Particle Diameter of Zirconia Calcined Body> The zirconia calcined bodies obtained in each Example and Comparative Example were photographed using an ultra-high resolution field emission scanning electron microscope (product name "SU8200", manufactured by Hitachi High-Tech Corporation) at an acceleration voltage of 5.0 kV, a WD (working distance) of 8.7 mm, and a magnification of 100,000 times to obtain images of the calcined body surface. The obtained images were analyzed to calculate the average particle diameter. Particle diameters were measured using image analysis software (product name "Image-Pro Plus", manufactured by Hakuto Co., Ltd.). The captured SEM images were binarized, and the brightness range was adjusted to clearly show grain boundaries, allowing particles to be recognized from the field of view (area). In the processing file in which the primary particle diameters were recognized, "Diameter" was selected in the "Count / Size Dialog" to determine the distribution (n = 4). Specifically, the arithmetic mean value of the average particle diameter (primary particle diameter) measured in each of four visual fields of one sample using the image analysis software was calculated.

[0120] <Three-Point Bending Strength> The three-point bending strength of the zirconia sintered body was measured in accordance with ISO 6872:2015. A sample measuring 4 mm × 1.2 mm × 15 mm was prepared from the plate-shaped zirconia sintered body of each Example and Comparative Example, and the sample was measured using a universal testing machine under the conditions of a support distance of 12 mm and a crosshead speed of 0.5 mm / min (arithmetic mean value for n = 5). The criteria for the bending strength of the zirconia sintered body were as shown in Table 1 below.

[0121]

[0122] <Total Light Transmittance, Linear Light Transmittance (1.0 mm Thickness)> The total light transmittance and linear light transmittance of a zirconia sintered body at a thickness of 1.0 mm were measured using a turbidity meter ("Haze Meter NDH 4000" manufactured by Nippon Denshoku Industries Co., Ltd.) by transmitting and scattering light generated from a light source through a sample and using an integrating sphere (arithmetic mean value of n = 3). The measurement was performed in accordance with ISO 13468-1:1996 and JIS K 7361-1:1997, and a D65 light source was selected. For the measurement, a disk-shaped zirconia sintered body with a diameter of 30 mm and a thickness of 1.0 mm and mirror-polished on both sides was used as the sample.

[0123] In the table, the yttria content refers to the ratio (mol %) of the number of moles of yttria to the total number of moles of zirconia and yttria. Also, in the table, 28.2° refers to the peak position of the monoclinic system being measured.

[0124] From the above results, it was confirmed that the zirconia calcined body of the present invention has excellent mechanical strength and translucency (in-line light transmittance and total light transmittance). Furthermore, the zirconia calcined body of the present invention has high total light transmittance and excellent translucency even when the thickness of the zirconia sintered body is 1.0 mm, and therefore has excellent aesthetics when used to manufacture dental materials (e.g., dental prostheses). Furthermore, from the results of Example 6, it was confirmed that the zirconia sintered body obtained has excellent translucency even when the holding time at the maximum sintering temperature is 2 minutes. In the comparative examples, the half-width of the main peak derived from the monoclinic system was not within the desired range, and therefore the desired physical properties were not obtained. For example, while the desired mechanical strength was not obtained in Comparative Example 3, Examples 10 and 11 achieved mechanical strengths of 270 MPa or more superior to Comparative Example 3, confirming that the resulting zirconia sintered body has excellent mechanical strength and translucency (in-line light transmittance and total light transmittance).

[0125] The zirconia calcined body of the present invention is useful for producing dental products (particularly for producing dental products for treatment in dental clinics).

Claims

1. A zirconia calcined body comprising zirconia and a stabilizer capable of suppressing a phase transition of the zirconia, the zirconia comprising monoclinic zirconia, and a half-width of a main peak derived from the monoclinic system in a powder X-ray diffraction pattern using CuKα radiation is 0.18° or more.

2. The zirconia calcined body according to claim 1, wherein the stabilizer is yttria.

3. The fraction of yttria not dissolved in zirconia calculated by the following formula (1-1) f y 3. The zirconia calcined body according to claim 2, wherein the content of zirconia in the calcined body is less than 4%. y (%) = I y / (I m +I t +I c +I y )×100 (1-1) (where f y is the abundance rate of yttria not dissolved in zirconia y (%), and in XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the top of the main monoclinic peak appears, and I t represents the integrated intensity of the peak at 2θ = 30.3° where the top of the main peak of the tetragonal system appears, and I c represents the integrated intensity of the peak at 2θ=30.0° where the top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2° where the peak top of the main peak of yttria not dissolved in zirconia appears.) 4. The monoclinic ratio f calculated by the following formula (1-2) m The zirconia calcined body according to claim 2 or 3, wherein (%) is less than 55%. m (%) = I m / (I m +I t +I c +I y )×100 (1-2) (where f m represents the monoclinic crystal ratio (%), and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the top of the main monoclinic peak appears, and I t represents the integrated intensity of the peak at 2θ = 30.3° where the top of the main peak of the tetragonal system appears, and I c represents the integrated intensity of the peak at 2θ=30.0° where the top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2° where the peak top of the main peak of yttria not dissolved in zirconia appears.) 5. The monoclinic ratio f m The zirconia calcined body according to claim 4, wherein (%) is less than 50%.

6. The zirconia calcined body according to claim 1 or 2, which contains primary particles having an average primary particle size of 60 nm or more and less than 250 nm.

7. The zirconia calcined body according to claim 1 or 2, wherein the content of the stabilizer is 2 to 10 mol % based on the total moles of the zirconia and the stabilizer.

8. A method for producing a zirconia calcined body according to claim 1 or 2, comprising: a step of producing a zirconia composition comprising zirconia particles and stabilizer particles capable of suppressing a phase transition of zirconia; a grinding step of grinding the zirconia composition; a shaping step of molding the zirconia composition after the grinding step to obtain a molded body; and a calcining step of calcining the molded body, wherein the zirconia particles comprise monoclinic zirconia particles, and the grinding step (i) uses grinding media having a diameter of less than 1 mm and the grinding time is 10 minutes or more, or (ii) uses grinding media having a diameter of 1 mm or more and the grinding time is more than 40 hours.

9. The method for producing a zirconia calcined body according to claim 8, wherein the calcination temperature in the calcination step is 600 to 1200°C.

10. A method for producing a zirconia sintered body, comprising sintering the zirconia calcined body according to claim 1 or 2 under normal pressure at a maximum sintering temperature of more than 1200°C and not exceeding 1650°C.

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