Zirconia composition, zirconia calcined body, zirconia sintered body, and methods for producing the same

Abstract

The present invention provides: a zirconia composition, a sintered body of which has excellent light transmitting properties, and which is capable of suppressing the opal properties of a sintered body thereof; a zirconia calcined body and a zirconia sintered body, each of which uses this zirconia composition; and a production method which is capable of easily producing this zirconia calcined body or this zirconia sintered body. The present invention relates to a zirconia composition which contains zirconia particles and stabilizer particles that are capable of suppressing a phase transition of zirconia, wherein: the average particle diameter (r1) of the zirconia particles is 1 nm to 60 nm; the average particle diameter (r2) of the stabilizer particles is 1 nm to 60 nm; and the half width of a peak ascribed to the stabilizer as determined by a powder X-ray diffraction pattern obtained using a CuKα ray is 0.05° to 1.0°. The present invention enables the achievement of a zirconia sintered body which has excellent light transmitting properties and low opal properties, since the regularity of the structure of a zirconia sintered body is decreased and wavelength selective reflection and / or transmission is suppressed by using the above-described zirconia composition, thereby suppressing the opal properties.

Description

[Technical Field]

[0001] The present invention relates to a zirconia (zirconium oxide (IV); ZrO2) sintered body that combines high translucency and low opalescence, a calcined body for obtaining the sintered body, a composition, and methods for producing them. [Background technology]

[0002] In recent years, from the viewpoint of aesthetics, zirconia sintered bodies containing yttria have been used as dental materials for dental prostheses, etc., instead of conventional metallic dental prostheses such as silver fillings. These dental prostheses are often produced by molding particles of a zirconia composition or a slurry containing the same into a zirconia molded body having a desired shape such as a disk or a prism, which is then calcined to form a calcined body (mill blank), which is then cut (milled) into the shape of the desired dental prosthesis, and then sintered.

[0003] It has been confirmed that the in-line light transmittance can be improved by making the crystal grain size of a zirconia sintered body small and uniform (see, for example, Patent Document 1). In order to make the crystal grain size of a zirconia sintered body small and uniform, a hot isostatic pressing (HIP) process is required. However, the HIP apparatus used for the HIP process is a special device classified as high-pressure gas production equipment, so it is difficult to say that a zirconia sintered body with high in-line light transmittance can be easily obtained.

[0004] Therefore, zirconia sintered bodies that are excellent in both mechanical strength and translucency without using a HIP apparatus, as well as zirconia molded bodies and zirconia calcined bodies from which such zirconia sintered bodies can be obtained, have also been proposed (Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-214168 [Patent Document 2] International Publication No. 2020 / 179876 [Patent Document 3] International Publication No. 2020 / 179877 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the inventors have found through their investigations that when nanoparticles with an average particle size (average primary particle size) of less than 100 nm (for example, zirconia with an average primary particle size of less than 100 nm) are used as in Patent Documents 2 and 3, simply keeping the crystalline structure small creates a problem in that the uniform structure causes so-called structural color, which appears to be colored by selectively reflecting or transmitting specific wavelengths (hereinafter, this characteristic will be referred to as "opalescence"). Therefore, the use of nanoparticles makes it difficult to achieve an appearance close to the color tone of natural teeth.

[0007] Therefore, an object of the present invention is to provide a zirconia composition that can produce a sintered body having excellent translucency and suppressing the opalescence of the sintered body, a zirconia calcined body using the same, a zirconia sintered body, and a production method that can easily produce these. [Means for solving the problem]

[0008] As a result of intensive research into achieving the above-mentioned object, the present inventors have found that by sintering a zirconia composition comprising zirconia particles and stabilizer particles capable of suppressing a phase transition of zirconia, wherein the zirconia has an average particle size (r1) of 1 to 60 nm, the stabilizer has an average particle size (r2) of 1 to 60 nm, and the half-width of a peak derived from the stabilizer in a powder X-ray diffraction pattern using CuKα rays is 0.05° to 1.0°, the structural regularity of the zirconia sintered body is reduced, wavelength-selective reflection and / or transmission is suppressed, and a zirconia sintered body that combines high translucency and low opalescence can be obtained.Further research led to the completion of the present invention.

[0009] That is, the present invention relates to the following inventions. [1] A composition comprising zirconia particles and stabilizer particles capable of suppressing the phase transition of zirconia, The average particle size (r1) of the zirconia particles is 1 to 60 nm, and the average particle size (r2) of the stabilizer particles is 1 to 60 nm, A zirconia composition, wherein the half width of the peak derived from the stabilizer in the powder X-ray diffraction pattern using CuKα rays is 0.05° to 1.0°. [2] The zirconia composition according to [1], wherein the content of the stabilizer is 2 to 9 mol % based on the total moles of the zirconia and the stabilizer. [3] The zirconia composition according to [1] or [2], wherein the stabilizer is yttria. [4] The zirconia composition according to any one of [1] to [3], wherein the zirconia particles contain a monoclinic system. [5] A composition comprising zirconia and a stabilizer capable of suppressing the phase transition of zirconia, At least a part of the stabilizer is not dissolved in the zirconia, and the monoclinic fraction f m and the local abundance of the stabilizer in particles derived from the stabilizer is 10 to 90 mol %. f m =I 28 / (I 28 +I 30 )*100 (1) (In the formula, f m represents the proportion (%) of monoclinic crystals, and in XRD measurements, I 28 represents the area intensity of the peak near 2θ = 28° where the main peak of the monoclinic system appears, and I 30 represents the integrated intensity of the peak near 2θ=30° where the main peak of the tetragonal or cubic crystal system appears.) [6] The zirconia calcined body according to [5], wherein the content of the stabilizer is 2 to 9 mol % based on the total moles of the zirconia and the stabilizer. [7] The zirconia calcined body according to [5] or [6], wherein the stabilizer is yttria. [8] The zirconia calcined body according to any one of [5] to [7], wherein the OP value calculated using the following formula (2) of a sintered body having a thickness of 1.2 mm after sintering at 900 to 1400°C for 120 minutes is less than 15:

number

[10] The zirconia calcined body according to any one of [5] to [9], wherein a sintered body having a thickness of 1.2 mm has a ΔL*(WB) of 5 or more after sintering at 900 to 1400°C for 120 minutes.

[11] The zirconia calcined body according to any one of [5] to

[10] , wherein a first translucency ΔL1*(WB) of a first sintered body produced by sintering at 1300°C for 120 minutes and a second translucency ΔL2*(WB) of a second sintered body produced by sintering at 1300°C for 10 minutes satisfy the relationship of the following mathematical formula (3): ΔL2*(WB) / ΔL1*(WB)≧0.85 (3)

[12] A method for producing a zirconia calcined body, using the zirconia composition according to any one of [1] to [4].

[13] A composition comprising zirconia and a stabilizer capable of suppressing a phase transition of zirconia, A zirconia sintered body having a stabilizer content of 2 to 9 mol% relative to the total moles of zirconia and stabilizer, a ΔL*(WB) of 5 or more in a sintered body having a thickness of 1.2 mm, and an OP value calculated using the following formula (2) of less than 15.

number

[14] The zirconia sintered body according to

[13] , wherein the stabilizer is yttria.

[15] The zirconia sintered body according to

[13] or

[14] , wherein the particle size distribution on a number basis has at least one peak top in the particle size range of 70 nm or more and 100 nm or less, and contains 3 to 15% particles having a particle size exceeding 100 nm.

[16] A method for producing a zirconia sintered body, using the zirconia composition according to any one of [1] to [4] or the zirconia calcined body according to any one of [5] to

[11] .

[17] A method for producing a zirconia sintered body according to

[16] , comprising a step of sintering at 900 to 1400°C. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a zirconia composition which can produce a sintered body having excellent translucency and which can suppress the opalescence of the sintered body, a zirconia calcined body using the same, a zirconia sintered body, and a production method by which these can be easily produced. According to the present invention, a zirconia sintered body can be provided that can suppress opalescence and has excellent translucency, and therefore can have an appearance that is closer to the color tone of natural teeth. Furthermore, the present invention can provide a zirconia calcined body that can provide such a zirconia sintered body, and a production method that can easily produce the zirconia sintered body. [Brief explanation of the drawings]

[0011] [Figure 1] Particle size chart of the zirconia composition according to Example 1 [Figure 2] XRD (X-Ray Diffraction) chart of the stabilizer in the zirconia composition according to Example 1 [Figure 3] Composition distribution (SEM-EDX) of the crystalline structure of the zirconia calcined body according to Example 1 [Figure 4] Composition distribution (SEM-EDX) of the crystalline structure of the zirconia calcined body according to Comparative Example 2 [Figure 5] Particle size chart of zirconia sintered bodies according to Example 1 and Comparative Example 2 DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention provides a zirconia composition comprising zirconia particles and stabilizer particles capable of suppressing the phase transition of zirconia, wherein the zirconia has an average particle size (r1) of 1 to 60 nm, the stabilizer has an average particle size (r2) of 1 to 60 nm, and the peak attributable to the stabilizer in a powder X-ray diffraction pattern using CuKα radiation has a half-width of 0.05° to 1.0°. By using this zirconia composition, a zirconia sintered body having low opalescence and excellent translucency can be obtained. Furthermore, the zirconia sintered body obtained using the zirconia composition of the present invention exhibits excellent translucency even when sintered for a short period of time.

[0013] The present invention also provides a method for producing a zirconia-based composite material comprising: zirconia; and a stabilizer capable of suppressing the phase transition of the zirconia; wherein at least a portion of the stabilizer is not solid-dissolved in the zirconia; and wherein the monoclinic fraction f is expressed by the following mathematical formula (1): m The present invention includes a zirconia calcined body having a zirconia content of 50 to 98 mol % and a stabilizer content of 10 to 90 mol % locally. By using the zirconia calcined body, it is possible to obtain a zirconia sintered body having excellent translucency and suppressed opalescence. f m =I 28 / (I 28 +I 30 )*100 (1) (In the formula, f m represents the proportion (%) of monoclinic crystals, and in XRD measurements, I 28represents the area intensity of the peak near 2θ = 28° where the main peak of the monoclinic system appears, and I 30 represents the integrated intensity of the peak near 2θ=30° where the main peak of the tetragonal or cubic crystal system appears.)

[0014] First, the zirconia composition will be described below.

[0015] [Zirconia composition] The zirconia composition of the present invention contains zirconia particles and stabilizer particles capable of suppressing the phase transition of zirconia.

[0016] It is preferable to prepare and use the zirconia particles and the stabilizer particles capable of suppressing the phase transition of zirconia separately, since they have desired properties, such as at least a portion of the stabilizer capable of suppressing the phase transition of zirconia (hereinafter also referred to as "stabilizer") not being solid-dissolved in zirconia. Furthermore, it is preferable that the zirconia particles contain a monoclinic system, from the viewpoint of suppressing opalescence in a sintered body obtained using the zirconia composition and of maintaining excellent translucency even when a zirconia calcined body using the zirconia composition is sintered for a short period of time. By separately preparing and using each particle, when combined with other technical features in the process of producing a zirconia composition, a zirconia calcined body, or a zirconia sintered body, the crystallinity of the zirconia composition can be sufficiently increased, and the stabilizer dissolves in zirconia and initiates phase transition around the stabilizer, making it difficult for the sintered crystal structure to have a structure consisting of uniformly small particles. This is thought to reduce the structural regularity of the zirconia sintered body, suppress wavelength-selective reflection and / or transmission, and produce a zirconia sintered body that combines high translucency with low opalescence.

[0017] The average particle size (r1) of the zirconia particles contained in the composition of the present invention and the average particle size (r2) of the stabilizer particles capable of suppressing the phase transition of zirconia are both 60 nm or less, preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 35 nm or less. When r1 and r2 are 60 nm or less, the crystalline structure after sintering is small, improving translucency. Furthermore, r1 and r2 are both 1 nm or more, preferably 2 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. When r1 and r2 are 1 nm or more, aggregation of primary particles is suppressed. The range may be a combination of any of these values. For example, r1 and r2 are both 1 to 60 nm, preferably 2 to 50 nm, more preferably 5 to 40 nm, and even more preferably 10 to 35 nm. r1 and r2 are average primary particle sizes, and may be the same or different as long as they satisfy the above range. The average primary particle size can be measured after pulverization. The method for measuring the average primary particle diameter is not particularly limited, but can be measured, for example, by observing with a high-magnification electron microscope. Specifically, the method described in the Examples below can be mentioned.

[0018] In one embodiment, a smaller r2 and a larger r1 are preferable because the opalescence decreases. In particular, when the ratio (r2 / r1) is less than 0.5, the opalescence tends to decrease, so it is preferable that r2 is small and r1 is large. On the other hand, even in an embodiment in which r1 and r2 are close to each other, if the content of the stabilizer is low, the frequency of the stabilizer in the zirconia composition decreases, the crystal structure becomes non-uniform, and the opalescence can be reduced, which is preferable. An example of an embodiment in which r1 and r2 are close to each other is a zirconia composition in which the ratio (r2 / r1) is 0.5 to 2 and the stabilizer content is 2.0 to 6.0 mol% based on the total moles of zirconia and stabilizer. In the above embodiment, the ratio (r2 / r1) may be 0.55 to 1.5. In the above embodiment, the stabilizer content may be 2.0 to 5.5 mol% based on the total moles of zirconia and stabilizer.

[0019] The shape of the peak in the particle size distribution of the stabilizer particles contained in the zirconia composition of the present invention is preferably a bimodal peak (two peaks), a tailing peak with a single peak and a shoulder (e.g., a tailing peak with a peak on the smaller particle size side and a shoulder on the larger particle size side), or a leading peak with a single peak and a shoulder (e.g., a leading peak with a peak on the larger particle size side and a shoulder on the smaller particle size side). Furthermore, within the range of the average particle size (r2) described above, a stabilizer with a larger particle size is preferred because the stabilizer and zirconia do not completely dissolve in solid solution, resulting in reduced opalescence. The particle size distribution of the stabilizer particles can be measured by the method described in the Examples below.

[0020] The ratio (r2 / r1) of the average particle size (r1) of zirconia particles to the average particle size (r2) of stabilizer particles capable of suppressing the phase transition of zirconia is preferably 0.1 to 10, more preferably 0.2 to 6, from the viewpoint of forming a crystal structure that suppresses opalescence. By setting the ratio (r2 / r1) to 0.1 or more, the range of grain growth occurring as the stabilizer dissolves in the zirconia particles can be restricted, resulting in a sintered body with a crystal grain size that is less likely to exhibit opalescence. Furthermore, by setting the ratio (r2 / r1) to 10 or less, uneven distribution of the stabilizer can be avoided, and a decrease in translucency (ΔL*(WB)) due to localized grain growth can be suppressed, which is preferable.

[0021] In order to ensure that sintering proceeds almost uniformly, resulting in a uniform structure after sintering and preventing the occurrence of opalescence, it is preferable that the stabilizer is not completely dissolved in the zirconia in the zirconia composition of the present invention. The phrase "the stabilizer is not completely dissolved in the zirconia" means that at least a portion of the stabilizer is not dissolved in the zirconia. The fact that at least a portion of the stabilizer is not dissolved in the zirconia can be confirmed, for example, by an X-ray diffraction (XRD) pattern using CuKα radiation obtained using the zirconia composition. When a peak attributable to the stabilizer is observed in the XRD pattern of the zirconia composition, it can be said that the stabilizer is present in the zirconia composition but is not dissolved in the zirconia.

[0022] Furthermore, from the viewpoint of forming a crystal structure that reduces opalescence while improving the translucency of the sintered body, the peak derived from the stabilizer in the XRD pattern has a half-width of 1.0° or less, preferably 0.8° or less, and more preferably 0.6° or less. From the viewpoint of the composition distribution of the stabilizer, the half-width is 0.05° or more, preferably 0.1° or more, and more preferably 0.2° or more. As long as it is within the range of 0.05° to 1.0°, it may be a range formed by combining any of these values. For example, the half-width is preferably 0.1° to 0.8°, and more preferably 0.2° to 0.6°. By combining the range of the average particle size (r1) of the zirconia particles, the range of the average particle size (r2) of the stabilizer particles, and the half-value width of the peak derived from the stabilizer of 0.05° to 1.0°, the monoclinic fraction f m can be set to 50% or more and 98% or less, and the ΔL*(WB) of the zirconia sintered body can be set to 5 or more, and the OP value calculated using the formula (2) can be set to less than 15. By setting the half-value width within the above range, the monoclinic fraction f mis 50 to 98%, the amount of the stabilizer locally present in particles derived from the stabilizer can be adjusted to a desired range, and the OP value calculated using the formula (2) in the zirconia sintered body after sintering the zirconia calcined body can be made less than 15. Here, the half-width in this specification refers to the width (unit: °) of the peak at half the intensity of the peak derived from the stabilizer in the powder X-ray diffraction pattern using CuKα radiation. The half-width can be measured under the same conditions as those described in the Examples below, for example.

[0023] The content of the stabilizer in the zirconia composition of the present invention is preferably 2 mol% or more, more preferably 3 mol% or more, and even more preferably 4 mol% or more, based on the total moles of zirconia (zirconium (IV) oxide; ZrO) and stabilizer. A content of 2 mol% or more is preferable in that the crystal form contained in the sintered body contains more cubic crystals, thereby improving translucency. The content of the stabilizer is preferably 9 mol% or less, more preferably 8.5 mol% or less, and even more preferably 8 mol% or less. When the content is 9 mol% or less, the proportion of cubic crystals in the encapsulated crystal system is not too high, which is preferable because it is easy to suppress grain growth, the crystal structure does not become too large, and a decrease in translucency is suppressed. The content of the stabilizer may be within any combination of these ranges. For example, the content of the stabilizer is preferably 2 to 9 mol %, more preferably 3 to 8 mol %.

[0024] The stabilizer is preferably one capable of forming partially stabilized zirconia, such as calcium oxide (CaO), magnesium oxide (MgO), yttria (Y2O3), cerium oxide (CeO2), scandium oxide (Sc2O3), niobium oxide (Nb2O5), lanthanum oxide (La2O3), erbium oxide (Er2O3), and praseodymium oxide (Pr6O 11, PrO3), samarium oxide (SmO3), europium oxide (EuO3), and thulium oxide (TmO3). Yttria is preferred because, when combined with the above-mentioned configuration of the predetermined half-width, etc., the sintered body has excellent light transmittance even when sintered for a short time.

[0025] The content of the stabilizer in the entire composition can be determined by common analytical methods, such as inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis (XRF), and energy dispersive or wavelength dispersive X-ray analysis associated with a scanning electron microscope (SEM-EDX or SEM-WDX).

[0026] The zirconia composition of the present invention may contain additives (excluding the stabilizer) such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (Al2O3), titanium oxide (TiO2), silica (SiO2), etc., as needed. These components may be used alone or in combination of two or more. 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, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Er. Examples of the composite pigment include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, and (Co,Zn)Al2O4.

[0027] The zirconia composition of the present invention may contain a fluorescent agent. When the zirconia composition contains a fluorescent agent, the zirconia sintered body becomes fluorescent. 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 such 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 or more of these metal elements. 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.

[0028] The content of the fluorescent agent in the zirconia composition is not particularly limited and can be adjusted appropriately 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% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, calculated as the oxide of the metal element contained in the fluorescent agent, relative to 100% by mass of zirconia contained in the zirconia composition. Furthermore, the fluorescent agent content is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, calculated as the oxide of the metal element contained in the fluorescent agent. By setting the content at or above the lower limit, the fluorescence is comparable to that of natural human teeth. By setting the content at or below the upper limit, the decrease in translucency and mechanical strength can be suppressed.

[0029] The zirconia composition of the present invention may contain a binder. Examples of binders include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic binders, wax-based binders, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose. 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 5% by mass or less, and even more preferably 3% by mass or less, relative to 100% by mass of zirconia.

[0030] [Method of producing zirconia composition] The zirconia composition of the present invention preferably includes a step of producing zirconia particles, a step of producing stabilizer particles, and a step of producing a powder containing zirconia-based particles. Hereinafter, particles containing zirconia particles and stabilizer particles capable of suppressing the phase transition of zirconia will be referred to as "zirconia-based particles" because the amount of zirconia particles is sufficiently greater than the amount of stabilizer particles.

[0031] Method for producing zirconia particles and stabilizer particles The method for preparing the zirconia particles contained in the zirconia composition of the present invention is not particularly limited, and can be, for example, a breakdown process in which coarse particles are pulverized or crushed to produce fine particles, or a building-up process in which atoms or ions are synthesized through a nucleation and growth process. The method for preparing zirconia particles will be described below using examples. The method for preparing zirconia particles can also be used for preparing stabilizer particles, unless otherwise specified.

[0032] The breakdown process can be carried out by pulverizing using, for example, a ball mill or a bead mill. The breakdown process can be used as a method for producing zirconia particles. On the other hand, the breakdown process is preferred as a method for producing stabilizer particles because it enhances the crystallinity of yttria and makes it easy to adjust the half-width of the stabilizer-derived peak to a desired range. In the breakdown process, stabilizer particles are pulverized to obtain particles with a desired average particle size. It is preferable to use fine-sized pulverizing media for pulverization. For example, it is preferable to use pulverizing media of 100 μm or less. Also, the desired ΔL * In order to obtain (WB), it is preferable to crush the coarse particles and then classify the resulting zirconia particles from the viewpoint of adjusting r1 and r2. Known methods and devices can be used for classification. Known methods include, for example, elutriation (water elutriation) utilizing the difference in sedimentation velocity due to particle size-dependent dispersibility, and sedimentation can be accelerated using a centrifuge. Known devices include, for example, porous membranes (membrane filters with pore sizes of 100 nm, etc.), classification devices (wet classification devices, dry classification devices), etc. In particular, in the method for producing stabilizer particles, it is preferable to use a solid stabilizer (e.g., yttria) as a raw material, because this makes it easier to increase the crystallinity of the zirconia composition and to adjust the half-width of the peak derived from the stabilizer in the XRD pattern to the desired range of the present invention.

[0033] On the other hand, examples of build-up processes include gas-phase pyrolysis, in which an oxide is precipitated by thermal decomposition while vaporizing an oxyacid salt of a metal ion or an organometallic compound; a gas-phase reaction method, in which synthesis is carried out by a gas-phase chemical reaction between a gaseous metal compound with a high vapor pressure and a reactant gas; an evaporation concentration method, in which a raw material is heated and vaporized and then rapidly cooled in an inert gas at a predetermined pressure to condense the vapor into fine particles; a melt method, in which a molten liquid is cooled into small droplets and solidified to form a powder; a solvent evaporation method, in which a solvent is evaporated to increase the concentration in the liquid to a supersaturated state, and then precipitates; and a precipitation method, in which the solute concentration is supersaturated by reaction with a precipitant or hydrolysis, and then sparingly soluble compounds such as oxides and hydroxides are precipitated through a nucleation-growth process.

[0034] Precipitation methods are further subdivided into homogeneous precipitation, in which a precipitant is produced in a solution by a chemical reaction, eliminating localized unevenness in the precipitant concentration; coprecipitation, in which multiple metal ions coexisting in a solution are simultaneously precipitated by adding a precipitant; hydrolysis, in which an oxide or hydroxide is obtained by hydrolysis from a metal salt solution or an alcohol solution of a metal alkoxide, etc.; and solvothermal synthesis, in which an oxide or hydroxide is obtained from a high-temperature, high-pressure fluid. Solvothermal synthesis is further subdivided into hydrothermal synthesis, in which water is used as a solvent, and supercritical synthesis, in which a supercritical fluid such as water or carbon dioxide is used as a solvent. In the present invention, it is preferable not to use a coprecipitation method using zirconia and a stabilizer, since the zirconia particles and stabilizer particles each have the desired average particle diameters (r1 and r2). In addition, it is preferable that the stabilizer particles (e.g., yttria particles) are not produced in a liquid phase in order to enhance the crystallinity of the zirconia composition. If the stabilizer particles are produced in a liquid phase, the crystallinity cannot be sufficiently enhanced, and the half-width of the peak derived from the stabilizer in the XRD pattern cannot be set within the desired range of the present invention.

[0035] For any build-up process, it is preferable to increase the precipitation rate to obtain finer zirconia particles. *The resulting zirconia particles are preferably classified in order to obtain a desired WB and linear light transmittance. Classification can be performed using known methods and devices. Examples of known devices include porous membranes (e.g., membrane filters with pores of 100 nm) and classification devices (wet classification devices, dry classification devices).

[0036] The zirconium source used in the build-up process may be, for example, a nitrate, an acetate, a chloride, an alkoxide, etc. Specific examples of the zirconium source include zirconium oxychloride, zirconium acetate, and zirconyl nitrate.

[0037] The zirconia particles may be used in the step of producing a powder containing zirconia-based particles in the form of a slurry containing zirconia particles without drying, as long as the average particle size of the zirconia particles is within the desired range when produced by a method such as a building-up process. The method for preparing the slurry containing zirconia particles is not particularly limited, and may be, for example, one obtained through the above-mentioned breakdown process or building-up process, or a commercially available product.

[0038] In the method for producing the zirconia composition of the present invention, the average particle size (r1 and r2) can be controlled, for example, by a milling step. Zirconia and stabilizer may be milled separately to obtain zirconia particles and stabilizer particles having the desired average particle size (r1 and r2). When milling simultaneously, the energy of the milling may promote solid dissolution of the stabilizer, so a production method that involves fewer mixing and milling steps is preferable. The milling method is not particularly limited, and may include media milling such as a ball mill or bead mill, or medialess milling such as wet JET or dry JET milling.

[0039] As described above, the zirconia particles and stabilizer particles can be controlled by classification, pulverization, etc. depending on the production method so that the respective particles have the desired average particle diameters (r1 and r2).

[0040] In the pulverization step, additives may be added to increase pulverization efficiency and suppress solid solution formation, such as dispersants, emulsifiers, antifoaming agents, and plasticizers.

[0041] Examples of dispersants include ammonium polycarboxylate (e.g., triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic acid ester copolymer, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (e.g., polyoxyethylene alkyl ether phosphate esters such as polyoxyethylene lauryl ether phosphate esters), nonionic surfactants, oleic glycerides, amine surfactants, and oligosaccharide alcohols.

[0042] Examples of emulsifiers include alkyl ethers, phenyl ethers, sorbitan derivatives, and ammonium salts.

[0043] Examples of the antifoaming agent include alcohol, polyether, polyethylene glycol, silicone, and wax. Examples of the plasticizer include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0044] -Method of manufacturing powder containing zirconia-based particles A powder (mixed powder) containing zirconia-based particles can be obtained by mixing zirconia particles with stabilizer particles capable of suppressing the phase transition of zirconia. The method for mixing the zirconia particles with the stabilizer particles capable of suppressing the phase transition of zirconia is not particularly limited, and examples thereof include wet mixing and dry mixing. As described above, the zirconia particles may be in the form of a slurry containing zirconia particles, and the stabilizer particles may be in the form of a slurry containing stabilizer particles. Therefore, in some embodiments, a method is provided in which a slurry containing zirconia particles is mixed with a slurry containing stabilizer particles to obtain a slurry containing zirconia-based particles, and the slurry containing zirconia-based particles is then dried to obtain a powder containing zirconia-based particles; or a method is provided in which zirconia particles (powder) are mixed with a slurry containing stabilizer particles to obtain a slurry containing zirconia-based particles, and the slurry containing zirconia-based particles is then dried to obtain a powder containing zirconia-based particles. The method for preparing the powder containing zirconia-based particles is not particularly limited, and the powder containing zirconia-based particles is preferably obtained by drying the above-mentioned slurry containing zirconia-based particles, since this method allows for the production of a more uniform zirconia sintered body with excellent physical properties. The slurry to be dried here may further contain a fluorescent agent and / or a colorant and / or a translucency adjuster.

[0045] The drying method is not particularly limited, and can be, for example, spray drying, supercritical drying, freeze drying, hot air drying, reduced pressure drying, etc. Among these, any of spray drying, supercritical drying, and freeze drying is preferred, any of spray drying and supercritical drying is more preferred, and spray drying is even more preferred, because it can suppress aggregation of particles during drying and can produce a denser zirconia sintered body.

[0046] The slurry containing zirconia-based particles to be dried may be a slurry in which the dispersion medium is water, but it is preferable to use a slurry in which the dispersion medium is other than water, such as an organic solvent, because this can suppress aggregation of particles during drying and enable the production of a denser zirconia sintered body.

[0047] Examples of organic solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, 2-methoxyethanol, 2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol, diethylene glycol monobutyl ether, and glycerin; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, diethyl ether, diisopropyl ether, 1,4-dioxane, and dimethoxyethane (including modified ethers such as propylene glycol monomethyl ether acetate (commonly known as "PGMEA") (preferably ether-modified ethers and / or ester-modified ethers, more preferably ether-modified alkylene glycols and / or ester-modified alkylene glycols)); esters such as ethyl acetate and butyl acetate; hydrocarbons such as hexane and toluene; and halogenated hydrocarbons such as chloroform and carbon tetrachloride. These organic solvents may be used alone or in combination of two or more. Among these, taking into consideration both safety to living organisms and ease of removal, the organic solvent is preferably a water-soluble organic solvent, and specifically, ethanol, 2-propanol, 2-methyl-2-propanol, 2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol, propylene glycol monomethyl ether acetate, acetone, and tetrahydrofuran are more preferred.

[0048] Furthermore, particularly when spray drying is employed, it is preferable that the dispersion medium of the slurry containing zirconia-based particles to be dried contains a liquid having a surface tension of 50 mN / m or less at 25° C., since this can prevent the particles from aggregating during drying and allows for the production of a denser zirconia sintered body. From this perspective, the surface tension of the liquid is preferably 40 mN / m or less, and more preferably 30 mN / m or less.

[0049] The surface tension at 25°C can be determined using, for example, the value described in the Handbook of Chemistry and Physics. For liquids not described therein, the value described in International Publication No. 2014 / 126034 can be used. For liquids not described in any of these publications, the value can be determined using known measurement methods, such as the hanging ring method or the Wilhelmy method. The surface tension at 25°C is preferably measured using an automatic surface tensiometer "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. or a "SIGMA702" manufactured by KSV INSTRUMENTS LTD.

[0050] As the liquid, an organic solvent having the above-mentioned surface tension can be used. As the organic solvent, any of the above-mentioned organic solvents having the above-mentioned surface tension can be used, but at least one selected from the group consisting of methanol, ethanol, 2-methoxyethanol, 1,4-dioxane, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol is preferred, and at least one selected from the group consisting of methanol, ethanol, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol is more preferred, because it can suppress aggregation of particles during drying and can produce a denser zirconia sintered body.

[0051] The content of the liquid in the dispersion medium is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, because this can suppress aggregation of particles during drying and allow a denser zirconia sintered body to be obtained.

[0052] A slurry containing a dispersion medium other than water can be obtained by substituting the dispersion medium for a slurry containing water (hereinafter also referred to as "water slurry"). There are no particular limitations on the method for substituting the dispersion medium, and for example, a method can be employed in which a dispersion medium other than water (such as an organic solvent) is added to a slurry containing water as the dispersion medium, and then the water is distilled off. When distilling off the water, part or all of the dispersion medium other than water may be distilled off together. The addition of the dispersion medium other than water and the distillation off of the water may be repeated multiple times. Alternatively, a method can be employed in which a dispersion medium other than water is added to a slurry containing water as the dispersion medium, and then the dispersoid is precipitated. Furthermore, the dispersion medium of a slurry containing water as the dispersion medium may be substituted with a specific organic solvent, and then further substituted with another organic solvent.

[0053] The fluorescent agent may be added after replacing the dispersion medium, but is preferably added before replacing the dispersion medium, because this allows for the production of a more uniform zirconia sintered body with excellent physical properties. Similarly, when a colorant and / or a translucency adjuster is contained in the slurry, these may be added after replacing the dispersion medium, but are preferably added before replacing the dispersion medium, because this allows for the production of a more uniform zirconia sintered body with excellent physical properties.

[0054] The zirconia-based particle-containing slurry to be dried may be one that has been subjected to a dispersion treatment using heat or pressure, such as reflux treatment or hydrothermal treatment. The zirconia-based particle-containing slurry to be dried may also be one that has been subjected to a mechanical dispersion treatment using a roll mill, colloid mill, high-pressure jet disperser, ultrasonic disperser, vibration mill, planetary mill, bead mill, or the like. Only one of the above-mentioned treatments may be used, or two or more of them may be used.

[0055] The slurry containing zirconia-based particles to be dried may further contain one or more of other components such as a binder, a dispersant, an emulsifier, an antifoaming agent, a pH adjuster, a lubricant, etc. By containing such other components (particularly a binder, a dispersant, an antifoaming agent, etc.), it is possible to suppress aggregation of particles during drying, and in some cases it is possible to obtain a denser zirconia sintered body.

[0056] Examples of the dispersant, emulsifier, and antifoaming agent include the same as those exemplified as additives in the grinding step of the above-mentioned method for producing zirconia particles.

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

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

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

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

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

[0062] The powder containing zirconia-based particles obtained as described above can be used as a zirconia composition containing zirconia particles and stabilizer particles capable of suppressing the phase transition of zirconia. In the present invention, the zirconia composition may be subjected to a molding process to form a molded product. The molded body is one that has been molded by applying an external force to a powder containing zirconia-based particles, and since it is a product before sintering, it means one that is not necked (adhered). The type of the molding step is not particularly limited, but the molding step is preferably performed in the following manner, since it allows the zirconia molded body of the present invention, and further the zirconia calcined body and zirconia sintered body of the present invention to be easily obtained: (i) slip-casting a slurry containing zirconia-based particles; (ii) gel-casting a slurry containing zirconia-based particles; (iii) press-molding the powder containing zirconia-based particles; (iv) molding a composition comprising zirconia-based particles and a resin; and (v) polymerizing the composition comprising the zirconia-based particles and the polymerizable monomer; It is preferable that the method is at least one of the above, and that the method has a molding step of molding zirconia particles, a polyol, and a binder to obtain a zirconia molded body.

[0063] (i) Slip casting When a zirconia molded body is produced by a method including a step of slip-casting a slurry containing zirconia-based particles, the specific method of slip-casting is not particularly limited. For example, a method can be employed in which a slurry containing zirconia-based particles is poured into a mold and then dried.

[0064] The content of the dispersion medium in the slurry containing the zirconia-based particles 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 allows the slurry to be easily poured into a mold, prevents the drying process from taking a long time, and enables the mold to be used more frequently.

[0065] 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 under pressurized conditions. There are no particular limitations on the type of mold used in slip casting, and for example, porous molds made of gypsum, resin, ceramics, etc. can be used. Porous molds made of resin or ceramics are excellent in terms of durability.

[0066] The zirconia-based particle-containing slurry used in slip casting may further contain one or more of the above-mentioned other components, such as binders, plasticizers, dispersants, emulsifiers, antifoaming agents, pH adjusters, and lubricants.

[0067] (ii) Gel casting When a zirconia molded body is produced by a method including a step of gel-casting a slurry containing zirconia-based particles, the specific method of gel-casting is not particularly limited. For example, a method can be employed in which a shaped wet body is obtained by gelling a slurry containing zirconia particles and a fluorescent agent in a mold, and then the obtained wet body is dried.

[0068] The content of the dispersion medium in the slurry containing the zirconia-based particles 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 can prevent drying from taking a long time and can also suppress the occurrence of cracks during drying.

[0069] The gelation may be carried out, for example, by adding a gelling agent, or by adding a polymerizable monomer and then polymerizing it. There are no particular limitations on the type of mold used, and for example, a porous mold made of gypsum, resin, ceramics, etc., or a non-porous mold made of metal, resin, etc., can be used.

[0070] 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. From the viewpoint of suppressing the occurrence of cracks during sintering, the amount of gelling agent used is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, based on the mass of the slurry after the gelling agent is blended.

[0071] The type of polymerizable monomer is not particularly limited, and examples thereof include 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, erythritol mono(meth)acrylate, N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N,N-bis(2-hydroxyethyl) (meth)acrylamide, etc. One type of polymerizable monomer may be used alone, or two or more types may be used in combination.

[0072] From the viewpoint of suppressing the occurrence of cracks during sintering, the amount of polymerizable monomer used is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, based on the mass of the slurry after the polymerizable monomer has been blended.

[0073] 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.

[0074] Specific examples of photopolymerization initiators 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 or more photopolymerization initiators may be used alone or 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. In particular, polymerization (gelation) can be sufficiently achieved using any light source, including lasers such as Ar lasers and He-Cd lasers; and lighting such as halogen lamps, xenon lamps, metal halide lamps, light-emitting diodes (LEDs), mercury lamps, and fluorescent lamps.

[0075] Of the above (bis)acylphosphine oxides, examples of the acylphosphine oxides include 2,4,6-trimethylbenzoyldiphenylphosphine oxide (commonly known as "TPO"), 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide, 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide, 2,3,5,6-tetramethylbenzoyldiphenylphosphine oxide, benzoyldi(2,6-dimethylphenyl)phosphonate, sodium salt of 2,4,6-trimethylbenzoylphenylphosphine oxide, potassium salt of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and ammonium salt of 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0076] Of the (bis)acylphosphine oxides, examples of the bisacylphosphine oxides include bis(2,6-dichlorobenzoyl)phenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, bis(2,6-dimethoxybenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and bis(2,3,6-trimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide. Furthermore, compounds described in JP-A No. 2000-159621 can also be used.

[0077] Among these (bis)acylphosphine oxides, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and the sodium salt of 2,4,6-trimethylbenzoylphenylphosphine oxide are preferred.

[0078] Examples of α-diketones include diacetyl, benzyl, camphorquinone, 2,3-pentadione, 2,3-octadione, 9,10-phenanthrenequinone, 4,4′-oxybenzyl, acenaphthenequinone, etc. Among these, camphorquinone is preferred, particularly when a light source in the visible light region is used.

[0079] The zirconia-based particle-containing slurry used in gel casting may also contain one or more of the above-mentioned other components, such as binders, plasticizers, dispersants, emulsifiers, antifoaming agents, pH adjusters, and lubricants, as in the case of slurries used in slip casting.

[0080] 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.

[0081] (iii) Press molding When a zirconia molded body is produced by a method including a step of press-molding a powder containing zirconia-based particles, the specific press-molding method is not particularly limited, and can be performed using a known press molding machine. Specific press-molding methods include, for example, uniaxial pressing. Furthermore, in order to increase the density of the resulting zirconia molded body, it is preferable to further perform cold isostatic pressing (CIP) treatment after uniaxial pressing.

[0082] The powder containing the zirconia-based particles used for press molding may further contain one or more of the above-mentioned other components such as binders, plasticizers, dispersants, emulsifiers, antifoaming agents, pH adjusters, lubricants, etc. These components may be blended when preparing the powder.

[0083] (iv) Molding of a composition containing a resin When a zirconia molded body is produced by a method including a step of molding a composition containing zirconia-based particles and a resin, the specific method for molding the composition is not particularly limited, and examples thereof include injection molding, cast molding, and extrusion molding. Alternatively, the composition may be molded by fusion dynamic molding (FDM), or by an additive manufacturing method (e.g., 3D printing) such as an inkjet method or a powder / binder lamination method. Among these molding methods, injection molding and cast molding are preferred, with injection molding being more preferred.

[0084] The type of the resin is not particularly limited, and one that functions as a binder can be preferably used. Specific examples of the resin include paraffin wax, polyvinyl alcohol, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, atactic polypropylene, methacrylic resin, and fatty acids such as stearic acid. These resins may be used alone or in combination of two or more.

[0085] The composition containing the zirconia-based particles and resin may further contain one or more of the other components, such as the plasticizer, dispersant, emulsifier, antifoaming agent, pH adjuster, and lubricant, as described above.

[0086] (v) Polymerization of a composition containing a polymerizable monomer By polymerizing a composition containing zirconia-based particles and a polymerizable monomer, the polymerizable monomer in the composition can be polymerized and hardened. When producing a zirconia molded body using a method including this polymerization step, the specific method is not particularly limited. For example, (a) a method of polymerizing a composition containing zirconia-based particles and a polymerizable monomer in a mold; or (b) a stereolithography (SLA) method using a composition containing zirconia-based particles and a polymerizable monomer can be employed. Among these, the stereolithography method (b) is preferred. The stereolithography method 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, the stereolithography method may be particularly suitable when the zirconia sintered body of the present invention is used as a dental material for dental prostheses, etc.

[0087] The type of polymerizable monomer in the composition containing the zirconia-based particles and the 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 functional 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, especially when a stereolithography method is employed.

[0088] Examples of the monofunctional (meth)acrylate 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. Examples of the acrylate include 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 functional groups such as 2,3-dibromopropyl (meth)acrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, and 11-(meth)acryloyloxyundecyltrimethoxysilane.

[0089] 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.

[0090] 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.

[0091] Examples of the bifunctional aromatic compound include 2,2-bis((meth)acryloyloxyphenyl)propane, 2,2-bis[4-(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, 2,2-bis

[0033] Examples of (meth)acrylates include (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.

[0092] 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 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate (UDMA), among others. These include triethylene glycol dimethacrylate (TEGDMA) and 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate, which are excellent in polymerizability and mechanical strength of the resulting zirconia molded body.

[0093] 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 because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded body.

[0094] In both of the above methods (a) and (b), 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, and a duplicated explanation will be omitted here.

[0095] The composition containing the zirconia-based particles and the polymerizable monomer may further contain one or more of the other components, such as the plasticizer, dispersant, emulsifier, antifoaming agent, pH adjuster, and lubricant, as described above.

[0096] When a zirconia molded body is produced by stereolithography using a composition containing zirconia-based particles and a polymerizable monomer, 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.

[0097] When a zirconia molded body is obtained by stereolithography, the content of zirconia-based particles in a composition containing zirconia-based particles and a polymerizable monomer is preferably as high as possible from the viewpoint of subsequent sintering properties. Specifically, the content of zirconia particles in the composition is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. On the other hand, in stereolithography, due to the principle of layered molding, it is preferable that the viscosity of the composition be within a certain range. Therefore, the content of zirconia-based particles in the composition is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less. Adjusting the viscosity of the composition can be particularly important when a controlled liquid level method is carried out in which a zirconia molded body is formed one layer at a time by curing layers by irradiating light from below a container through the bottom surface of the container, in order to raise the cured layer by one layer and allow the composition for forming the next layer to smoothly flow between the underside of the cured layer and the bottom surface of the container.

[0098] The specific viscosity of the composition at 25°C is preferably 20,000 mPa·s or less, more preferably 10,000 mPa·s or less, and even more preferably 5,000 mPa·s or less. Furthermore, the viscosity is preferably 100 mPa·s or more. Since the viscosity of the composition tends to increase as the zirconia particle content increases, it is preferable to appropriately adjust the balance between the zirconia particle content and viscosity of the composition in accordance with the performance of the stereolithography device used, taking into account the balance between the stereolithography speed and the precision of the resulting zirconia molded body. The viscosity can be measured using an E-type viscometer.

[0099] In the method for producing a zirconia molded body of the present invention, the zirconia molded body may be subjected to a humidification treatment followed by a CIP treatment in order to further increase the density of the zirconia molded body. When press molding is performed, a powder containing zirconia particles may be subjected to a humidification treatment before press molding, and then the press molding may be performed. The humidification method may be any known method without any limitation, and may involve spraying water with a spray bottle or using a hygrostat or thermo-hygrostat. The amount of moisture increase due to the humidification treatment depends on the particle size of the zirconia particles contained, the particle size of the stabilizer particles, etc., 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 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 amount of moisture increase due to the humidification treatment can be calculated as a percentage by subtracting the mass of the pre-humidifying powder and the compact from the mass of the moistened powder (powder after the humidification treatment) and the compact, and dividing the result by the mass of the pre-humidifying powder and the compact.

[0100] [Zirconia calcined body] Another embodiment of the present invention is a composition comprising zirconia and a stabilizer capable of suppressing the phase transition of zirconia, wherein at least a portion of the stabilizer is not solid-dissolved in the zirconia, and the monoclinic fraction f is expressed by the following mathematical formula (1): m The calcined zirconia body may have a stabilizing agent content of 50 to 98 mol % and a stabilizer content of 10 to 90 mol % locally. f m =I 28 / (I 28 +I 30 )*100 (1) (In the formula, f m represents the proportion (%) of monoclinic crystals, and in XRD measurements, I 28 represents the area intensity of the peak near 2θ = 28° where the main peak of the monoclinic system appears, and I 30 represents the integrated intensity of the peak near 2θ=30° where the main peak of the tetragonal or cubic crystal system appears.)

[0101] By using this zirconia calcined body, it is possible to obtain a zirconia sintered body that is excellent in translucency and has suppressed opalescence even when sintered for a short period of time.

[0102] The zirconia calcined body can be a precursor (intermediate product) of the zirconia sintered body. In this specification, the zirconia calcined body means a state in which zirconia particles are necked (adhered) to each other and are not completely sintered. The shape of the zirconia calcined body is not particularly limited, and examples thereof include a block shape, a disk shape, and the like. The zirconia calcined body also includes a shaped product. The zirconia calcined body also includes, for example, a precursor before sintering of a dental product (e.g., a crown-shaped prosthesis) obtained by processing a calcined zirconia disk using a CAD / CAM (Computer-Aided Design / Computer-Aided Manufacturing) system.

[0103] In the zirconia calcined body of the present invention, the monoclinic fraction f mmeans the proportion of monoclinic crystals in zirconia calculated by formula (1) relative to the total amount of crystals (monoclinic, tetragonal, and cubic) present in zirconia. Monoclinic fraction f m can be calculated from the above formula (1) based on the peaks in a powder X-ray diffraction (XRD) pattern using CuKα radiation, for example.

[0104] In the zirconia calcined body of the present invention, the monoclinic fraction f m is 50% or more, preferably 55% or more, more preferably 60% or more, and even more preferably 65% ​​or more, based on the total amount of monoclinic, tetragonal, and cubic crystals. m From the viewpoint of easily suppressing opalescence in the sintered body after sintering, the monoclinic fraction f is 98% or less, preferably 94% or less, more preferably 91% or less, and even more preferably 87% or less. Any combination of these ranges may be used. For example, it is preferably 50 to 98%, more preferably 55 to 94%, even more preferably 60 to 91%, and most preferably 65 to 87%. The monoclinic fraction f in the zirconia calcined body m This is thought to contribute to the higher shrinkage temperature and shorter sintering time (excellent translucency even in short sintering times). Monoclinic fraction f in zirconia calcined body m may be adjusted by a building-up process, and the monoclinic fraction f m It can also be adjusted by using a zirconia composition containing a predetermined amount of zirconia particles (powder) having a monoclinic crystal system so as to satisfy the above condition.

[0105] If a peak attributable to the stabilizer is observed in the XRD pattern of the calcined zirconia body, it means that the stabilizer is present in the calcined zirconia body without being solid-dissolved in the zirconia. If the entire amount of the stabilizer is dissolved, generally, no peak attributable to the stabilizer is observed in the XRD pattern. However, depending on conditions such as the crystalline state of the stabilizer, even if no stabilizer peak is present in the XRD pattern, the stabilizer may not be solid-dissolved in the zirconia. If the primary crystal system of zirconia is tetragonal and / or cubic and no stabilizer peak is present in the XRD pattern, it is considered that most, essentially all, of the stabilizer is solid-dissolved in the zirconia. "The primary crystal system is tetragonal and / or cubic" means that the proportion of tetragonal and / or cubic systems is 50% or more of the total amount of crystal systems (monoclinic, tetragonal, and cubic) present in the zirconia. In the zirconia calcined body of the present invention, the stabilizer does not necessarily have to be entirely dissolved in the zirconia. In this specification, the phrase "the stabilizer is solid-dissolved" means that, for example, elements (atoms) contained in the stabilizer are solid-dissolved in zirconia.

[0106] The stabilizer for the zirconia calcined body of the present invention may be the same as the stabilizer for the zirconia composition, and the monoclinic fraction f m Yttria is preferred because it provides a zirconia sintered body with excellent translucency both in normal sintering and in short-term sintering, when combined with the above components. The content of the stabilizer in the zirconia calcined body of the present invention is the same as that of the stabilizer in the zirconia composition, and is, for example, preferably 2 to 9 mol %, more preferably 3 to 8 mol %, based on the total moles of zirconia and the stabilizer.

[0107] Solid solution progresses irreversibly with external energy. Monoclinic fraction f m As the r1 is larger, the r2 is smaller, the yttria content is higher, or the calcination temperature described later is higher, the solid solution progresses, and f m decreases.

[0108] The solid solution is not limited to the thermal energy of calcination, but also progresses in the process of mixing zirconia particles and stabilizer particles, the process of crushing them simultaneously, and / or the process of drying, which will be described later. m decreases.

[0109] In the calcined zirconia body made only from zirconia particles in which the stabilizer is dissolved, the monoclinic fraction f m Therefore, in the zirconia calcined body of the present invention, it is necessary that at least a part of the stabilizer is not solid-dissolved in the zirconia.

[0110] The stabilizer content of the zirconia calcined body of the present invention can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis, etc. In the zirconia calcined body of the present invention, the stabilizer (suitably yttria) content is preferably 2.0 to 9.0 mol %, more preferably 3.0 to 8.0 mol %, based on the total moles of zirconia and stabilizer. If the stabilizer content is less than 2.0 mol%, the translucency of the zirconia sintered body becomes insufficient. If it exceeds 9.0 mol%, the monoclinic fraction f m This is undesirable because it reduces the transmittance due to the crystal structure.

[0111] The zirconia calcined body of the present invention is preferable because the localized dispersion of the stabilizer moderately reduces the regularity of the structure after sintering, resulting in a sintered body with high translucency and low opalescence. In the present invention, "localized" refers to an area equivalent to a circle with a diameter of approximately 10 nm. The presence of both the stabilizer and zirconia within this area is preferable because the crystalline structure after sintering remains small and translucency is improved.

[0112] When the composition of particles derived from a stabilizer in the zirconia calcined body of the present invention is measured locally, elements other than oxygen atoms constituting the stabilizer oxide (e.g., yttrium) are detected inside the stabilizer-derived particles. For example, when the stabilizer contained in the zirconia calcined body of the present invention is yttria, when the composition of particles derived from yttria is measured locally, yttrium is detected inside the yttria-derived particles. Although the yttria-derived particles are mostly composed of yttria, they also contain trace amounts of other elements such as zirconia. When the composition distribution of the zirconia calcined body is observed, the local content (abundance) of elements other than oxygen atoms constituting the stabilizer oxide (e.g., yttrium) in particles derived from a stabilizer (preferably particles derived from yttria) is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more. When the amount of the element is less than 10 mol%, it indicates that the zirconia and stabilizer are almost completely dissolved, resulting in a sintered body containing almost no particles exceeding 100 nm (i.e., a regular crystal structure), resulting in high opalescence, which is undesirable. Furthermore, the local content of elements other than oxygen atoms constituting the oxide of the stabilizer is preferably 90 mol% or less, more preferably 85 mol% or less, and even more preferably 80 mol% or less. When the amount is greater than 90 mol%, it indicates that the zirconia and stabilizer are hardly dissolved, resulting in an increase in areas with little stabilizer outside the stabilizer particles during sintering, which increases the amount of diffusion and lengthens the diffusion distance. This results in an excessive increase in particles exceeding 100 nm in the crystalline structure after sintering, which is undesirable, resulting in reduced translucency ΔL1 and L2. The local content of the element may be within a range determined by any combination of these values. For example, a range of 10 to 90 mol% is preferable, 15 to 85 mol% is more preferable, and 20 to 80 mol% is even more preferable. A content of 10 to 90 mol % is preferable because it allows a zirconia sintered body to have high translucency and low opalescence after sintering.

[0113] The local elemental composition of the zirconia calcined body of the present invention can be confirmed using an electron microscope, such as a transmission electron microscope or a scanning electron microscope. The spatial resolution of the electron microscope can be determined, for example, so that it is smaller than the average primary particle size used in the composition. Examples of such conditions include setting the analysis mode of the electron microscope to point analysis mode and setting the acceleration voltage low (e.g., 100 kV or less, 10 kV or less, etc.). This reduces the range in which the electron beam diffuses within the sample, thereby reducing the area in which characteristic X-rays proportional to the element amount are generated, allowing for more accurate measurements. Another example of such conditions is analyzing the vicinity of the center of gravity of the particle, rather than the particle's periphery, as the analysis point. Another example of such conditions is using an energy-dispersive X-ray analyzer or a wavelength-dispersive X-ray analyzer as the detector. For example, using a wavelength-dispersive detector allows for more accurate measurements.

[0114] The local element composition in the zirconia calcined body of the present invention is affected by the degree of solid solution of the stabilizer in zirconia. For example, the smaller the primary particle size of the stabilizer contained in the composition, the easier it is for the stabilizer to be solid-dissolved in zirconia, and the larger the primary particle size, the more difficult it is for the stabilizer to be solid-dissolved in zirconia. Therefore, the particle size range of the zirconia composition described above is preferable. Furthermore, the solid solution of the stabilizer in zirconia also progresses due to the energy used in the mixing and grinding steps, degreasing, or calcination, and material diffusion progresses, so it is preferable to select an appropriate production method.

[0115] Regarding opalescence, the zirconia calcined body of the present invention has an OP value calculated using the following formula (2) for a 1.2 mm thick sintered body after sintering at 900 to 1400°C for 120 minutes, and from the viewpoint of the appearance of the dental material, the OP value is preferably less than 15, more preferably 10 or less, and even more preferably 7 or less. If the OP value is 15 or more, the body may appear to have a specific color. The opalescence of the 1.2 mm thick sintered body may also mean the value after sintering at 1300°C for 120 minutes. The opalescence refers to the OP value calculated using the following formula (2) after measuring transmitted light and reflected light using a spectrophotometer (manufactured by Konica Minolta Japan, Inc., "CM-3610A") with an F11 light source.

number

[0116] The zirconia calcined body of the present invention preferably has a ΔL*(WB) of 5 or more for a 1.2 mm-thick sintered body after sintering at 900 to 1400°C for 120 minutes, from the viewpoint of sufficient aesthetics as a dental material. If the ΔL*(WB) is less than 5, the white color may be too strong and sufficient transparency may not be obtained. ΔL*(WB) refers to the difference in lightness (L*) between a white background and a black background. Specifically, it refers to the difference between the L* value of a 1.2 mm-thick zirconia sintered body on a white background and the L* value on a black background. The L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013). The white background refers to the white portion of the opacity test paper described in JIS K 5600-4-1:1999, Part 4, Section 1, and the black background refers to the black portion of the opacity test paper. ΔL*(WB) can be measured, for example, using a spectrophotometer (manufactured by Konica Minolta Japan, Inc., "CM-3610A") with an F11 light source.

[0117] In the zirconia calcined body of the present invention, it is preferable that the first translucency ΔL1*(WB) of the first sintered body produced by sintering at 1300°C for 120 minutes and the second translucency ΔL2*(WB) of the second sintered body produced by sintering at 1300°C for 10 minutes satisfy the relationship of the following mathematical formula (3). By being in this range, sufficient aesthetics of the dental material can be maintained even if the sintering time for producing the sintered body is shortened. The first translucency and the second translucency are as described in "Measurement of ΔL*(WB) of zirconia sintered body" in the Examples below. ΔL2*(WB) / ΔL1*(WB)≧0.85 (3)

[0118] The zirconia calcined body of the present invention preferably has a number-based particle size distribution after sintering at 900 to 1400°C for 120 minutes that has at least one peak top in the particle size (crystal grain size) range of 70 to 100 nm, in order to prevent a decrease in translucency ΔL*(WB). A preferred embodiment of the present invention is a zirconia calcined body having two or more peaks in the number-based particle size distribution, in order to reduce the regularity of the crystalline structure after sintering and thereby reduce opalescence. For example, when the number-based particle size distribution after sintering has two peaks, the first peak top (hereinafter also referred to as the "first peak top") is in the particle size (crystal grain size) range of 70 to 100 nm, and the second peak top is in the particle size range exceeding 100 nm. The number-based particle size distribution can be evaluated by the method described in the "Measurement of Crystal Grain Size Distribution in a Zirconia Sintered Body" section of the Examples below. In this specification, the term "crystal grain size" refers to the particle size of a single particle measured by the method described in "Measurement of crystal grain size distribution in a zirconia sintered body" in the Examples below.

[0119] In the zirconia calcined body of the present invention, after sintering at 900 to 1400°C for 120 minutes, the proportion of particles having a particle size exceeding 100 nm in the particle size distribution (by number) of crystal grain size is preferably 3% or more, more preferably 5% or more. By making the proportion 3% or more, the OP value can be reduced. Furthermore, the proportion of particles exceeding 100 nm is preferably 15% or less, more preferably 12% or less. If it is more than 15%, there is a risk of reducing translucency. Any combination of these ranges may be used. For example, the proportion of particles having a particle size exceeding 100 nm is preferably 3 to 15%, more preferably 5 to 12%. The method for measuring the crystal grain size of the sintered body after sintering at 900 to 1400°C is as described in the "Measurement of crystal grain size distribution in zirconia sintered body" section of the Examples below. In a preferred embodiment, the zirconia-based composite material includes any of the above-described structures (for example, zirconia and a stabilizer capable of suppressing the phase transition of zirconia, at least a part of the stabilizer is not solid-dissolved in the zirconia, and the monoclinic fraction f m In addition to the zirconia calcined body in which the amount of the stabilizer is 50 to 98 mol % and the amount of the stabilizer locally present in particles derived from the stabilizer is 10 to 90 mol %, the calcined body may also include a zirconia calcined body in which, after sintering at 900 to 1400°C for 120 minutes, the number-based particle size distribution has at least one peak top in the particle size range of 70 nm to 100 nm and contains 3 to 15% particles with a particle size exceeding 100 nm.

[0120] [Method of manufacturing zirconia calcined body] Another embodiment of the present invention includes a method for producing a zirconia calcined body using the zirconia composition described above. Specifically, the method includes a step of firing (calcining) the zirconia composition described above at 200 to 900°C. The zirconia calcined body can be obtained, for example, by firing (calcining) the zirconia composition described above at 200 to 900°C to remove organic matter, dissolving a desired amount of stabilizer in zirconia, and necking the primary particles.

[0121] The calcination temperature for producing the zirconia calcined body of the present invention is preferably 200°C or higher, more preferably 300°C or higher, and even more preferably 400°C or higher. By setting the temperature at 200°C or higher, organic substances can be removed, and adverse effects in the subsequent sintering process can be easily avoided. Furthermore, the calcination temperature is preferably 900°C or lower, more preferably 700°C or lower, and even more preferably 600°C or lower. By setting the calcination temperature at 900°C or lower, the monoclinic fraction f due to solid solution can be reduced. m This prevents a decrease in transparency and allows excellent translucency to be obtained in a short time in the subsequent sintering step. The calcination temperature may be within any of these combinations. The calcination temperature is, for example, preferably 200 to 900°C, more preferably 300 to 700°C, and even more preferably 400 to 600°C.

[0122] The calcination time for producing the zirconia calcined body of the present invention is preferably 30 minutes or more, more preferably 120 minutes or more. A calcination time of 120 minutes or more is preferable in that it removes organic matter and does not adversely affect the subsequent sintering process. Furthermore, the calcination time is preferably 360 minutes or less, more preferably 240 minutes or less. By setting the calcination time to 240 minutes or less, the monoclinic fraction f due to solid solution can be reduced. m This is preferable because it reduces the decrease in the light transmittance and the diffusion distance of the stabilizer, thereby enabling excellent light transmittance to be obtained in a short time in the subsequent sintering step. The calcination time may be within any combination of these ranges. For example, the calcination time is preferably 30 to 360 minutes, and more preferably 120 to 240 minutes.

[0123] [Zirconia sintered body] Next, the zirconia sintered body of the present invention will be described. The zirconia sintered body of the present invention can be produced using the above-mentioned zirconia composition or zirconia calcined body. Specifically, the zirconia sintered body of the present invention can be obtained, for example, by sintering the above-mentioned zirconia composition or zirconia calcined body. The zirconia sintered body means a zirconia sintered body in a completely sintered state.

[0124] The zirconia sintered body of the present invention contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, and the content of the stabilizer is 2 to 9 mol% relative to the total moles of zirconia and the stabilizer. The stabilizer in the zirconia sintered body of the present invention may be the same as the stabilizer in the zirconia composition, and yttria is preferred from the viewpoint of excellent translucency. A preferred embodiment includes a zirconia sintered body having an yttria content of 2 to 9 mol% relative to the total moles of zirconia and the stabilizer. The content of the stabilizer (preferably yttria) in the zirconia sintered body of the present invention is the same as the stabilizer in the zirconia composition, and is preferably 2 to 9 mol%, more preferably 3 to 8 mol%, relative to the total moles of zirconia and the stabilizer. The yttria content is preferably 2 to 9 mol% from the viewpoint of obtaining sufficient translucency. Furthermore, an yttria content of 9 mol% or less ensures sufficient mechanical strength. Since a zirconia sintered body having excellent translucency and mechanical strength can be obtained, the yttria content in the zirconia sintered body is preferably 3.0 mol% or more, more preferably 4.0 mol% or more, and is preferably 8.0 mol% or less, more preferably 7.0 mol% or less. The yttria content can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis, etc.

[0125] The zirconia sintered body of the present invention has a ΔL*(WB) of 5 or more for a sintered body having a thickness of 1.2 mm. If it is less than 5, the white color is too strong and sufficient transparency cannot be obtained. From the viewpoint of sufficient aesthetics in dental materials, a value of 5 or more is preferable. The method for measuring ΔL*(WB) of the zirconia sintered body is as described in the Examples below.

[0126] The zirconia sintered body of the present invention has an OP value of less than 15 when calculated by the above formula (2) for a sintered body having a thickness of 1.2 mm. If the OP value is 15 or more, the sintered body appears to have a specific color, which is undesirable. From the viewpoint of the appearance of the dental material, the OP value is preferably 10 or less, and more preferably 7 or less. The OP value can be calculated, for example, by measuring transmitted light and reflected light using an F11 light source on a spectrophotometer (manufactured by Konica Minolta Japan, Inc., "CM-3610A") and using the above formula (2).

[0127] Zirconia sintered bodies generally have optical properties such as translucency and opalescence. When the crystal grain size of the zirconia sintered body of the present invention is smaller than the wavelength of visible light, the translucency is improved. Furthermore, due to reduced scattering, the linear light transmittance is also improved. On the other hand, when the crystal grain size is simply smaller than the visible light range, opalescence due to the structure occurs, which appears to be colored and degrades the appearance. The crystal grain size of the sintered body of the present invention refers to the grain size of the crystalline structure inherent in the zirconia sintered body.

[0128] The zirconia sintered body of the present invention preferably has at least one peak top in the particle size distribution on a number basis in the particle size range of 70 nm or more and 100 nm or less, from the viewpoint of not decreasing the translucency ΔL*(WB). In a preferred embodiment, the zirconia sintered body has two or more peak tops in the above range in the number-based particle size distribution, because the peak tops in the above range reduce the regularity of the crystal structure of the sintered body and decrease the opalescence. For example, the zirconia sintered body has two peak tops (bimodal) in the above range. The number-based particle size distribution can be evaluated by the method described in "Measurement of crystal grain size distribution in zirconia sintered body" in the Examples below.

[0129] The average crystal grain size of the zirconia sintered body of the present invention is preferably 100 nm or less from the viewpoint of improving ΔL*(WB). In this specification, the term "average crystal grain size" means the arithmetic mean diameter in the number-based particle size distribution measured by the method described in "Measurement of crystal grain size distribution in zirconia sintered body" in the Examples below. Furthermore, from the viewpoint of suppressing opalescence, in the crystal grain size distribution (particle size distribution on a number basis), the proportion of particles having a particle size (crystal grain size) exceeding 100 nm is preferably 3% or more, more preferably 5% or more. By making this proportion 3% or more, the OP value can be reduced. Furthermore, the proportion of particles having a particle size exceeding 100 nm is preferably 15% or less, more preferably 12% or less. If this proportion is higher than 15%, there is a risk of reducing translucency. Any combination of these ranges may be used. In the crystal grain size distribution of the zirconia sintered body, the proportion of particles having a particle size exceeding 100 nm is, for example, preferably 3 to 15%, more preferably 5 to 12%.

[0130] The zirconia sintered body of the present invention may contain a fluorescent agent. The zirconia sintered body has fluorescence due to the inclusion of a fluorescent agent. There are no particular limitations on the type of fluorescent agent, and one or more fluorescent agents capable of emitting fluorescence with light of any wavelength can be used. Examples of such 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 or more of these metal elements alone. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred, as these elements more significantly exhibit the effects of the present invention. Examples of fluorescent agents used in producing the zirconia sintered body of the present invention 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.

[0131] The content of the fluorescent agent in the zirconia sintered body is not particularly limited and can be adjusted appropriately 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% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, calculated as the oxide of the metal element contained in the fluorescent agent, relative to 100% by mass of zirconia contained in the zirconia sintered body. Furthermore, the fluorescent agent content is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, calculated as the oxide of the metal element contained in the fluorescent agent. When the content is above the lower limit, the fluorescence is comparable to that of natural human teeth. When the content is below the upper limit, the decrease in translucency and mechanical strength can be suppressed.

[0132] The zirconia sintered body of the present invention may contain a colorant. The inclusion of a colorant in the zirconia sintered body results in a colored zirconia sintered body. The type of colorant is not particularly limited, and known pigments commonly used for coloring ceramics, known dental liquid colorants, and the like can be used. Examples of colorants include those containing metal elements, such as oxides containing metal elements such as iron, vanadium, praseodymium, erbium, chromium, nickel, and manganese, composite oxides thereof, and salts thereof. Commercially available colorants can also be used, such as Prettau Color Liquid manufactured by Zirkonzahn. The zirconia sintered body may contain one type of colorant or two or more types of colorants.

[0133] 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, but 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 be 0.1% by mass or less, or even 0.05% by mass or less.

[0134] According to the present invention, a zirconia sintered body having excellent linear light transmittance can be obtained. To adjust the translucency of the zirconia sintered body, the zirconia sintered body of the present invention may contain a translucency adjuster. Specific examples of the translucency adjuster include aluminum oxide, titanium oxide, silicon dioxide, zircon, lithium silicate, and lithium disilicate. The zirconia sintered body may contain one type of translucency adjuster, or may contain two or more types of translucency adjusters.

[0135] 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. However, from the viewpoint of favorable use as a dental prosthesis, the content is preferably 0.1% by mass or less relative to 100% by mass of zirconia contained in the zirconia sintered body.

[0136] [Method of manufacturing zirconia sintered body] The method for producing the zirconia sintered body of the present invention includes a method using the zirconia composition of the present invention (e.g., a molded body). The method for producing the zirconia sintered body is preferably a method including a step of sintering the zirconia composition at 900 to 1400°C under normal pressure. Another embodiment of the present invention is a method for producing a zirconia sintered body using the zirconia calcined body of the present invention, preferably a production method including a step of sintering the zirconia calcined body at 900 to 1400°C under normal pressure. By the above-described production method, the zirconia sintered body of the present invention, which has excellent mechanical strength and translucency and excellent in-line light transmittance, can be easily produced.

[0137] The zirconia sintered body of the present invention can be produced by sintering the zirconia composition of the present invention under normal pressure, and can also be produced by sintering the zirconia calcined body of the present invention under normal pressure.

[0138] In both cases where a sintered body is produced by sintering the zirconia composition (e.g., a molded body) of the present invention, and where a sintered body is produced by sintering the zirconia calcined body of the present invention, the sintering temperature (e.g., the maximum sintering temperature) is preferably set at a temperature that maximizes the translucency and minimizes the opalescence of the zirconia sintered body. From the viewpoint of easily obtaining the desired zirconia sintered body under normal pressure, the sintering temperature is preferably 900°C or higher, more preferably 1000°C or higher, and even more preferably 1050°C or higher, and is preferably 1400°C or lower, more preferably 1350°C or lower, and even more preferably 1300°C or lower. By setting the sintering temperature at or above the lower limit, sintering can be sufficiently carried out, and a dense sintered body can be easily obtained. Furthermore, by setting the sintering temperature at or below the upper limit, a zirconia sintered body having a crystal grain size within the preferred range of the present invention can be easily obtained, and deactivation of the fluorescent agent can be suppressed.

[0139] In both cases where a sintered body is produced by sintering the zirconia composition of the present invention (e.g., a molded body) and where a sintered body is produced by sintering the zirconia calcined body of the present invention, the sintering time is not particularly limited, but in order to be able to efficiently and stably obtain the desired zirconia sintered body with good productivity, the holding time at the sinterable temperature (e.g., the maximum sintering temperature) is preferably less than 120 minutes, more preferably 90 minutes or less, even more preferably 75 minutes or less, even more preferably 60 minutes or less, particularly preferably 45 minutes or less, and most preferably 30 minutes or less. The holding time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more.

[0140] In both cases where a sintered body is produced by sintering the zirconia composition of the present invention (e.g., a molded body) and where a sintered body is produced by sintering the zirconia calcined body of the present invention, the sintering time required to produce the sintered body can be shortened without reducing the translucency and strength of the zirconia sintered body. In particular, the holding time at the maximum sintering temperature required to produce the sintered body can be shortened (short-time sintering). This improves production efficiency, and when the zirconia calcined body of the present invention is used in dental products, it shortens the time required from determining the dimensions of the dental product to be used in treatment and cutting it to making the dental product ready for treatment, thereby reducing the time burden on patients. It also reduces energy costs.

[0141] In the sintering step, the holding time at a sinterable temperature (for example, the maximum sintering temperature) can be, for example, 25 minutes or less, 20 minutes or less, or 15 minutes or less.

[0142] The temperature increase and decrease rates in the sintering step are preferably set so as to shorten the time required for the sintering 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 sintering 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, or 200°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.

[0143] The sintering in the present invention can be carried out using a sintering furnace. There are no particular limitations on the type of sintering furnace, and for example, electric furnaces and degreasing furnaces used in general industry can be used. In particular, when used for dental materials, in addition to conventional sintering furnaces for dental zirconia, dental porcelain furnaces with relatively low sintering temperatures (for example, maximum sintering temperatures) can also be used.

[0144] The zirconia sintered body of the present invention has both high translucency and low opalescence. Moreover, since the zirconia sintered body of the present invention has excellent translucency even when sintered for a short time, it is preferable that the first translucency ΔL1*(WB) of the first sintered body produced by sintering at 1300°C for 120 minutes and the second translucency ΔL2*(WB) of the second sintered body produced by sintering at 1300°C for 10 minutes satisfy the relationship of the following mathematical formula (3). The first translucency and the second translucency are as described in "Measurement of ΔL*(WB) of zirconia sintered body" in the Examples described later. ΔL2*(WB) / ΔL1*(WB)≧0.85 (3)

[0145] The zirconia sintered body of the present invention can be easily produced without HIP treatment, but by performing HIP treatment after the above-mentioned sintering under normal pressure, it is possible to further improve the translucency and mechanical strength.

[0146] [Uses of zirconia sintered body] There are no particular limitations on the uses of the zirconia sintered body of the present invention. The zirconia sintered body has excellent translucency and excellent in-line light transmittance, and is therefore particularly suitable as a dental material for dental prostheses, etc. In particular, it is extremely useful not only as a dental prosthesis used in the cervical region of teeth, but also as a dental prosthesis used on the occlusal surfaces of molars and the incisal edges of front teeth. The zirconia sintered body of the present invention is preferably used as a dental prosthesis used in the incisal edges of front teeth. [Example]

[0147] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples, etc. The respective measurement methods are as follows.

[0148] <Method for measuring average primary particle size of zirconia and stabilizer in zirconia composition> The zirconia particles and / or stabilizer particles were photographed using a transmission electron microscope (TEM), and the circle-equivalent diameter (the diameter of a perfect circle with the same area) of any 100 particles on the obtained image was calculated from the area of ​​each particle using the following formula, and the average circle-equivalent diameter of the 100 particles was taken as the average primary particle diameter. R=2(S / π) (1 / 2) (In the formula, S represents the particle area, and R represents the particle size (diameter).)

[0149] <Content of stabilizer in zirconia composition (mol%)> The stabilizer content (mol %) in the zirconia composition was measured as the stabilizer content relative to the total moles of zirconia and stabilizer using an X-ray fluorescence analyzer (XRF) (RX3000, manufactured by Matsusada Precision Co., Ltd.).

[0150] <Method for measuring half-width of peak derived from stabilizer in zirconia composition> The half-width of the peak derived from the stabilizer in the zirconia composition of the present invention was measured using a powder obtained by drying the zirconia composition at room temperature as a sample, using a fully automated horizontal multipurpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and integrated X-ray analysis software (SmartLab Studio II, manufactured by Rigaku Corporation) under the following conditions, and the half-width of the peak at around 29° was determined. X-ray source: Cu Kα (λ=1.54186Å) Goniometer length: 300 mm Optical system: Concentration method Detector: High-speed one-dimensional X-ray detector (D / teX Ultra250) Monochromatization: Kβ filter Tube voltage: 40kV Tube current: 30mA Scan axis: 2θ / θ Scan speed: 0.2° / min Sampling step: 0.01°

[0151] <Monoclinic fraction of calcined zirconia body f m Measurement of The monoclinic crystal ratio f of the present invention m was determined by analyzing the crystalline phase of the calcined body. Specifically, X-ray diffraction (XRD) measurements were performed and the value was calculated from the following formula: f m =I 28 / (I 28 +I 30 )*100 (1) (In the formula, f m represents the proportion (%) of monoclinic crystals, and in XRD measurements, I 28 represents the area intensity of the peak near 2θ = 28° where the main peak of the monoclinic system appears, and I 30 represents the integrated intensity of the peak near 2θ=30° where the main peak of the tetragonal or cubic crystal system appears.) For the measurement, disk-shaped zirconia calcined bodies of each of the examples and comparative examples were used as samples.

[0152] <Method for measuring composition distribution of zirconia calcined body> The composition distribution of the zirconia calcined body was measured using a field-emission scanning electron microscope (FE-SEM Reglus8220, Hitachi High-Tech Corporation) and an energy-dispersive X-ray analyzer (Aztec Energy X-Max50, Oxford Instruments) under the following conditions. Zirconia was observed at 2.042 keV and yttrium at 1.923 keV. The average yttrium content (mol%) of 10 stabilizer particles was calculated. Measurement magnification: 20,000 times Analysis Mode: Point Analysis Accelerating voltage: 5 kV Working distance: 15mm±1mm X-ray extraction angle: 30 degrees Dead time: 7% Measurement time: 100 seconds

[0153] <Measurement of ΔL*(WB) of zirconia sintered body> The ΔL*(WB) of the zirconia sintered body was measured using a spectrophotometer (Konica Minolta Japan, Inc., "CM-3610A"). ΔL*(WB) refers to the difference between the lightness (L*) on a white background and the lightness (L*) on a black background. The L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013). The white background refers to the white portion of the opacity test paper described in Section 1 of Part 4 of JIS K 5600-4-1:1999, and the black background refers to the black portion of the opacity test paper. The measurement was performed using an F11 light source and measuring reflected light. A disk-shaped zirconia sintered body with a diameter of 16 mm and a thickness of 1.2 mm, obtained by mirror polishing, was used as the sample. For the zirconia sintered body of the sample, both a zirconia sintered body (first sintered body) obtained by holding for 120 minutes at the maximum sintering temperature of 1300°C (120-minute sintering) and a zirconia sintered body (second sintered body) obtained by holding for 10 minutes at the maximum sintering temperature of 1300°C (10-minute sintering) were produced, and the average values ​​measured for each with n=3 were calculated. The first translucency ΔL1*(WB) of the first sintered body produced by sintering at 1300°C for 120 minutes and the second translucency ΔL2*(WB) of the second sintered body produced by sintering at 1300°C for 10 minutes were determined, and the relationship between the first translucency ΔL1*(WB) and the second translucency ΔL2*(WB) was also evaluated. For Comparative Examples 1, 2, 5 and 6, except that the maximum sintering temperature was changed as shown in Table 2, ΔL*(WB) was measured as translucency in the same manner as above.

[0154] <Opal properties of zirconia sintered body> To evaluate the opalescence of the zirconia sintered body, the disk-shaped zirconia sintered body having a diameter of 16 mm and a thickness of 1.2 mm used in the measurement of ΔL*(WB) above was used as a sample. The opalescence of the zirconia sintered body was determined by measuring transmitted light and reflected light using a spectrophotometer (manufactured by Konica Minolta Japan, Inc., "CM-3610A") with an F11 light source, and calculating the OP value using the following formula (2).

number

[0155] <Measurement of crystal grain size in zirconia sintered body and calculation of particle size distribution> The surfaces of the zirconia sintered bodies obtained in the following examples or comparative examples were imaged using a scanning electron microscope (product name "VE-9800", manufactured by Keyence Corporation). The grain boundaries of each crystal grain were then depicted in the resulting images, and the crystal grain size of each crystal grain was measured by image analysis. Image analysis software (product name "Image-Pro Plus", manufactured by Hakuto Co., Ltd.) was used to measure the crystal grain size. The captured SEM images were binarized, and the brightness range was adjusted to clearly show the grain boundaries. The particles were then recognized from the field of view (area). The crystal grain size obtained using Image-Pro Plus is the diameter passing through the center of gravity of the particle. The crystal grain size is calculated by measuring the length of the line segment connecting the outlines of the particles passing through the center of gravity at two-degree intervals around the center of gravity and averaging the length. In the SEM photographs (10 fields of view) of each example and comparative example, the crystal grain size was measured for all crystal grains that did not overlap the image edges. The relationship between the crystal grain size and the number of crystals for each particle obtained was graphed to create a particle size distribution (particle size distribution based on number). In addition, by graphing the relationship between the size (area) of the crystals obtained from each crystal particle and the number of crystals, a crystal chart (area distribution based on number) such as that shown in Figure 5 can also be created. "Particles not on the image edge" refers to particles excluding particles whose outlines do not fit completely within the screen of the SEM photograph (particles whose outlines end at the top, bottom, left, and right boundary lines). The crystal grain size of all particles not on the image edge was determined by selecting the option to exclude all particles on boundary lines in Image-Pro Plus.

[0156] <Measurement of in-line light transmittance> The linear light transmittance of the zirconia sintered body at a thickness of 1.0 mm was measured using a turbidity meter (Nippon Denshoku Industries Co., Ltd., "Haze Meter NDH 4000"), with light emitted from a light source being transmitted through and scattered by the sample, and an integrating sphere. In this measurement, linear light transmittance was measured in accordance with ISO 13468-1:1996 and JIS K 7361-1:1997, and haze was measured in accordance with ISO 14782-1:1999 and JIS K 7136:2000, and linear light transmittance was measured. For the measurement, a disk-shaped zirconia sintered body with a diameter of 16 mm and a thickness of 1.0 mm and mirror-polished on both sides was used as the sample.

[0157] [Production Example 1] (Zirconia particles with an average primary particle diameter r1 of 35 nm) 1.0 L of a 0.62 mol / L aqueous zirconium oxychloride solution and 0.5 L of a 1.9 mol / L aqueous sodium hydroxide solution were prepared. 1.0 L of pure water was poured into the precipitation tank, and then the aqueous zirconium oxychloride solution and the aqueous sodium hydroxide solution were simultaneously poured thereinto to precipitate zirconium oxychloride, thereby obtaining a slurry. After filtering and washing, 22.2 g of acetic acid was added to the slurry, which was then hydrothermally treated at 200°C for 2 hours. The resulting slurry was centrifuged through a membrane filter with a pore size of 100 nm to remove coarse particles, yielding a zirconia slurry. The average primary particle size of the zirconia particles was 35 nm. The resulting slurry was concentrated using an evaporator to obtain a water slurry containing 20 mass% of zirconia particles.

[0158] [Production Example 2] (Zirconia particles with an average primary particle diameter r1 of 50 nm) The slurry of Production Example 1 was placed in a centrifuge tube and processed at 3000 rpm for 5 minutes, and the upper half of the slurry in the centrifuge tube was removed to obtain a zirconia slurry. The average primary particle diameter of the zirconia particles contained in this zirconia slurry was 50 nm. This was concentrated using an evaporator to obtain a water slurry containing 20 mass% of zirconia particles.

[0159] [Production Example 3] (Zirconia particles with an average primary particle diameter r1 of 10 nm) The slurry of Production Example 1 was placed in a centrifuge tube and processed at 3,000 rpm for 5 minutes, and the supernatant was removed by decantation to obtain a zirconia slurry. The average primary particle diameter of the zirconia particles contained in this zirconia slurry was 10 nm. This was concentrated using an evaporator to obtain a water slurry containing 20 mass% of zirconia particles.

[0160] [Production Example 4] (Yttria particles with an average primary particle diameter r2 of 20 nm) 3 kg of yttrium oxide was added to 7 kg of water and crushed in a bead mill to obtain a water slurry in which yttrium oxide was dispersed. The obtained slurry was centrifuged using a membrane filter with a pore size of 100 nm to remove coarse particles, obtaining a yttria slurry. The average primary particle diameter of the yttria particles contained in this slurry was 20 nm. This was concentrated using an evaporator to obtain a water slurry containing 20 mass% yttria particles.

[0161] [Production Example 5] (Yttria particles with an average primary particle diameter r2 of 50 nm) The slurry of Production Example 4 was placed in a centrifuge tube and processed at 3000 rpm for 5 minutes. The upper half of the slurry in the centrifuge tube was removed to obtain a yttria slurry. The average primary particle diameter of the yttria particles contained in this yttria slurry was 50 nm. This was concentrated using an evaporator to obtain a water slurry containing 20 mass% of yttria particles.

[0162] [Production Example 6] (Yttria particles with an average primary particle diameter r2 of 10 nm) The slurry of Production Example 4 was placed in a centrifuge tube and processed at 3000 rpm for 5 minutes, and the supernatant was removed by decantation to obtain an yttria slurry. The average primary particle diameter of the yttria particles contained in this yttria slurry was 10 nm. This was concentrated using an evaporator to obtain a water slurry containing 20 mass% of yttria particles.

[0163] [Production Example 7] (Zirconia particles with an average primary particle diameter r1 of 100 nm) 3 kg of zirconia was added to 7 kg of water and crushed in a bead mill to obtain a water slurry containing dispersed zirconia. The average primary particle diameter of the zirconia particles contained in this slurry was 100 nm. This was concentrated in an evaporator to obtain a water slurry containing 20 mass% of zirconia particles.

[0164] [Production Example 8] (Yttria particles with an average primary particle diameter r2 of 100 nm) 3 kg of yttria was added to 7 kg of water and crushed in a bead mill to obtain a water slurry containing dispersed yttrium oxide. The average primary particle diameter of the yttria particles contained in this slurry was 100 nm. This was concentrated in an evaporator to obtain a water slurry containing 20 mass% of yttria particles.

[0165] [Production Example 9] (Particles in which yttria is solid-dissolved in zirconia, with an average primary particle diameter of 40 nm) 1.0 L of a mixed aqueous solution containing 0.62 mol / L of zirconium oxychloride and 0.052 mol / L of yttrium chloride, and 0.5 L of a 1.9 mol / L aqueous sodium hydroxide solution were prepared. 1.0 L of pure water was poured into a precipitation tank, and then the mixed aqueous solution and the aqueous sodium hydroxide solution were simultaneously poured thereinto to co-precipitate zirconium oxychloride and yttrium chloride, thereby obtaining a slurry. After filtering and washing, 22.2 g of acetic acid was added to the slurry, which was then hydrothermally treated at 220°C for 3 hours. The resulting slurry was centrifuged through a membrane filter with a pore size of 100 nm to remove coarse particles, yielding a zirconia slurry. The average primary particle size of the yttria-dissolved zirconia particles contained in this slurry was 40 nm. The slurry was concentrated using an evaporator to obtain a water slurry containing 20 mass% yttria-dissolved zirconia particles.

[0166] [Production Example 10] (Particles in which yttria is solid-dissolved in zirconia, with an average primary particle diameter of 15 nm) 1.0 L of a mixed aqueous solution containing 0.62 mol / L of zirconium oxychloride and 0.065 mol / L of yttrium chloride, and 0.5 L of a 1.9 mol / L aqueous sodium hydroxide solution were prepared. 1.0 L of pure water was poured into a precipitation tank, and then the mixed aqueous solution and the aqueous sodium hydroxide solution were simultaneously poured thereinto to co-precipitate zirconium oxychloride and yttrium chloride, thereby obtaining a slurry. After filtering and washing, 22.2 g of acetic acid was added to the slurry, which was then hydrothermally treated at 190°C for 2 hours. The resulting slurry was centrifuged through a membrane filter with a pore size of 100 nm, and purified water was added to a solids concentration (zirconia and yttria concentration) of 5.0 mass% to obtain a zirconia slurry from which coarse particles had been removed. The average primary particle diameter of the zirconia particles contained in this zirconia slurry was 15 nm.

[0167] [Example 1] The slurries obtained in Production Examples 3 and 5 were used at 94.6% by mass and 5.4% by mass, respectively, and isopropanol was added in an amount 9 times the volume of the slurry. The mixture was placed in a centrifuge tube, thoroughly mixed, and centrifuged at 4000 rpm for 10 minutes. After confirming the precipitation of white matter, the supernatant was removed. Isopropanol was added again, thoroughly mixed, and centrifuged at 4000 rpm for 10 minutes. After confirming the precipitation of white matter, the supernatant was removed. Methanol was added to the mixture to make the volume the same as the slurry used, and further mixed thoroughly to obtain a methanol-substituted slurry. The residual water content of this methanol-substituted slurry was measured using a Karl Fischer moisture meter and was found to be 0.08% by mass. To the obtained slurry, 1% by mass of glycerin was added relative to 100% by mass of the solid content (zirconia and yttria) of the slurry, and 2% by mass of the acrylic binder "KFE-124" (manufactured by GOO Chemical Industry Co., Ltd.) relative to 100% by mass of the solid content was added, and the mixture was subjected to ultrasonic dispersion at 40 kHz for 1 hour to obtain an additive-containing slurry. The resulting additive-containing slurry was supercritically dried using a supercritical drying apparatus according to the following procedure. Specifically, the additive-containing slurry was first placed in a pressure vessel, which was then connected to a supercritical carbon dioxide extraction apparatus. The absence of pressure leaks was confirmed. The pressure vessel and preheating tube were then immersed in a water bath heated to 60°C, the temperature was raised to 80°C, and the pressure was increased to 25 MPa. The mixture was then allowed to stand for 10 minutes for stabilization. Next, carbon dioxide and methanol as an entrainer were introduced under specified conditions (temperature: 80°C, pressure: 25 MPa, carbon dioxide flow rate: 10 mL / min, entrainer (methanol) flow rate: 1.5 mL / min). After 2 hours, the introduction of methanol was stopped, and the introduction of carbon dioxide alone was continued. After 2 hours of carbon dioxide introduction alone, the carbon dioxide flow was stopped, and the pressure was gradually reduced from 25 MPa over approximately 20 minutes to normal pressure while maintaining the temperature at 80°C. The pressure vessel was removed from the water bath and cooled to room temperature. The vessel was then opened and the treated sample was recovered to obtain a zirconia composition containing zirconia particles and yttria particles. The yttria content in the zirconia composition was measured using an X-ray fluorescence analyzer (XRF analyzer) and found to be 3 mol%. The particle size distribution of the obtained zirconia composition is shown in Figure 1. The XRD pattern of yttria in the obtained zirconia composition is shown in Figure 2.

[0168] The obtained powder was molded into disks of a predetermined size using a uniaxial press, and these were subjected to cold isostatic pressing (CIP) (pressure 200 MPa) to increase the density and obtain zirconia molded bodies. The size of the zirconia molded body was set to 20 mm in diameter so that it could be processed to the size of the zirconia sintered body described in the evaluation of each property described above, taking into account shrinkage due to sintering and reduction in thickness due to polishing, and multiple zirconia molded bodies of different thicknesses were manufactured.

[0169] This zirconia compact was calcined at 500°C for 2 hours under normal pressure to obtain a calcined zirconia body. Fig. 3 shows the composition distribution (SEM-EDX) of the crystalline structure of the calcined zirconia body obtained.

[0170] This zirconia calcined body was sintered at 1300°C for 2 hours under normal pressure to obtain a zirconia sintered body.

[0171] [Example 2] A zirconia composition, a calcined body, and a sintered body were obtained in the same manner as in Example 1, except that the slurries obtained in Production Examples 2 and 6 were used in amounts of 94.6 mass% and 5.4 mass%, respectively. The yttria content in the composition was measured with an XRF device and was found to be 3 mol%.

[0172] [Example 3] A zirconia composition, a calcined body, and a sintered body were obtained in the same manner as in Example 1, except that the slurries obtained in Production Examples 1 and 4 were used in amounts of 92.1 mass% and 7.9 mass%, respectively. The yttria content in the composition was measured with an XRF device and was found to be 4.5 mol%.

[0173] [Example 4] A zirconia composition, a calcined body, and a sintered body were obtained in the same manner as in Example 1, except that the slurries obtained in Production Examples 3 and 5 were used in amounts of 86.3 mass% and 13.7 mass%, respectively. The yttria content in the composition was measured with an XRF device and was found to be 8 mol%.

[0174] [Example 5] A zirconia composition, a calcined body, and a sintered body were obtained in the same manner as in Example 1, except that the slurries obtained in Production Examples 2 and 6 were used in amounts of 86.3 mass% and 13.7 mass%, respectively. The yttria content in the composition was measured with an XRF device and was found to be 8 mol%.

[0175] [Comparative Example 1] Using the slurry obtained in Production Example 9, a zirconia molded body and a calcined body were obtained in the same manner as in Example 1. The content of yttria in the slurry was measured with an XRF device and was found to be 4 mol %. This calcined body was placed in a sialon container, set for HIP treatment, and treated in argon gas at a temperature of 1100°C and a pressure of 150 MPa, then cooled to room temperature. The treated product was then heat treated in air at normal pressure at a temperature of 1000°C to obtain a zirconia sintered body.

[0176] Comparative Example 2 Using the slurry obtained in Production Example 10, a zirconia molded body and a calcined body were obtained in the same manner as in Example 1. A diagram showing the composition distribution (SEM-EDX) of the crystalline structure of the obtained calcined zirconia body is shown in Figure 4. The yttria content in the slurry was measured with an XRF device and was found to be 5 mol%. This zirconia calcined body was sintered at 1100°C for 2 hours under normal pressure to obtain a zirconia sintered body.

[0177] Comparative Example 3 A zirconia composition, a calcined body, and a sintered body were obtained in the same manner as in Example 1, except that the slurries obtained in Production Examples 7 and 6 were used in amounts of 91.2 mass% and 8.8 mass%, respectively. The yttria content in the composition was measured with an XRF device and was found to be 5 mol%.

[0178] Comparative Example 4 A zirconia composition, a calcined body, and a sintered body were obtained in the same manner as in Example 1, except that the slurries obtained in Production Examples 3 and 8 were used in amounts of 91.2 mass% and 8.8 mass%, respectively. The yttria content in the composition was measured with an XRF device and was found to be 5 mol%.

[0179] Comparative Example 5 Comparative Example 5 was carried out in the following manner, corresponding to Example 1 of Patent Document 3 (WO 2020 / 179877). 1.0 L of a 0.62 mol / L aqueous zirconium oxychloride solution, 1.0 L of a 0.038 mol / L aqueous yttrium chloride solution, and two 0.5 L solutions of a 1.9 mol / L aqueous sodium hydroxide solution were prepared. Two precipitation tanks were prepared, and 1.0 L of pure water was poured into each precipitation tank. An aqueous zirconium oxychloride solution and an aqueous sodium hydroxide solution were simultaneously poured into one of the tanks, and an aqueous yttrium chloride solution and an aqueous sodium hydroxide solution were simultaneously poured into the other tank, thereby precipitating zirconium oxychloride and yttrium chloride, respectively, to obtain slurries. After filtering and washing, 22.2 g of acetic acid was added to each slurry and hydrothermally treated at 200°C for 3 hours. The resulting slurries were centrifuged through a membrane filter with a 100 nm pore size, and purified water was added to a solids concentration (zirconia and yttria concentrations, respectively) of 5.0 mass% to produce zirconia and yttria slurries from which coarse particles had been removed. The average primary particle diameter of the zirconia and yttria particles contained in each slurry was 15 nm, and no particles with a particle diameter exceeding 100 nm were observed. 0.5 L of the yttria slurry was gradually added dropwise to 0.5 L of the zirconia slurry at a rate of 10 mL / min at room temperature to obtain 1 L of mixed slurry. The yttria content in the slurries was measured using an XRF device and was found to be 3 mol%. The mixed slurry was poured into a plaster mold as a molding slurry, left at room temperature for 2 weeks, and then subjected to cold isostatic pressing (CIP) (pressure 170 MPa) to increase the density and obtain a zirconia molded body. The plaster mold was made so that the shape of the molded body before CIP would be a disk with a diameter of 20 mm and a thickness of 2.5 mm. The plaster mold was prepared by mixing plaster (Noritake Dental Plaster, manufactured by Kuraray Noritake Dental Co., Ltd.) with water at a mixing ratio of 50 mass %. This zirconia molded body was calcined at 500°C under normal pressure for 2 hours to obtain a calcined zirconia body. Furthermore, this zirconia calcined body was sintered at 1100°C for 10 minutes under normal pressure to obtain a zirconia sintered body containing 3 mol% of yttria.

[0180] Comparative Example 6 Comparative Example 6, which corresponds to Example 11 of Patent Document 3 (WO 2020 / 179877), was carried out by the following method. 1.0 L of a mixed aqueous solution containing 0.62 mol / L of zirconium oxychloride and 0.066 mol / L of yttrium chloride, and 0.5 L of a 1.9 mol / L aqueous sodium hydroxide solution were prepared. 1.0 L of pure water was poured into a precipitation tank, and then the mixed aqueous solution and the aqueous sodium hydroxide solution were simultaneously poured thereinto to co-precipitate zirconium oxychloride and yttrium chloride, thereby obtaining a slurry. After filtering and washing, 22.2 g of acetic acid was added to the slurry and hydrothermally treated at 200°C for 1 hour. The resulting slurry was centrifuged through a membrane filter with a 100 nm pore size, and purified water was added to a solids concentration (zirconia and yttria concentration) of 5.0 mass% to produce a zirconia slurry from which coarse particles had been removed. The zirconia slurry contained 0.28 mass% of zirconia particles with a particle size greater than 100 nm. The yttria content in the slurry was measured using an XRF device and found to be 5 mol%. A zirconia compact, a zirconia calcined body, and a zirconia sintered body each containing 5 mol % of yttria were obtained in the same manner as in Comparative Example 5, except that the zirconia slurry obtained above was used as a molding slurry.

[0181] The results of measurements performed by the above-mentioned methods for each of the Examples and Comparative Examples are shown in Tables 1 and 2.

[0182] [Table 1]

[0183] [Table 2]

[0184] As shown in Table 2, it was confirmed that in Examples 1 to 5, the occurrence of structural color could be suppressed, opalescence could be reduced, and excellent translucency was achieved even with short-time sintering. In Examples 1 to 5, at least a portion of the yttria was not dissolved in zirconia, and the composition distribution of the crystal structure of the calcined zirconia body had a predetermined local content (abundance) of the yttrium element, resulting in a partially irregular crystal structure as shown in Figure 3 (Example 1), and the sintered body after sintering contained a predetermined amount of particles exceeding 100 nm, which is thought to be why the opalescence was reduced. On the other hand, in Comparative Examples 1 to 3 and 5 to 6, the opalescence could not be reduced. In Comparative Examples 1 and 2, zirconium and yttrium were in solid solution, and the amount of yttrium present in the composition distribution was small. Therefore, as shown in Figure 4 (Comparative Example 2), the sintered body had a regular crystal structure after sintering, and there were almost no particles exceeding 100 nm in the sintered body, which is thought to be why the opalescence could not be reduced. In Comparative Example 3, the monoclinic ratio f m It is thought that the opalescence could not be reduced because the temperature was low. In Comparative Example 4, the average particle size of the yttria particles in the zirconia composition was too large, and the translucency was not excellent even with normal sintering. Furthermore, as shown in Comparative Example 5, when yttria is produced in a liquid phase, unlike the Examples, the zirconia composition has low crystallinity, and the half width of the peak derived from the stabilizer in the XRD pattern cannot be set within the desired range of the present invention. m It was also not possible to achieve the desired range of the present invention. Furthermore, as shown in Comparative Example 6, even if the average particle size (r1) of the zirconia particles and the average particle size (r2) of the stabilizer particles used in the zirconia composition were within the desired ranges, the crystallinity of the zirconia composition was low, and the half-width of the peak derived from the stabilizer in the XRD pattern did not fall within the desired range of the present invention. m Even if the amount of the stabilizer present locally could be adjusted to the desired range of the present invention, the amount of the stabilizer present locally could not be adjusted to the desired range of the present invention.

[0185] Furthermore, for the zirconia sintered bodies according to Comparative Example 2 and Example 1, a crystal chart (area distribution based on number) is shown in FIG. 5, which is a graph showing the relationship between the size (area) of the crystals obtained from each crystal particle and the number of crystals. As can be seen from the comparison between Comparative Example 2 (left side) and Example 1 (right side) in FIG. 5, Example 1 contains a relatively large number of particles with a large particle size. In Example 1, in the particle size distribution based on number, the proportion of particles having a particle size exceeding 100 nm (corresponding to the "next class" in FIG. 5) was within the range of 3% to 15%.

Claims

1. The composition contains zirconia particles and stabilizer particles capable of suppressing the phase transition of zirconia, The average particle size (r1) of the zirconia particles is 1 to 60 nm, and the average particle size (r2) of the stabilizer particles is 1 to 60 nm, The zirconia composition has a peak attributable to the stabilizer in a powder X-ray diffraction pattern using CuKα radiation, the peak having a half-value width of 0.05° to 1.0°.

2. 2. The zirconia composition according to claim 1, wherein the content of the stabilizer is 2 to 9 mol % based on the total moles of the zirconia and the stabilizer.

3. 3. The zirconia composition of claim 1, wherein the stabilizer is yttria.

4. 3. The zirconia composition of claim 1, wherein the zirconia particles comprise a monoclinic crystal.

5. The composition contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, At least a part of the stabilizer is not solid-dissolved in zirconia, and satisfies the following formula (1): f m = I 28 / (I 28 + I 30 ) * 100 (1) (wherein f m represents the proportion (%) of the monoclinic system, and in the XRD measurement, I 28 represents the integrated intensity of the peak near 2θ=28° where the main peak of the monoclinic system appears, and I 30 represents the integrated intensity of the peak near 2θ=30° where the main peak of the tetragonal or cubic system appears.) The monoclinic ratio f m is 50 to 98%, and the local abundance of the stabilizer in the particles derived from the stabilizer is 10 to 90 mol %; The locally existing amount of the stabilizer means the amount of elements other than oxygen atoms constituting the oxide of the stabilizer present inside the particles derived from the stabilizer, and is measured under the following conditions using a field emission scanning electron microscope (FE-SEM Reglus 8220, manufactured by Hitachi High-Tech Corporation) and an energy dispersive X-ray analyzer (Aztec Energy X-Max 50, manufactured by Oxford Instruments), and is the average value of the measurement results for 10 particles derived from the stabilizer: Zirconia calcined body. Measurement magnification: 20,000 times Analysis mode: Point analysis Acceleration voltage: 5 kV Working distance: 15mm ±1mm X-ray extraction angle: 30 degrees Dead time: 7% Measurement time: 100 seconds

6. 6. The zirconia calcined body according to claim 5, wherein the content of the stabilizer is 2 to 9 mol% based on the total moles of the zirconia and the stabilizer.

7. 7. The zirconia calcined body according to claim 5, wherein the stabilizer is yttria.

8. 7. The zirconia calcined body according to claim 5 or 6, wherein the OP value calculated using the following formula (2) in a sintered body having a thickness of 1.2 mm after sintering at 900 to 1400 ° C. for 120 minutes is less than 15. [Equation 1] (In the formula, a * 透過 and b * 透過 represents the color coordinates of the L*a*b* color system in transmitted light, and a * 反射 and b * 反射 represents the color coordinates of the L*a*b* color system in reflected light.)

9. 7. The zirconia calcined body according to claim 5, wherein the sintered body after sintering at 900 to 1400°C for 120 minutes has a number-based particle size distribution that has at least one peak top in a particle size range of 70 nm to 100 nm, and contains 3 to 15% particles having a particle size exceeding 100 nm.

10. The zirconia calcined body according to claim 5 or 6, wherein a sintered body having a thickness of 1.2 mm after sintering at 900 to 1400 ° C. for 120 minutes has a ΔL * (W - B) of 5 or more.

11. First light transmittance ΔL of the first sintered body produced by sintering at 1300° C. for 120 minutes 1 *(W-B) and the second light transmittance ΔL of the second sintered body produced by sintering at 1300° C. for 10 minutes 2 *(W−B) satisfies the relationship of the following mathematical formula (3): The zirconia calcined body according to claim 5 or 6. ΔL 2 *(W-B) / ΔL 1 *(W-B)≧0.85 (3)

12. A method for producing a zirconia calcined body, comprising a step of calcining the zirconia composition according to claim 1 or 2 at 200 to 900°C.

13. Contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, The content of the stabilizer is 2 to 9 mol% with respect to the total moles of zirconia and the stabilizer, and ΔL * (W-B) in a sintered body having a thickness of 1.2 mm is 5 or more, and the OP value calculated using the following formula (2) is 7 or less. A zirconia sintered body. [Equation 2] (In the formula, a * 透過 and b * 透過 represents the color coordinates of the L*a*b* color system in transmitted light, and a * 反射 and b * 反射 represents the color coordinates of the L*a*b* color system in reflected light.)

14. 14. The zirconia sintered body according to claim 13, wherein the stabilizer is yttria.

15. The zirconia sintered body according to claim 13 or 14, wherein the number-based particle size distribution has at least one peak top in the particle diameter range of 70 nm or more and 100 nm or less, and contains 3 to 15% particles having a particle diameter exceeding 100 nm.

16. A method for producing a zirconia sintered body, comprising a step of sintering the zirconia composition according to claim 1 or 2, or the zirconia calcined body according to claim 5 or 6, at 900 to 1400°C.

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