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

Abstract

This invention provides a zirconia composition with excellent light transmittance and suppression of opalescence in sintered bodies, a zirconia pre-sintered body using the composition, a zirconia sintered body, and a method for easily manufacturing them. The invention relates to a zirconia composition comprising zirconia particles and stabilizer particles capable of suppressing the phase transformation of zirconia, wherein the average particle size (r1) of the zirconia is 1–60 nm, and the average particle size (r2) of the stabilizer is 1–60 nm, and the full width at half maximum (FWHM) of the peaks originating from the stabilizer in a CuKα-ray-based powder X-ray diffraction pattern is 0.05°–1.0°. By using this zirconia composition, the structural regularity of the zirconia sintered body can be reduced, wavelength-selective reflection and / or transmission can be suppressed, and opalescence can be suppressed, thus obtaining a zirconia sintered body with excellent light transmittance and low opalescence.

Description

Technical Field

[0001] The present invention relates to sintered zirconium oxide (zirconia (IV); ZrO2) bodies that have both high light transmittance and low opalescence, pre-sintered bodies for obtaining sintered bodies, and compositions thereof, as well as methods for manufacturing the same. Background Technology

[0002] In recent years, from an aesthetic point of view, sintered zirconia containing yttrium oxide has been used in dental materials such as dental fillings, replacing traditional metal dental fillings such as silver teeth. These dental fillings are mostly manufactured by forming zirconia granules or slurries containing the granules into zirconia shaped bodies with desired shapes such as discs or prisms, pre-firing them to form pre-fired bodies (millblanks), milling them into the desired shape of the dental filling, and then sintering them to complete the manufacturing process.

[0003] To date, it has been confirmed that reducing the grain size and uniformity of zirconia sintered bodies improves linear light transmittance (see, for example, Patent Document 1). Hot isostatic pressing (HIP) is required to reduce and homogenize the grain size of zirconia sintered bodies. However, since the HIP apparatus used in HIP processing is a special device classified as a high-pressure gas manufacturing equipment, it is difficult to easily obtain zirconia sintered bodies with high linear light transmittance.

[0004] Therefore, a zirconia sintered body with excellent mechanical strength and light transmittance without using a HIP device, a zirconia shaped body to obtain such a zirconia sintered body, and a zirconia pre-sintered body have also been proposed (Patent Documents 2 and 3).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-214168

[0008] Patent Document 2: International Publication No. 2020 / 179876

[0009] Patent Document 3: International Publication No. 2020 / 179877 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, the inventors conducted research and found that when using nanoparticles with an average particle size (average primary particle size) of less than 100 nm (e.g., zirconium oxide with an average primary particle size of less than 100 nm), as in Patent Documents 2 and 3, if the crystalline structure is simply kept small, a problem arises: a so-called structural color (hereinafter referred to as "opalescent") is produced, which selectively reflects or transmits specific wavelengths due to its uniform structure. Therefore, due to the use of nanoparticles, it is difficult to achieve an appearance close to that of natural teeth.

[0012] Therefore, the object of the present invention is to provide a zirconia composition with excellent light transmittance of the sintered body and capable of suppressing the opalescence of the sintered body, a zirconia pre-sintered body using the composition, a zirconia sintered body, and a manufacturing method for which they can be easily manufactured.

[0013] Solution for solving the problem

[0014] To achieve the above objectives, the inventors conducted repeated and diligent research, and discovered that by sintering the zirconia composition, the structural regularity of the zirconia sintered body is reduced, and wavelength-selective reflection and / or transmission are suppressed, resulting in a zirconia sintered body with both high light transmittance and low opalescence. The zirconia composition comprises zirconia particles and stabilizer particles capable of suppressing the phase transformation of zirconia. The average particle size (r1) of the aforementioned zirconia is 1–60 nm, and the average particle size (r2) of the stabilizer is 1–60 nm. The full width at half maximum (FWHM) of the peaks originating from the aforementioned stabilizer in the powder X-ray diffraction pattern based on CuKα rays is 0.05°–1.0°. The inventors further conducted repeated research, thereby completing this invention.

[0015] That is, the present invention relates to the following invention.

[0016] [1] A zirconium oxide composition comprising zirconium oxide particles and stabilizer particles capable of inhibiting the phase transformation of zirconium oxide.

[0017] The average particle size (r1) of the aforementioned zirconium oxide particles is 1–60 nm, and the average particle size (r2) of the aforementioned stabilizer particles is 1–60 nm.

[0018] The peak width at half maximum (FWHM) of the stabilizer-derived peaks in the powder X-ray diffraction pattern based on CuKα rays is 0.05° to 1.0°.

[0019] [2] According to the zirconium oxide composition of [1], the content of the stabilizer is 2 to 9 mol% relative to the total molar number of zirconium oxide and stabilizer.

[0020] [3] The zirconium oxide composition according to [1] or [2], wherein the aforementioned stabilizer is yttrium oxide.

[0021] [4] The zirconium oxide composition according to any one of [1] to [3], wherein the aforementioned zirconium oxide particles comprise a monoclinic crystal system.

[0022] [5] A zirconia pre-sintered body comprising zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia.

[0023] At least a portion of the aforementioned stabilizer is not dissolved in zirconium oxide, and the monoclinic crystal ratio f shown in the following mathematical formula (1) is... m The local presence of stabilizer in particles derived from stabilizers is 10–90 mol%, ranging from 50% to 98%.

[0024] f m =I 28 / (I 28 +I 30 )*100 (1)

[0025] (where f) m The percentage (%) of the monoclinic crystal system is represented in XRD measurements. 28 I represents the area intensity of the peak near 2θ = 28° where the main peak appears in the monoclinic crystal system. 30 This represents the area intensity of the peak near 2θ = 30° where the main peak appears in the tetragonal or cubic crystal system.

[0026] [6] According to the zirconia pre-fired body described in [5], the content of the stabilizer is 2 to 9 mol% relative to the total molar number of the aforementioned zirconia and stabilizer.

[0027] [7] The zirconia pre-burnt body according to [5] or [6], wherein the aforementioned stabilizer is yttrium oxide.

[0028] [8] The zirconia pre-sintered body according to any one of [5] to [7], wherein, in the sintered body with a thickness of 1.2 mm after sintering at 900 to 1400 °C for 120 minutes, the OP value calculated using the following mathematical formula (2) is less than 15.

[0029]

Mathematical Formula 1

[0030]

[0031] (where a) ＊ 透射 and b ＊ 透射 L*a*b* represents the color coordinates of the color system in transmitted light, where a ＊ 反射 and b ＊ 反射 (This represents the color coordinates of the L*a*b* color system in the reflected light).

[0032] [9] The zirconia pre-sintered body according to any one of [5] to [8], wherein the sintered body after sintering at 900 to 1400°C for 120 minutes has at least one peak in the particle size distribution based on the number of particles in the range of particle size greater than 70 nm and less than 100 nm, and contains 3 to 15% of particles with a particle size greater than 100 nm.

[0033]

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

[0034]

[11] The zirconia pre-sintered body according to any one of [5] to

[10] , wherein the first light transmittance ΔL1*(WB) of the first sintered body prepared by sintering at 1300°C for 120 minutes and the second light transmittance ΔL2*(WB) of the second sintered body prepared by sintering at 1300°C for 10 minutes satisfy the following mathematical formula (3) relationship.

[0035] ΔL2*(WB) / ΔL1*(WB)≥0.85 (3).

[0036]

[12] A method for manufacturing a zirconia pre-fired body, wherein the zirconia composition described in any one of [1] to [4] is used.

[0037]

[13] A zirconia sintered body comprising zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia.

[0038] The stabilizer content is 2-9 mol% relative to the total molar number of zirconium oxide and stabilizer. The ΔL*(WB) in the sintered body with a thickness of 1.2 mm is 5 or more, and the OP value calculated using the following mathematical formula (2) is less than 15.

[0039]

Mathematical Formula 2

[0040]

[0041] (where a) ＊ 透射 and b ＊ 透射 L*a*b* represents the color coordinates of the color system in transmitted light, where a ＊ 反射 and b ＊ 反射 (This represents the color coordinates of the L*a*b* color system in the reflected light).

[0042]

[14] The zirconia sintered body according to

[13] , wherein the aforementioned stabilizer is yttrium oxide.

[0043]

[15] The zirconia sintered body according to

[13] or

[14] , wherein the particle size distribution based on the number of particles has at least one peak in the range of particle size greater than 70 nm and less than 100 nm, and contains 3 to 15% of particles with a particle size greater than 100 nm.

[0044]

[16] A method for manufacturing zirconia sintered body, wherein the zirconia composition described in any one of [1] to [4] or the zirconia pre-sintered body described in any one of [5] to

[11] is used.

[0045]

[17] The method for manufacturing zirconia sintered bodies according to

[16] includes a step of sintering at 900 to 1400 °C.

[0046] The effects of the invention

[0047] According to the present invention, there is a zirconia composition that can provide excellent light transmittance of the sintered body and suppress opalescence of the sintered body, a zirconia pre-sintered body using the composition, and a zirconia sintered body, as well as a manufacturing method that can easily manufacture them.

[0048] According to the present invention, opalescence can be suppressed and light transmittance is excellent, thus providing a zirconia sintered body that can have an appearance closer to that of natural teeth.

[0049] Furthermore, according to the present invention, it is possible to provide a zirconia pre-sintered body that can supply such a zirconia sintered body and a manufacturing method that can easily manufacture the zirconia sintered body.

[0050] Brief description of the attached diagram

[0051] Figure 1 This is a particle size chart of the zirconium oxide composition involved in Example 1.

[0052] Figure 2 This is an XRD (X-ray diffraction) chart of the stabilizer in the zirconium oxide composition involved in Example 1.

[0053] Figure 3 This is the compositional distribution (SEM-EDX) of the crystalline structure of the zirconia pre-sintered body involved in Example 1.

[0054] Figure 4 The compositional distribution (SEM-EDX) of the crystalline structure of the zirconia pre-sintered body involved in Comparative Example 2 is shown.

[0055] Figure 5 This is a particle size chart of the zirconia sintered bodies involved in Example 1 and Comparative Example 2. Detailed Implementation

[0056] This invention comprises a zirconia composition containing zirconia particles and stabilizer particles capable of suppressing the phase transformation of zirconia. The average particle size (r1) of the zirconia is 1–60 nm, and the average particle size (r2) of the stabilizer is 1–60 nm. The full width at half maximum (FWHM) of the peaks originating from the stabilizer in a CuKα-ray-based powder X-ray diffraction pattern is 0.05°–1.0°. By using this zirconia composition, sintered zirconia bodies with low opalescence and excellent light transmittance can be obtained. Furthermore, the sintered zirconia bodies obtained using the zirconia composition of this invention exhibit excellent light transmittance even under short sintering times.

[0057] In addition, the present invention includes a zirconia pre-sintered body comprising zirconia and a stabilizer capable of suppressing the phase transformation of zirconia, wherein at least a portion of the stabilizer is not dissolved in zirconia, and the monoclinic crystal ratio f is shown in the following mathematical formula (1). m The content of the stabilizer is 50-98%, and the local presence of the stabilizer is 10-90 mol%. By using this zirconia pre-sintered body, a zirconia sintered body with excellent light transmittance and suppressed opalescence can be obtained.

[0058] f m =I 28 / (I 28 +I 30 )*100 (1)

[0059] (where f) m The percentage (%) of the monoclinic crystal system is represented in XRD measurements. 28 I represents the area intensity of the peak near 2θ = 28° where the main peak appears in the monoclinic crystal system. 30 This represents the area intensity of the peak near 2θ = 30° where the main peak appears in the tetragonal or cubic crystal system.

[0060] The following section will first describe the zirconium oxide composition.

[0061] [Zirconium oxide composition]

[0062] The zirconia composition of the present invention contains zirconia particles and stabilizer particles capable of inhibiting the zirconia phase transformation.

[0063] From the viewpoint of having the desired property that at least a portion of the stabilizer (hereinafter also referred to as "stabilizer") capable of suppressing the zirconia phase transformation is not dissolved in zirconia or the like, it is preferable to prepare and use zirconia particles and stabilizer particles capable of suppressing the zirconia phase transformation separately. Furthermore, from the perspective of suppressing the opalescence of the sintered body obtained using the zirconia composition, and from the perspective of having excellent light transmittance even when the zirconia pre-sintered body using the zirconia composition is sintered for a short time, the zirconia particles preferably contain a monoclinic crystal system.

[0064] By preparing and using individual particles separately, in combination with other manufacturing processes during the production of zirconia compositions, zirconia pre-sintered bodies, or zirconia sintered bodies, the crystallinity of the zirconia composition can be significantly improved. The stabilizer dissolves in the zirconia, initiating a phase transformation. This forms the periphery of the stabilizer, making it difficult to obtain a uniform structure composed of small particles in the sintered crystalline structure. Therefore, it can be inferred that the structural regularity of the zirconia sintered body is reduced, wavelength-selective reflection and / or transmission are suppressed, resulting in a zirconia sintered body with both high light transmittance and low opalescence.

[0065] 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 transformation 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. By making r1 and r2 60 nm or less, the crystalline structure after sintering is smaller, and the light transmittance is improved. In addition, 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. By making r1 and r2 1 nm or more, the agglomeration of primary particles can be suppressed. Any combination of these values ​​can also be used. 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 can be the same or different as long as they meet the above ranges. The aforementioned average primary particle size can be measured after pulverization. The method for measuring the average primary particle size is not particularly limited, for example, it can be measured by observation with a high-power electron microscope. Specifically, the methods described in the embodiments described later can be cited as examples.

[0066] In some implementations, a smaller r2 and a larger r1 result in a lower opalescence, which is preferable. In particular, when the ratio (r2 / r1) is less than 0.5, there is a tendency for a decrease in opalescence, so a smaller r2 and a larger r1 are preferred.

[0067] On the other hand, even in embodiments where r1 and r2 are close in value, when the content of the stabilizer is low, the frequency of the presence of the stabilizer in the zirconia composition is reduced, the crystal structure becomes uneven, and the opalescence can be reduced, which is therefore preferred.

[0068] Examples of embodiments where r1 and r2 are close values ​​include, for instance, a zirconium oxide composition with a ratio (r2 / r1) of 0.5 to 2 and a stabilizer content of 2.0 to 6.0 mol% relative to the total moles of zirconium oxide and stabilizer. In the aforementioned embodiments, the ratio (r2 / r1) can be 0.55 to 1.5. Furthermore, in the aforementioned embodiments, the stabilizer content can be 2.0 to 5.5 mol% relative to the total moles of zirconium oxide and stabilizer.

[0069] The shape of the peaks 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 tailed peak with a shoulder (e.g., a peak on the smaller particle size side and a tailed peak with a shoulder on the larger particle size side), or a leading peak with a shoulder (e.g., a peak on the larger particle size side and a leading peak with a shoulder on the smaller particle size side). Furthermore, within the range satisfying the aforementioned average particle size (r2), larger stabilizer particles result in less complete solid solution between the stabilizer and zirconia, leading to a decrease in opalescence; this is preferable from this perspective. The particle size distribution of the stabilizer particles can be determined by the method described in the examples described later.

[0070] From the viewpoint of achieving a crystalline structure that suppresses opalescence, the ratio (r2 / r1) of the average particle size (r1) of the zirconia particles to the average particle size (r2) of the stabilizer particles capable of suppressing the phase transformation of zirconia is preferably 0.1 to 10, more preferably 0.2 to 6. By setting the ratio (r2 / r1) to 0.1 or higher, the range of particle growth can be limited while the stabilizer is dissolved in the zirconia particles, resulting in a crystalline particle size that is less prone to opalescence in the sintered body, which is therefore preferred. Furthermore, by setting the ratio (r2 / r1) to 10 or lower, stabilizer inhomogeneity can be avoided, suppressing the decrease in light transmittance (ΔL*(WB)) caused by localized particle growth, which is also preferred.

[0071] From the viewpoint of preventing the sintering process from becoming substantially uniform and the resulting microstructure from becoming homogeneous and opalescent, it is preferable in the zirconia composition of the present invention that the aforementioned stabilizer is not completely dissolved in zirconia. Incomplete dissolution of the stabilizer in zirconia means that at least a portion of the stabilizer is not dissolved in zirconia. For example, by using an X-ray diffraction (XRD) pattern based on CuKα rays obtained from the zirconia composition, it can be confirmed that at least a portion of the stabilizer is not dissolved in zirconia. When a peak originating from the stabilizer is identified in the XRD pattern of the zirconia composition, it can be said that a stabilizer that is not dissolved in zirconia is present in the zirconia composition.

[0072] Furthermore, from the viewpoint of reducing opalescence while simultaneously producing a crystalline structure with improved light transmittance of the sintered body, the half-width at half-maximum (WHM) of the peaks originating from the stabilizer in the XRD pattern is 1.0° or less, preferably 0.8° or less, and more preferably 0.6° or less. Additionally, from the viewpoint of stabilizer composition distribution, the WHM is 0.05° or more, preferably 0.1° or more, and more preferably 0.2° or more. Any combination of these values ​​is acceptable as long as it falls within the range of 0.05° to 1.0°. For example, a WHM of 0.1° to 0.8° is preferred, and more preferably 0.2° to 0.6°.

[0073] By combining the range of the average particle size (r1) of the aforementioned zirconia particles, the range of the average particle size (r2) of the aforementioned stabilizer particles, and the half-peak width (FWHM) of the peaks originating from the aforementioned stabilizer (0.05°–1.0°), the monoclinic crystallinity f in the zirconia pre-sintered body can be increased. m With a content of 50% or more and 98% or less, the ΔL*(WB) of the zirconia sintered body can be 5 or more, and the OP value calculated using formula (2) can be less than 15.

[0074] By setting the full width at half maximum (FWHM) to the aforementioned range, the monoclinic crystallinity f in the zirconia pre-sintered body using the zirconia composition is... m With a content of 50-98%, the local presence of stabilizer in the particles derived from stabilizer can be adjusted to the desired range, so that the OP value calculated by formula (2) can be less than 15 in the sintered zirconia body after the zirconia pre-sintered body is sintered.

[0075] Here, the full width at half maximum (FWHM) in this specification refers to the width (in degrees) of the peak at a position where the peak intensity originating from the stabilizer is half that of a powder X-ray diffraction pattern based on CuKα rays. For example, the measurement conditions described in the examples described later can be used as the conditions for determining the FWHM.

[0076] The content of stabilizer in the zirconium oxide 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, relative to the total moles of zirconium oxide (zirconia (IV); ZrO2) and stabilizer. When it is 2 mol% or more, the cubic crystal system encapsulated within the sintered body increases, resulting in improved light transmittance, which is preferable from this perspective.

[0077] Furthermore, the content of the aforementioned stabilizer is preferably 9 mol% or less, more preferably 8.5 mol% or less, and even more preferably 8 mol% or less. When it is 9 mol% or less, the proportion of cubic crystals in the encapsulated crystalline system is not too high, which easily inhibits grain growth and prevents the crystalline structure from becoming too large, thus suppressing the decrease in light transmittance, and is therefore preferred.

[0078] The content of the aforementioned stabilizers can be set to a range resulting from any combination thereof. For example, the content of the aforementioned stabilizers is preferably 2 to 9 mol%, more preferably 3 to 8 mol%.

[0079] The aforementioned stabilizer is preferably capable of forming partially stabilized zirconium oxide. Examples of such stabilizers include, for instance, calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y₂O₃), cerium oxide (CeO₂), scandium oxide (Sc₂O₃), niobium oxide (Nb₂O₅), lanthanum oxide (La₂O₃), erbium oxide (Er₂O₃), and praseodymium oxide (Pr₆O₃). 11 Yttrium oxide is preferred from the viewpoint that, in combination with the aforementioned composition such as the half-width at half-maximum, the sintered body exhibits excellent light transmittance even during short-time sintering.

[0080] The content of stabilizer in the aforementioned composition can be quantified using common analytical methods. Examples include inductively coupled plasma (ICP) luminescence spectrophotometry, fluorescence X-ray analysis (XRF), and energy-dispersive or wavelength-dispersive X-ray analysis (SEM-EDX or SEM-WDX) attached to a scanning electron microscope.

[0081] As needed, the zirconium oxide composition of the present invention may contain additives such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (Al2O3), titanium dioxide (TiO2), and silicon dioxide (SiO2) (excluding the aforementioned stabilizers). These components may be used individually or in combination of two or more.

[0082] Examples of pigments include oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Er.

[0083] Examples of the aforementioned composite pigments include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, and (Co,Zn)Al2O4.

[0084] The zirconia composition of the present invention may contain a fluorescent agent. By including a fluorescent agent in the zirconia composition, the zirconia sintered body exhibits fluorescence. There is no particular limitation on the type of fluorescent agent; one or more substances capable of emitting fluorescence at any wavelength can be used. Examples of such fluorescent agents include those containing a metallic element. Examples of such metallic elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain only one of these metallic elements or may contain two or more. Among these metallic elements, Ga, Bi, Eu, Gd, and Tm are preferred, and Bi and Eu are more preferred. Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the aforementioned metallic elements.

[0085] Alternatively, fluorescent agents can also be Y₂SiO₅:Ce, Y₂SiO₅:Tb, (Y,Gd,Eu)BO₃, Y₂O₃:Eu, YAG:Ce, ZnGa₂O₄:Zn, BaMgAl 10 O 17 Eu et al.

[0086] The content of the fluorescent agent in the zirconia composition is not particularly limited and can be appropriately adjusted according to the type of fluorescent agent or the intended use of the zirconia sintered body. However, from the viewpoint of preferably using it as a dental restoration, the 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, relative to 100% by mass of zirconia contained in the zirconia composition, when calculated based on the oxides of the metal elements contained in the fluorescent agent. Furthermore, the content of the fluorescent agent, when calculated based on the oxides of the metal elements contained in the fluorescent agent, is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. By keeping this content at or above the aforementioned lower limit, the fluorescence is not inferior even compared to natural human teeth. Furthermore, by keeping this content at or below the aforementioned upper limit, the reduction in translucency and mechanical strength can be suppressed.

[0087] The zirconia composition of the present invention may include a binder. Examples of binders include polyvinyl alcohol, methylcellulose, carboxymethyl cellulose, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, ethyl cellulose, etc. To improve light transmittance, the binder content in the zirconia composition of the present invention is preferably 10% by mass or less relative to 100% by mass of zirconia, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0088] [Method for manufacturing zirconium oxide composition]

[0089] The zirconia composition of the present invention preferably includes a step of manufacturing zirconia particles, a step of manufacturing stabilizer particles, and a step of manufacturing a powder containing zirconia-based particles. Hereinafter, particles containing zirconia particles and stabilizer particles capable of inhibiting the phase transformation of zirconia will be referred to as "zirconia-based particles" based on the premise that the amount of zirconia particles is sufficiently greater than the amount of stabilizer particles.

[0090] Method for manufacturing zirconium oxide particles and stabilizer particles

[0091] The method for preparing the zirconia particles contained in the zirconia composition of the present invention is not particularly limited, and can employ, for example, a break-down process to micronize coarse particles by pulverizing or crushing them; or a building-up process that utilizes nucleation and growth processes to synthesize particles from atoms or ions. Hereinafter, examples of methods for preparing zirconia particles will be provided. Except as specifically described, the methods for preparing zirconia particles can also be used in the same way as methods for preparing stabilizer particles.

[0092] The pulverization process can be carried out by pulverizing, for example, using a ball mill or bead mill. The pulverization process can be used as a method for manufacturing zirconia particles. On the other hand, as a method for manufacturing stabilizer particles, the pulverization process is preferred from the perspective of improving the crystallinity of yttrium oxide and easily adjusting the full width at half maximum (FWHM) of the peaks originating from the stabilizer to the desired range. In the pulverization process, stabilizer particles can be pulverized to obtain particles with the desired average particle size. Pulverization preferably uses a pulverizing medium with a small particle size. For example, pulverizing media with a particle size of 100 μm or less are preferred.

[0093] In addition, from the perspective of obtaining the desired ΔL * (WB) From the perspective of adjusting r1 and r2, it is preferable to classify the resulting zirconia particles after crushing the coarse particles. Classification can be performed using known methods and apparatus. Known methods include, for example, using the difference in settling velocity caused by particle size-dependent dispersibility for sifting, or accelerating settling using a centrifuge. Known apparatuses include, for example, porous membranes (membrane filters with pore sizes of 100 nm, etc.) and classification devices (wet classification devices, dry classification devices), etc.

[0094] In particular, from the viewpoint of easily improving the crystallinity of the zirconia composition and easily adjusting the half-peak width of the peaks derived from the stabilizer in the XRD pattern to the range desired by the present invention, it is preferable to use a solid stabilizer (e.g., yttrium oxide) as the raw material in the method for manufacturing stabilizer particles.

[0095] On the other hand, examples of construction processes include: gas-phase thermal decomposition methods that precipitate oxides by vaporizing oxyacid salts or organometallic compounds with high vapor pressure metal ions and then thermally decomposing them; gas-phase reaction methods that synthesize by gas-phase chemical reactions of gaseous metal compounds with high vapor pressure and reaction gases; evaporation and concentration methods that condense vapors into particulates by heating the raw materials, then rapidly cooling them in an inert gas at a specified pressure; melt methods that form molten liquid into small droplets and then solidify them by cooling to form powders; solvent evaporation methods that increase the concentration in a liquid by evaporating the solvent to create a supersaturated state and precipitate the compounds; and precipitation methods that precipitate insoluble compounds such as oxides and hydroxides by reacting with a precipitant, hydrolyzing the solute to create a supersaturated state, and then undergoing a nucleation-growth process.

[0096] Precipitation methods can be further subdivided into: homogeneous precipitation methods, which generate precipitants in solutions through chemical reactions to eliminate local unevenness in precipitant concentration; coprecipitation methods, which simultaneously precipitate multiple metal ions coexisting in a liquid by adding precipitants; hydrolysis methods, which obtain oxides or hydroxides from metal salt solutions, metal alkoxides, and other alcohol solutions through hydrolysis; and solvothermal synthesis methods, which obtain oxides or hydroxides from high-temperature and high-pressure fluids. Solvothermal synthesis methods can be further subdivided into: hydrothermal synthesis methods using water as a solvent; and supercritical synthesis methods using supercritical fluids such as water and carbon dioxide as solvents.

[0097] It should be noted that, in this invention, for zirconium oxide particles and stabilizer particles, from the perspective that the respective particles have the desired average particle size (r1 and r2), it is preferable not to use the co-precipitation method using zirconium oxide and stabilizer.

[0098] Furthermore, from the perspective of improving the crystallinity of the zirconia composition, it is preferable that the stabilizer particles (e.g., yttrium oxide particles) are not manufactured in the liquid phase. When stabilizer particles are prepared in the liquid phase, crystallinity cannot be sufficiently improved, and the full width at half maximum (FWHM) of the peaks derived from the stabilizer in the XRD pattern cannot be within the range desired by this invention.

[0099] Regarding any fabrication process, accelerating the precipitation rate is preferred to obtain finer zirconia particles. Furthermore, achieving the desired ΔL... * From the perspective of (WB) and linear light transmittance, it is preferable to classify the obtained zirconia particles. Classification can be performed using known methods and apparatus. Examples of known apparatus include porous membranes (membrane filters with pore sizes of 100 nm, etc.) and classification devices (wet classification devices, dry classification devices), etc.

[0100] Zirconium sources used in the fabrication process can include, for example, nitrates, acetates, chlorides, and alkoxides. Specifically, examples of zirconium sources include zirconium dichloride, zirconium acetate, and zirconium oxynitrate.

[0101] When zirconia particles are manufactured using methods such as fabrication processes, as long as the average particle size of the zirconia particles is within the desired range, they can be used in the process of manufacturing powders containing zirconia particles in the form of a slurry containing zirconia particles without drying treatment. There are no particular limitations on the method for preparing the slurry containing the aforementioned zirconia particles; for example, it can be a slurry obtained through the aforementioned crushing or fabrication processes, or it can be a commercially available slurry.

[0102] The method for manufacturing the zirconia composition of the present invention can, for example, control the average particle size (r1 and r2) by a pulverizing process. Zirconia and stabilizer can be pulverized separately to form zirconia particles and stabilizer particles having the desired average particle size (r1 and r2). When pulverization is performed simultaneously, the stabilizer may sometimes undergo solid dissolution due to the energy of pulverization; therefore, a manufacturing method with fewer mixing and pulverizing steps is preferred. The pulverizing method is not particularly limited and can also be media pulverization such as ball mills or bead mills, or media-free pulverization such as wet or dry JET pulverization.

[0103] As mentioned above, for zirconium oxide particles and stabilizer particles, the size can be controlled by grading, crushing, etc., depending on the manufacturing method, so that each particle has the desired average particle size (r1 and r2).

[0104] In the grinding process, additives can be added to improve grinding efficiency and inhibit solid solution. Additives include dispersants, emulsifiers, defoamers, plasticizers, etc.

[0105] Examples of dispersants include ammonium polycarboxylate (such as triammonium citrate), ammonium polyacrylate, acrylic copolymer resins, acrylate copolymers, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (such as polyoxyethylene lauryl ether phosphate and polyoxyethylene alkyl ether phosphate), nonionic surfactants, trioleic acid glycerides, amine surfactants, and oligosaccharide alcohols.

[0106] Examples of emulsifiers include alkyl ethers, phenyl ethers, sorbitol derivatives, and ammonium salts.

[0107] Examples of defoaming agents include alcohols, polyethers, polyethylene glycols, silicones, and waxes.

[0108] Examples of plasticizers include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0109] • Method for manufacturing powders containing zirconium oxide particles

[0110] The powder containing zirconia particles (mixed powder) is obtained by mixing zirconia particles with stabilizer particles capable of suppressing the phase transformation of zirconia. The method of mixing the zirconia particles with the stabilizer particles is not particularly limited, and examples include wet mixing and dry mixing. As described above, the zirconia particles can be in the form of a slurry containing zirconia particles, and the stabilizer particles can be in the form of a slurry containing stabilizer particles. Therefore, as some embodiments, examples include: mixing a slurry containing zirconia particles and a slurry containing stabilizer particles to obtain a slurry containing zirconia particles, then drying the slurry containing zirconia particles to obtain a powder containing zirconia particles; or mixing zirconia particles (powder) and a slurry containing stabilizer particles to obtain a slurry containing zirconia particles, then drying the slurry containing zirconia particles to obtain a powder containing zirconia particles, etc.

[0111] There are no particular limitations on the preparation method of the powder containing zirconia particles. However, to obtain a more uniform zirconia sintered body with excellent physical properties, the powder containing zirconia particles is preferably obtained by drying the aforementioned slurry containing zirconia particles. This slurry, provided for drying, may further contain fluorescent agents and / or colorants and / or light transmittance modifiers.

[0112] The drying method is not particularly limited and can include, for example, spray drying, supercritical drying, freeze drying, hot air drying, and vacuum drying. Among these, spray drying, supercritical drying, and freeze drying are preferred, more preferably, spray drying and supercritical drying, and even more preferably, spray drying, based on the ability to suppress particle aggregation during drying and obtain a denser zirconia sintered body.

[0113] The slurry containing zirconia particles supplied for drying can be a slurry in which water is the dispersion medium. From the perspective of being able to suppress the aggregation of particles during drying and to obtain a denser zirconia sintered body, a slurry in which an organic solvent or other dispersion medium other than water is preferred.

[0114] Examples of organic solvents include, for instance, 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, glycerol, and other alcohols; acetone, methyl ethyl ketone, and other ketones; tetrahydrofuran, diethyl ether, diisopropyl ether, 1,4-dioxane, dimethoxyethane, and other ethers (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)); ethyl acetate, butyl acetate, and other esters; hexane, toluene, and other hydrocarbons; chloroform, carbon tetrachloride, and other halogenated hydrocarbons. These organic solvents can be used individually or in combination of two or more. Among these, considering both safety to organisms and ease of removal, the organic solvent is preferably a water-soluble organic solvent, and more preferably ethanol, 2-propanol, 2-methyl-2-propanol, 2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol, propylene glycol monomethyl ether acetate, acetone, and tetrahydrofuran.

[0115] Furthermore, especially when spray drying is employed, it is preferable that the dispersion medium for the slurry containing zirconia particles being dried contains a liquid with a surface tension of 50 mN / m or less at 25°C. This helps to suppress particle aggregation during drying, resulting in 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.

[0116] The surface tension at 25°C can be determined using values ​​described, for example, in the Handbook of Chemistry and Physics. For liquids not described therein, values ​​described in International Publication No. 2014 / 126034 can be used. For liquids not described in either of these publications, known measurement methods can be used, such as the ring method or the Wilhelmy method. The surface tension at 25°C is preferably measured using an automatic surface tension meter, the "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd., or the "SIGMA702" manufactured by KSV INSTRUMENTS LTD.

[0117] As the liquid described above, an organic solvent having the aforementioned surface tension can be used. The organic solvent can be one of the solvents described above that has the aforementioned surface tension, preferably selected from at least one of methanol, ethanol, 2-methoxyethanol, 1,4-dioxane, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol, more preferably selected from at least one of methanol, ethanol, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol, based on the principle that it can suppress particle aggregation during drying and obtain a denser zirconia sintered body.

[0118] From the perspective that it can suppress the aggregation of particles during drying and obtain a denser zirconia sintered body, the content of the above-mentioned liquid in the dispersion medium is preferably 50% by mass or more, more preferably 80% by mass or more, further preferably 95% by mass or more, and particularly preferably 99% by mass or more.

[0119] Slurries with a dispersion medium other than water can be obtained by replacing the dispersion medium in a slurry with an aqueous dispersion medium (hereinafter also referred to as "aqueous slurry"). The method of displacement is not particularly limited; for example, adding a dispersion medium other than water (such as an organic solvent) to an aqueous slurry followed by water distillation can be used. During water distillation, some or all of the dispersion medium other than water can be removed together. This addition of the dispersion medium other than water and the water distillation can be repeated multiple times. Alternatively, a method can be used where a dispersion medium other than water is added to an aqueous slurry, followed by precipitation of the dispersed phase. Furthermore, for aqueous slurries, after replacing the dispersion medium with a specific organic solvent, further displacement can be performed using another organic solvent.

[0120] It should be noted that while fluorescent agents can be added after the dispersion medium has been replaced, it is preferable to add them before the dispersion medium has been replaced, in order to obtain a more uniform zirconia sintered body with superior physical properties. Similarly, when the slurry contains colorants and / or light transmittance modifiers, they can be added after the dispersion medium has been replaced, but it is preferable to add them before the dispersion medium has been replaced, in order to obtain a more uniform zirconia sintered body with superior physical properties.

[0121] The slurry containing zirconia particles supplied for drying can undergo heat- and pressure-based dispersion treatments such as reflux treatment and hydrothermal treatment. Alternatively, the slurry containing zirconia particles supplied for the drying process can be mechanically dispersed using roller mills, colloid mills, high-pressure jet dispersers, ultrasonic dispersers, vibratory mills, planetary mills, bead mills, etc. Only one of the above treatments may be used, or two or more may be employed.

[0122] The slurry containing zirconia particles supplied for drying may further include one or more of the following components: binder, dispersant, emulsifier, defoamer, pH adjuster, lubricant, etc. By including these other components (especially binders, dispersants, defoamers, etc.), particle aggregation can sometimes be suppressed during drying, resulting in a denser zirconia sintered body.

[0123] As dispersants, emulsifiers, and defoamers, examples can be made of substances identical to those exemplified in the pulverizing process of the aforementioned method for manufacturing zirconium oxide particles.

[0124] Examples of pH adjusters include ammonia, ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide), alkali metal salts, and alkaline earth metal salts.

[0125] Examples of lubricants include polyoxyethylene alkyl ethers and waxes.

[0126] From the perspective of suppressing particle aggregation during drying and obtaining a denser zirconia sintered body, the water content in the slurry containing zirconia particles supplied for drying is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less. This water content can be measured using a Karl Fischer moisture meter.

[0127] The drying conditions in the above-described drying methods are not particularly limited, and known drying conditions can be appropriately adopted. It should be noted that when using organic solvents as the dispersion medium, to reduce the risk of explosion during drying, it is preferable to perform drying in the presence of a non-flammable gas, and more preferably in the presence of nitrogen.

[0128] There are no particular limitations on the supercritical fluid used in supercritical drying; for example, water or carbon dioxide can be used. However, carbon dioxide is preferred as it can suppress particle aggregation and produce a denser zirconia sintered body.

[0129] The powder containing zirconia particles obtained as described above can be used as a zirconia composition containing zirconia particles and stabilizer particles capable of inhibiting the phase transformation of zirconia. Furthermore, in this invention, the zirconia composition can also be formed into a molded article through a molding process.

[0130] A molded body is a material formed by applying external force to powder containing zirconium oxide particles. Since it is a material before firing, it means that necking (adhesion) has not occurred.

[0131] There is no particular limitation on the type of forming process. From the perspective of easily obtaining the zirconia shaped body of the present invention, and further, the zirconia pre-sintered body and zirconia sintered body of the present invention, the forming process is preferably at least one of the following processes:

[0132] (i) A process of casting a slurry containing zirconium oxide particles;

[0133] (ii) The process of gel casting a slurry containing zirconia particles;

[0134] (iii) A process of pressing powder containing zirconium oxide particles into shape;

[0135] (iv) A process for molding a composition comprising zirconium oxide particles and a resin; and

[0136] (v) A process of polymerizing a composition comprising zirconium oxide particles and polymerizable monomers.

[0137] The preferred method is a forming process that involves shaping zirconia particles, polyols, and binders to obtain a zirconia molded body.

[0138] (i) casting

[0139] When manufacturing zirconia molded bodies by means of a process of casting a slurry containing zirconia particles, there are no particular limitations on the specific casting method. For example, a method can be used where the slurry containing zirconia particles is poured into a mold and then dried.

[0140] From the perspectives of facilitating the flow of slurry into the mold, preventing excessive drying time, and increasing the number of times the mold can be used, the content of the dispersion medium in the slurry containing zirconium oxide particles is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less.

[0141] The slurry can be poured into the mold under normal pressure, but from a production efficiency standpoint, it is preferable to do so under pressure. There are no particular restrictions on the type of mold used in flow casting; porous molds made of materials such as plaster, resin, or ceramic can be used. Porous molds made of resin or ceramic offer excellent durability.

[0142] The slurry containing zirconia particles used in casting may further contain one or more of the following components: binder, plasticizer, dispersant, emulsifier, defoamer, pH adjuster, lubricant, etc.

[0143] (ii) Gel filling

[0144] When manufacturing a zirconia molded body by means of a process of gel casting a slurry containing zirconia particles, there are no particular limitations on the specific method of gel casting. For example, a method can be used to gel the slurry containing zirconia particles and a fluorescent agent in a mold, shape it to obtain a wet body, and then dry it.

[0145] From the perspective of preventing excessive drying time and suppressing cracks during drying, the content of the dispersion medium in the slurry containing zirconium oxide particles is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less.

[0146] The aforementioned gelation can be achieved, for example, by adding a gelling agent, or by polymerizing the product after adding a polymerizable monomer. There are no particular restrictions on the type of mold used; for example, porous molds made of plaster, resin, ceramic, etc., or non-porous molds made of metal, resin, etc., can be used.

[0147] There is no limitation on the type of gelling agent; for example, water-soluble gelling agents can be used. Specifically, agarose, gelatin, etc., are preferred. A single gelling agent can be used, or two or more can be used in combination. From the viewpoint of suppressing 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 mixing with the gelling agent.

[0148] Furthermore, there are no particular limitations on the types of polymerizable monomers, and examples 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-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N,N-bis(2-hydroxyethyl)(meth)acrylamide. A single polymerizable monomer can be used, or two or more monomers can be used in combination.

[0149] From the viewpoint of suppressing 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 blending the polymerizable monomer.

[0150] In the case of gelation by polymerization of polymerizable monomers, polymerization is preferably carried out using a polymerization initiator. The type of polymerization initiator is not particularly limited, but photopolymerization initiators are particularly preferred. As a photopolymerization initiator, it is appropriate to select and use from those commonly used in industry, with photopolymerization initiators used in dental applications being preferred.

[0151] Specific examples of photopolymerization initiators include (bis)acylphosphine oxides (including salts), thioxanthones (including quaternary ammonium salts), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ethers, and α-aminoketone compounds. A single photopolymerization initiator can be used, or two or more can be used in combination. Among these photopolymerization initiators, at least one selected from (bis)acylphosphine oxides and α-diketones is preferred. This allows polymerization (gelation) to occur in both the ultraviolet (including near-ultraviolet) and visible light regions, and in particular, polymerization (gelation) can be fully achieved even when using any light source, such as Ar lasers, He-Cd lasers, halogen lamps, xenon lamps, metal halide lamps, LEDs, mercury lamps, and fluorescent lamps.

[0152] Among the aforementioned (bis)acylphosphine oxides, examples of acylphosphine oxides include 2,4,6-trimethylbenzoyl diphenylphosphine oxide (commonly known as "TPO"), 2,6-dimethoxybenzoyl diphenylphosphine oxide, 2,6-dichlorobenzoyl diphenylphosphine oxide, 2,4,6-trimethylbenzoyl methoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyl ethoxyphenylphosphine oxide, 2,3,5,6-tetramethylbenzoyl diphenylphosphine oxide, benzoyl di(2,6-dimethylphenyl)phosphonate, sodium salt of 2,4,6-trimethylbenzoyl phenylphosphine oxide, potassium salt of 2,4,6-trimethylbenzoyl diphenylphosphine oxide, and ammonium salt of 2,4,6-trimethylbenzoyl diphenylphosphine oxide.

[0153] Among the aforementioned (bis)acylphosphine oxides, examples of 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 are included. Furthermore, compounds described in Japanese Patent Application Publication No. 2000-159621 may also be used.

[0154] Among these (bis)acylphosphine oxides, sodium salts of 2,4,6-trimethylbenzoyl diphenylphosphine oxide, 2,4,6-trimethylbenzoyl methoxyphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and 2,4,6-trimethylbenzoyl phenylphosphine oxide are preferred.

[0155] Examples of α-diketones include diacetyl, biphenylyl, camphorquinone, 2,3-pentanedione, 2,3-octanedione, 9,10-phenanthroquinone, 4,4'-oxybiphenylyl, and acenaphthoquinone. Among these, camphorquinone is preferred, especially when using light sources in the visible light region.

[0156] The slurry containing zirconia particles used in gel casting, like the slurry used in flow casting, may further contain one or more of the following components: binders, plasticizers, dispersants, emulsifiers, defoamers, pH adjusters, lubricants, etc.

[0157] There are no particular limitations on the drying method used to dry the shaped wet body. Examples include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. One or more of these methods can be used. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred to prevent cracking during drying.

[0158] (iii) Pressure forming

[0159] When manufacturing zirconia molded articles by means of a process involving the pressure forming of powder containing zirconia particles, the specific method of pressure forming is not particularly limited, and a known pressure forming machine can be used. Examples of specific pressure forming methods include uniaxial pressure forming. Furthermore, to increase the density of the resulting zirconia molded article, it is preferable to further perform cold isostatic pressing (CIP) treatment after uniaxial pressure forming.

[0160] The powder containing zirconia particles used in pressure molding may further contain one or more of the following components: binder, plasticizer, dispersant, emulsifier, defoamer, pH adjuster, lubricant, etc. These components may be mixed during powder preparation.

[0161] (iv) Molding of compositions containing resins

[0162] When manufacturing a zirconia molded body using a method that includes a process of molding a composition comprising zirconia particles and resin, the specific method used for molding the composition is not particularly limited, and can be, for example, injection molding, casting molding, extrusion molding, etc. Alternatively, methods for molding the composition using hot melt dispersive molding (FDM), inkjet printing, powder / binder lamination, and other lamination molding methods (3D printing, etc.) can be used. Among these molding methods, injection molding and casting molding are preferred, with injection molding being more preferred.

[0163] The type of resin is not particularly limited, but resins that function as adhesives are preferred. Specific examples of such resins include, for instance, alkane waxes, polyvinyl alcohol, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, atactic polypropylene, methacrylic resins, and fatty acids such as stearic acid. These resins can be used individually or in combination of two or more.

[0164] The composition comprising zirconia particles and resin may further comprise one or more of the following other components: plasticizer, dispersant, emulsifier, defoamer, pH adjuster, lubricant, etc.

[0165] (v) Polymerization of compositions containing polymerizable monomers

[0166] By polymerizing a composition containing zirconia particles and polymerizable monomers, the polymerizable monomers in the composition can be polymerized to solidify the composition. When manufacturing a zirconia molded body using a method incorporating this polymerization step, the specific method is not particularly limited; for example, (a) a method of polymerizing the composition containing zirconia particles and polymerizable monomers in a mold; or (b) a photolithography (stereolithography; SLA) method using the composition containing zirconia particles and polymerizable monomers, etc., can be employed. Of these, (b) the photolithography method is preferred. According to the photolithography method, a shape corresponding to the desired shape in the final zirconia sintered body can be imparted at the time of manufacturing the zirconia molded body. Therefore, this photolithography method is sometimes suitable, particularly when the zirconia sintered body of the present invention is used as a dental material such as dental restorations.

[0167] The type of polymerizable monomer in the above-mentioned composition comprising zirconia particles and polymerizable monomers is not particularly limited, and may be any of the following: monofunctional (meth)acrylates, monofunctional (meth)acrylamides, etc.; and polyfunctional polymerizable monomers such as difunctional aromatic compounds, difunctional aliphatic compounds, and trifunctional or higher compounds. One type of polymerizable monomer may be used alone, or two or more types may be used. Among these, polyfunctional polymerizable monomers are preferred, especially when using photoforming methods, etc.

[0168] Examples of monofunctional (meth)acrylates include 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, erythritol mono(meth)acrylate, and other (meth)acrylates containing hydroxyl groups; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, etc. Alkyl methacrylates such as tert-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, lauryl methacrylate, cetyl methacrylate, and stearyl methacrylate; alicyclic methacrylates such as cyclohexyl methacrylate and isobornyl methacrylate; methacrylates containing aromatic groups such as benzyl methacrylate and phenyl methacrylate; and methacrylates with functional groups such as 2,3-dibromopropyl methacrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, and 11-(meth)acryloyloxyundecyltrimethoxysilane.

[0169] 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.

[0170] Among these monofunctional polymerizable monomers, from the viewpoint of excellent polymerizability, (meth)acrylamide is preferred, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.

[0171] Examples of difunctional aromatic compounds 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, and 2,2-bis(4-(meth)acryloyloxypentethoxyphenyl)propane. (Meth)acrylates of 2,2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, 1,4-bis(2-(meth)acryloyloxyethyl)phenylmethylenetetramethacrylate, etc. Among these, Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles. Among 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average molar number of ethoxy addition: 2.6, commonly referred to as "D-2.6E") is preferred.

[0172] Examples of difunctional 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, butanediol 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. Acrylates, 1,6-hexanediol di(meth)acrylate, 2-ethyl-1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,2-bis(3-methacryloyloxy-2-hydroxypropoxy)ethane, 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate (commonly referred to as "UDMA"), etc., are all meth acrylates. Among these, triethylene glycol dimethacrylate (commonly referred to as "TEGDMA") and 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate are preferred from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles.

[0173] Examples of compounds with trifunctionality or higher include 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-(aminocarboxyl)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacetoxy-2,2,6,6-tetra(meth)acryloxymethyl-4-oxaheptane, etc. Among these, from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxyl)propane-1,3-diol]tetramethacrylate and 1,7-diacetoxy-2,2,6,6-tetracetoxymethyl-4-oxaheptane are preferred.

[0174] In either of the methods described in (a) and (b) above, polymerization of the composition is preferably carried out using a polymerization initiator, and the composition preferably further comprises a polymerization initiator. The type of polymerization initiator is not particularly limited, but photopolymerization initiators are particularly preferred. As a photopolymerization initiator, it is appropriate to select and use from those commonly used in industry, with photopolymerization initiators used in dental applications being preferred. Specific examples of photopolymerization initiators are the same as those described above in the instructions for gel casting, and are omitted here for repetition.

[0175] The composition comprising zirconia particles and polymerizable monomers may further comprise one or more of the following other components: plasticizers, dispersants, emulsifiers, defoamers, pH adjusters, lubricants, etc.

[0176] When manufacturing zirconia molded bodies using a photoforming method that employs a composition comprising zirconia-based particles and polymerizable monomers, the specific method of photoforming is not particularly limited, and known methods can be appropriately employed. For example, the following method can be used: by using a photoforming device, photopolymerizing a liquid composition using ultraviolet light, laser, or the like, thereby sequentially forming layers with the desired shape, thus obtaining the desired zirconia molded body.

[0177] When obtaining zirconia molded bodies by photoforming, from the viewpoint of subsequent sintering, the content of zirconia particles in the composition comprising zirconia particles and polymerizable monomers is preferably as high as possible. Specifically, the content of zirconia particles in the composition is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and particularly preferably 50% by mass or more. On the other hand, in photoforming, based on its layering principle, the viscosity of the composition is preferably within a certain specified range. Therefore, the content of zirconia particles in the above composition is preferably 90% by mass or less, more preferably 80% by mass or less, further preferably 70% by mass or less, and particularly preferably 60% by mass or less. In the case of implementing a restricted liquid surface method to sequentially form zirconia molded bodies layer by layer by curing the layers through light irradiating the bottom surface of the container from the lower side, the viscosity adjustment of the composition sometimes becomes particularly important in order to ensure that the cured layer rises by only one layer and flows smoothly between the lower surface of the cured layer and the bottom surface of the container to form the next layer.

[0178] Regarding the specific viscosity of the above composition, measured at 25°C, it 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. In this composition, there is a tendency for the viscosity to increase as the content of zirconia particles increases. Therefore, it is preferable to appropriately adjust the balance between the zirconia particle content and viscosity in the above composition, taking into account factors such as the performance of the photoforming apparatus used and the balance between the photoforming speed and the accuracy of the resulting zirconia molded body. It should be noted that this viscosity can be measured using an E-type viscometer.

[0179] In the method for manufacturing the zirconia molded article of the present invention, in order to further increase the density of the zirconia molded article, a CIP treatment can be performed after humidifying the zirconia molded article. In the case of pressure molding, the powder containing zirconia particles can be humidified before pressure molding, and then pressure molding can be performed. The humidification method can be any known method without any limitation; water can be sprayed or applied using a humidifier or a constant temperature and humidity device. The increase in moisture content due to the humidification treatment depends on the particle size of the contained zirconia particles, etc., but relative to the mass of the powder before humidification (powder before humidification treatment) and the molded article, it is preferably more than 2% by mass, more preferably more than 3% by mass, further preferably more than 4% by mass, particularly preferably more than 5% by mass, and preferably 15% by mass or less, more preferably 13% by mass or less, and further preferably 11% by mass or less. It should be noted that the increase in moisture based on the humidification treatment can be calculated as follows: subtract the mass of the powder and the molded body before humidification from the mass of the humidified powder (powder after humidification treatment) and the molded body, and then divide the resulting value by the mass of the powder and the molded body before humidification to obtain the percentage.

[0180] [Zirconium oxide pre-sintered body]

[0181] As another embodiment of the present invention, a zirconia pre-sintered body can be provided, which comprises zirconia and a stabilizer that can suppress the phase transformation of zirconia, wherein at least a portion of the stabilizer is not dissolved in zirconia, and the monoclinic crystal ratio f is shown in the following mathematical formula (1). m The content of stabilizer is 50-98%, and the local presence of stabilizer is 10-90 mol%.

[0182] f m =I 28 / (I 28 +I 30 )*100 (1)

[0183] (where f) m The percentage (%) of the monoclinic crystal system is represented in XRD measurements. 28 I represents the area intensity of the peak near 2θ = 28° where the main peak appears in the monoclinic crystal system. 30 This represents the area intensity of the peak near 2θ = 30° where the main peak appears in the tetragonal or cubic crystal system.

[0184] By using this zirconia pre-sintered body, a zirconia sintered body with excellent light transmittance and suppressed opalescence can be obtained even during short-time sintering.

[0185] Zirconia pre-sintered body can serve as a precursor (intermediate product) for zirconia sintered body. In this specification, zirconia pre-sintered body refers to a substance in which zirconia particles are necked together (adhered) and not fully sintered. The shape of zirconia pre-sintered body is not particularly limited and can be blocky, disc-shaped, etc.

[0186] In addition, zirconia pre-fired bodies also include materials obtained through forming processes.

[0187] Zirconia pre-fired bodies also include precursors for dental products (such as crown-shaped fittings) obtained by processing pre-fired zirconia discs using CAD / CAM (computer-aided design / computer-aided manufacturing) systems, prior to sintering.

[0188] In the zirconia pre-calcined body of the present invention, the monoclinic crystal system f m It refers to the ratio of the monoclinic crystal system in zirconium oxide to the total amount of crystal systems (monoclinic, tetragonal and cubic) present in zirconium oxide, calculated by formula (1).

[0189] Monoclinic crystallization rate f m For example, it can be calculated from the above equation (1) based on the peaks of the powder X-ray diffraction (XRD) pattern utilizing CuKα rays.

[0190] In the zirconia pre-calcined body of the present invention, the monoclinic crystallinity f m The total content of monoclinic, tetragonal, and cubic crystal systems is 50% or more, preferably 55% or more, more preferably 60% or more, and even more preferably 65% ​​or more. Furthermore, from the viewpoint of easily suppressing opalescence in the sintered body after sintering, the monoclinic crystal ratio f... m The content is 98% or less, preferably 94% or less, more preferably 91% or less, and even more preferably 87% or less. It can also be any combination thereof. For example, it is preferably 50-98%, more preferably 55-94%, even more preferably 60-91%, and most preferably 65-87%. The monoclinic crystallinity f in the zirconia pre-sintered body can be considered... m It also helps to increase the shrinkage temperature and shorten the sintering time (even in short sintering times, the light transmittance is excellent).

[0191] Monoclinic crystallinity f in zirconia pre-sintered body m The monoclinic crystal ratio f in the target sintered zirconia body can be adjusted by the manufacturing process or by using a zirconia composition containing a specified amount of zirconia particles (powder) with a monoclinic crystal system. m .

[0192] In the XRD pattern of the zirconia pre-sintered body, if a peak originating from the stabilizer is identified, then the zirconia pre-sintered body contains stabilizer that is not dissolved in zirconia. If all the stabilizer is dissolved, then essentially no peak originating from the stabilizer can be identified in the XRD pattern. However, depending on conditions such as the crystallization state of the stabilizer, even if no stabilizer peak is found in the XRD pattern, the stabilizer may sometimes be insoluble in zirconia. If the predominant crystal system of zirconia is tetragonal and / or cubic, and no stabilizer peak is found in the XRD pattern, then it can be considered that most, essentially all, of the stabilizer is dissolved in zirconia. "Predominant crystal system is tetragonal and / or cubic" means that the proportion of tetragonal and / or cubic crystal systems relative to the total amount of crystal systems (monoclinic, tetragonal, and cubic) present in zirconia is 50% or more. In the zirconia pre-sintered body of the present invention, all of this stabilizer may be insoluble in zirconia.

[0193] It should be noted that in this specification, "stabilizer solution" means, for example, that the elements (atoms) contained in the stabilizer are dissolved in zirconium oxide.

[0194] Regarding the stabilizer in the zirconia pre-calcined body of the present invention, examples can be made of stabilizers similar to those in the zirconia composition, from those related to the monoclinic crystal ratio f. m From the viewpoint that the zirconia sintered body exhibits excellent light transmittance regardless of whether it is sintered normally or for a short time, yttrium oxide is preferred. The stabilizer content in the zirconia pre-sintered body of the present invention is the same as that in the zirconia composition, for example, preferably 2 to 9 mol% relative to the total molar number of zirconia and stabilizer, more preferably 3 to 8 mol%.

[0195] Solid solution occurs irreversibly using energy from an external source. For monoclinic crystal ratio f... m In general, the larger r1 is, the smaller r2 is, the higher the yttrium oxide content, or the higher the pre-calcination temperature (described later), the more likely solid solution treatment will be performed, based on the solid solution f. m reduce.

[0196] Furthermore, solid solution is not limited to the heat energy based on pre-calcination. Through processes such as mixing zirconium oxide particles and stabilizer particles (described later), simultaneously crushing the individual particles, and / or drying, the monoclinic crystal ratio f can be increased. m The price decreases due to solid solution treatment.

[0197] In zirconia pre-sintered bodies made solely from zirconia particles with a stabilizer dissolved in solid solution, the monoclinic crystallinity f m Less than 10%, therefore, as the zirconia pre-burnt body of the present invention, at least a portion of the stabilizer needs to be non-soluble in zirconia.

[0198] The content of the stabilizer in the zirconia pre-sintered body of the present invention can be determined, for example, by inductively coupled plasma (ICP) luminescence spectrophotometry or fluorescence X-ray analysis. In the zirconia pre-sintered body of the present invention, the content of the stabilizer (suitably yttrium oxide) relative to the total molar percentage of zirconia and stabilizer is preferably 2.0 to 9.0 mol%, more preferably 3.0 to 8.0 mol%.

[0199] If the stabilizer content is less than 2.0 mol%, the light transmittance of the zirconia sintered body will be insufficient. If it exceeds 9.0 mol%, the monoclinic crystal ratio f in the zirconia pre-sintered body will be insufficient. m The light transmittance is reduced due to the crystalline structure, therefore it is not preferred.

[0200] The zirconia pre-sintered body of the present invention, with the stabilizer partially dispersed, moderately reduces the regularity of the sintered structure, resulting in a sintered body with high light transmittance and low opalescence, and is therefore preferred. In this invention, "partial" refers to a range of an equivalent circle with a diameter of approximately 10 nm. If both the stabilizer and zirconia are present within this range, the crystalline structure after sintering remains small, and the light transmittance is improved, thus making it preferred.

[0201] When the composition of the zirconia pre-sintered body of the present invention is locally measured, elements other than oxygen atoms (e.g., yttrium) of the oxide constituting the stabilizer are detected within the particles of the stabilizer. For example, when the stabilizer contained in the zirconia pre-sintered body of the present invention is yttrium oxide, yttrium is detected within the particles of yttrium oxide when the composition of the particles of yttrium oxide is locally measured. The particles of yttrium oxide are mostly composed of yttrium oxide, but also contain trace amounts of zirconia and other elements besides yttrium oxide. When observing the compositional distribution of the zirconia pre-sintered body, the local content (amount) of elements other than oxygen atoms (e.g., yttrium) of the oxide of the stabilizer constituting the particles of the stabilizer (suitably particles of yttrium oxide) is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more. When the presence of the aforementioned elements is less than 10 mol%, it indicates that zirconium oxide and the stabilizer are almost completely dissolved, and the sintered body contains almost no particles larger than 100 nm (i.e., it becomes a regular crystalline structure), resulting in high opalescence, which is therefore not preferred. Furthermore, the local content of elements other than oxygen atoms in the oxide constituting the aforementioned stabilizer is preferably 90 mol% or less, more preferably 85 mol% or less, and even more preferably 80 mol% or less. When it is more than 90 mol%, it indicates that the solid solution of zirconium oxide and the stabilizer has almost not occurred. During sintering, the area with less stabilizer on the outside of the stabilizer particles increases, the amount of diffusion increases, and the diffusion distance becomes longer. Therefore, for the crystalline structure after sintering, the number of particles larger than 100 nm is excessively increased, and the light transmittance ΔL1 and L2 decreases, which is therefore not preferred. The local content of the aforementioned elements can be any combination of these values. For example, it is preferably 10 to 90 mol%, more preferably 15 to 85 mol%, and even more preferably 20 to 80 mol%. By using a concentration of 10–90 mol%, sintered zirconia bodies with high light transmittance and low opalescence after sintering can be obtained, making it a preferred option.

[0202] The local elemental composition of the zirconia pre-calcined body of the present invention can be confirmed, for example, by using an electron microscope such as a transmission electron microscope or a scanning electron microscope. Conditions can be determined such that the spatial resolution of the electron microscope is, for example, smaller than the average primary particle size of the composition. Examples of such conditions include setting the electron microscope's analysis mode to point analysis mode and setting the accelerating voltage to a low level (e.g., below 100 kV, below 10 kV, etc.). This reduces the range of electron beam diffusion within the sample, reduces the area where characteristic X-rays proportional to the elemental mass are generated, and allows for more accurate measurement. Another example is analyzing near the center of gravity of the particles rather than at the outer periphery. Furthermore, another example is using an energy-dispersive X-ray analyzer or a wavelength-dispersive X-ray analyzer in the detector. For example, by using a wavelength-dispersive detector, more accurate measurement is possible.

[0203] The local elemental composition of the zirconia pre-fired body of the present invention is affected by the degree of solid solubility of zirconia in the stabilizer. For example, the smaller the primary particle size of the stabilizer contained in the composition, the easier it is for the stabilizer to solidify in zirconia; the larger the primary particle size, the more difficult it is for zirconia to solidify. Therefore, the particle size range of the aforementioned zirconia composition is preferred. In addition, the solid solubility of zirconia in the stabilizer can also be achieved through mixing and pulverizing processes, degreasing, or energy during pre-firing, resulting in material diffusion. Therefore, a suitable manufacturing method is preferred.

[0204] Regarding opalescence, for the 1.2 mm thick sintered body of the zirconia pre-sintered body of the present invention after sintering at 900–1400 °C for 120 minutes, from the viewpoint of the appearance of dental materials, the OP value calculated using the following mathematical formula (2) is preferably less than 15, more preferably less than 10, and even more preferably less than 7. When it is 15 or higher, it may appear to have a specific color. The opalescence of the aforementioned 1.2 mm thick sintered body may also refer to the value after sintering at 1300 °C for 120 minutes.

[0205] Opalescence refers to the OP value calculated using the following mathematical formula (2) by measuring the transmitted and reflected light using an F11 light source of a spectrophotometer (manufactured by KONICA MINOLTA JAPAN Co., Ltd., "CM-3610A").

[0206]

Mathematical Expression 3

[0207]

[0208] (where a) ＊ 透射 and b ＊ 透射 L*a*b* represents the color coordinates of the color system in transmitted light, where a＊ 反射 and b ＊ 反射 The L*a*b* color coordinates represent the color system in the reflected light.

[0209] For the zirconia pre-sintered body of the present invention, from the viewpoint of sufficient aesthetics of dental materials, the ΔL*(WB) of the sintered body with a thickness of 1.2 mm after sintering at 900-1400°C for 120 minutes is preferably 5 or more. When it is less than 5, the white is too strong, and sufficient transparency may not be obtained. ΔL*(WB) refers to the difference between the lightness (L*) on a white background and the lightness (L*) on a black background. Specifically, it refers to the difference between the L* value on a white background and the L* value on a black background of the 1.2 mm thick zirconia sintered body. The L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z8781-4:2013). The white background refers to the white portion of the opacity test paper described in Section 1, Part 4 of JIS K 5600-4-1:1999, and the black background refers to the black portion of the aforementioned opacity test paper. ΔL*(WB) can be measured using, for example, an F11 light source from a spectrophotometer (manufactured by KONICA MINOLTA JAPAN Co., Ltd., “CM-3610A”).

[0210] The first translucency ΔL1*(WB) of the first sintered body prepared by sintering at 1300°C for 120 minutes and the second translucency ΔL2*(WB) of the second sintered body prepared by sintering at 1300°C for 10 minutes satisfy the relationship of the following mathematical formula (3). Within this range, even with a shortened sintering time for preparing the sintered body, sufficient aesthetics of the dental material can be maintained. The first and second translucency are described in the "Determination of ΔL*(WB) of Zirconia Sintered Body" of the embodiments described later.

[0211] ΔL2* (WB) / ΔL1* (WB)≥0.85 (3)

[0212] For the zirconia pre-sintered body of the present invention, in the sintered body after sintering at 900–1400°C for 120 minutes, the particle size distribution based on the number of peaks has at least one peak in the range of particle size (crystal size) of 70 nm or more and 100 nm or less. This is preferred from the viewpoint of not reducing the light transmittance ΔL*(WB). As some suitable embodiments, from the viewpoint of reducing the regularity of the crystalline structure after sintering and reducing opalescence, a zirconia pre-sintered body with two or more peaks in the particle size distribution based on the number of peaks can be cited. For example, a zirconia pre-sintered body with two peaks in the above-mentioned particle size distribution based on the number of peaks after sintering can be cited, wherein the first peak (hereinafter also referred to as "first peak") is in the range of particle size (crystal size) of 70 nm or more and 100 nm or less, and the second peak is in the range of particle size exceeding 100 nm. The particle size distribution based on the number of peaks can be evaluated by the method described in the "Determination of Crystallographic Grain Size Distribution in Zirconia Sintered Body" of the embodiments described later. In this specification, "crystal grain size" refers to the grain size of a particle determined by the method described in the "Determination of Crystal Grain Size Distribution in Zirconia Sintered Body" example described later.

[0213] For the zirconia pre-sintered body of the present invention, in the sintered body after sintering at 900–1400°C for 120 minutes, the proportion of particles with a diameter greater than 100 nm in the particle size distribution (based on the number of particles) is preferably 3% or more, more preferably 5% or more. By setting it to 3% or more, the OP value can be reduced. In addition, the proportion of particles with a diameter greater than 100 nm is preferably 15% or less, more preferably 12% or less. When it is greater than 15%, the light transmittance may be reduced. It can also be set to any combination of these ranges. The proportion of particles with a diameter greater than 100 nm is preferably, for example, 3–15%, more preferably 5–12%. The method for measuring the crystal grain size in the sintered body after sintering at 900–1400°C is as described in the "Determination of Crystal Grain Size Distribution in Zirconia Sintered Body" of the embodiments described later.

[0214] As a suitable implementation, in addition to any of the above-described components (e.g., a zirconia pre-sintered body containing zirconia and a stabilizer capable of suppressing the phase transformation of zirconia, wherein at least a portion of the stabilizer is not dissolved in zirconia, and the monoclinic crystal ratio f shown in formula (1) is... m In addition to 50-98% (the local presence of stabilizer in the particles derived from stabilizer is 10-90 mol%), zirconia pre-sintered bodies can be cited as an example. In the sintered body after sintering at 900-1400°C for 120 minutes, the particle size distribution based on the number of particles has at least one peak in the range of particle size above 70 nm and below 100 nm, and contains 3-15% of particles with a particle size greater than 100 nm.

[0215] [Manufacturing method of zirconia pre-sintered body]

[0216] As another embodiment of the present invention, a method for manufacturing a zirconia pre-fired body using the aforementioned zirconia composition can be cited. Specifically, a method for manufacturing a zirconia pre-fired body having a step of calcining (pre-firing) the aforementioned zirconia composition at 200 to 900°C can be cited. The zirconia pre-fired body is obtained, for example, by calcining (pre-firing) the aforementioned zirconia composition at 200 to 900°C to remove organic matter, dissolving a desired amount of stabilizer in the zirconia, and performing a primary particle necking.

[0217] The pre-firing temperature for manufacturing the zirconia pre-fired 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 it to 200°C or higher, organic matter can be removed, and adverse effects in subsequent sintering processes can be easily avoided. Furthermore, it is preferably 900°C or lower, more preferably 700°C or lower, and even more preferably 600°C or lower. By setting the pre-firing temperature to 900°C or lower, the monoclinic crystal ratio f caused by solid solution can be suppressed. m The reduction in light transmittance allows for excellent light transmittance in a short time during subsequent sintering processes. The pre-firing temperature can be set to any combination of these parameters within a range. A preferred pre-firing temperature is, for example, 200–900°C, more preferably 300–700°C, and even more preferably 400–600°C.

[0218] The pre-firing time for manufacturing the zirconia pre-fired body of the present invention is preferably 30 minutes or more, more preferably 120 minutes or more. Setting it to 120 minutes or more is preferable in terms of removing organic matter and not adversely affecting subsequent sintering processes. Furthermore, the pre-firing time is preferably 360 minutes or less, more preferably 240 minutes or less. Setting it to 240 minutes or less suppresses the monoclinic crystal ratio f caused by solid solution. m The reduction in light transmittance and the diffusion distance of the stabilizer result in excellent light transmittance in a short time during the subsequent sintering process, which is preferable from this perspective. The pre-firing time can also be set to any combination of these parameters within a range. For example, the pre-firing time is preferably 30 to 360 minutes, and more preferably 120 to 240 minutes.

[0219] [Zirconium oxide sintered body]

[0220] Next, the zirconia sintered body of the present invention will be described.

[0221] The zirconia sintered body of the present invention can be manufactured using the aforementioned zirconia composition or zirconia pre-sintered body. Specifically, the zirconia sintered body of the present invention is obtained, for example, by sintering the aforementioned zirconia composition or zirconia pre-sintered body. A zirconia sintered body refers to a substance in a fully sintered state.

[0222] The zirconia sintered body of the present invention comprises zirconia and a stabilizer capable of suppressing the phase transformation of zirconia. The stabilizer content is 2 to 9 mol% relative to the total molar percentage of zirconia and the stabilizer. Regarding the stabilizer in the zirconia sintered body of the present invention, the same stabilizer as that in the zirconia composition can be cited. From the viewpoint of excellent light transmittance, yttrium oxide is preferred. As some suitable embodiments, a zirconia sintered body is provided in which the yttrium oxide content is 2-9 mol% relative to the total molar percentage of zirconia and the stabilizer. The stabilizer (suitably yttrium oxide) content in the zirconia sintered body of the present invention is the same as that in the zirconia composition, for example, preferably 2-9 mol% relative to the total molar percentage of zirconia and the stabilizer, more preferably 3-8 mol%. From the viewpoint of obtaining sufficient light transmittance, the yttrium oxide content is preferably 2-9 mol%. Furthermore, since the yttrium oxide content is 9 mol% or less, it has sufficient mechanical strength. From the perspective of obtaining zirconia sintered bodies with superior light transmittance and mechanical strength, the yttrium oxide content in the zirconia sintered body is preferably 3.0 mol% or more, more preferably 4.0 mol% or more, and further preferably 8.0 mol% or less, more preferably 7.0 mol% or less. The yttrium oxide content can be determined by, for example, inductively coupled plasma (ICP) luminescence spectrophotometry or fluorescence X-ray analysis.

[0223] For the zirconia sintered body of the present invention, the ΔL*(WB) in a sintered body with a thickness of 1.2 mm is 5 or more. If it is less than 5, the white color is too strong, and sufficient transparency cannot be obtained. From the viewpoint of achieving sufficient aesthetics in dental materials, a value of 5 or more is preferred. The method for measuring ΔL*(WB) in the zirconia sintered body is as described in the examples described later.

[0224] For the zirconia sintered body of the present invention, the OP value calculated by the above mathematical formula (2) for a sintered body with a thickness of 1.2 mm is less than 15. When it is 15 or more, it appears to have a particular color, which is not preferred. From the viewpoint of the appearance of dental materials, it is preferred to be 10 or less, and more preferably 7 or less. The OP value can be calculated by measuring the transmitted light and reflected light using the F11 light source of a spectrophotometer (manufactured by KONICAMINOLTA JAPAN Co., Ltd., "CM-3610A"), for example, using the above mathematical formula (2).

[0225] Zirconia sintered bodies generally possess optical properties such as light transmittance and opalescence. In the zirconia sintered body of the present invention, light transmittance is improved when the crystal grain size is smaller than the wavelength of the visible light region. Furthermore, due to reduced scattering, the transmittance of linear light is also increased. On the other hand, when the crystal grain size is only smaller than the visible light region, opalescence originating from the structure occurs, giving the appearance of color and degrading its appearance. The crystal grain size of the sintered body of the present invention refers to the grain size of the internal crystalline structure of the zirconia sintered body.

[0226] From the viewpoint of not reducing light transmittance ΔL*(WB), the zirconia sintered body of the present invention preferably has at least one peak in a particle size distribution based on the number of particles in the range of 70 nm or more and 100 nm or less.

[0227] As some suitable embodiments, zirconia sintered bodies can be cited where, regarding the peaks in the aforementioned range of the sintered body, from the perspective of reduced regularity of the crystalline structure and reduced opalescence, there are two or more peaks in the aforementioned range in the particle size distribution based on the number of peaks. For example, a zirconia sintered body with two peaks in the aforementioned range (bimodal) can be cited. The particle size distribution based on the number of peaks can be evaluated by the method described in the "Determination of Crystalline Grain Size Distribution in Zirconia Sintered Bodies" of the embodiments described later.

[0228] From the viewpoint of improving ΔL*(WB), the average crystal grain size of the zirconia sintered body of the present invention is preferably 100 nm or less.

[0229] In this specification, "average crystal grain size" refers to the arithmetic mean diameter of the grain size distribution based on the number of grains, as determined by the method described in the "Determination of Crystal Grain Size Distribution in Zirconia Sintered Body" example described later.

[0230] Furthermore, from the viewpoint of suppressing opalescence, in the distribution of crystal grain size (particle size distribution based on the number of particles), the proportion of particles with a grain size (crystal grain size) exceeding 100 nm is preferably 3% or more, more preferably 5% or more. By setting the above proportion to 3% or more, the OP value can be reduced. Moreover, the proportion of particles with a grain size exceeding 100 nm is preferably 15% or less, more preferably 12% or less. When the aforementioned proportion is higher than 15%, light transmittance may be reduced. Any combination of these ranges can also be used. For the crystal grain size distribution of the zirconia sintered body, the proportion of particles with a grain size exceeding 100 nm is preferably, for example, 3 to 15%, more preferably 5 to 12%.

[0231] The zirconia sintered body of the present invention may contain a fluorescent agent. The zirconia sintered body exhibits fluorescence by containing the fluorescent agent. There is no particular limitation on the type of fluorescent agent; one or more substances capable of emitting fluorescence at any wavelength can be used. Examples of such fluorescent agents include those containing a metal element. Examples of such metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain only one of these metal elements or may contain two or more. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred from the perspective of more significantly achieving the effects of the present invention, and Bi and Eu are more preferred. Examples of fluorescent agents used in manufacturing the zirconia sintered body of the present invention include oxides, hydroxides, acetates, and nitrates of the aforementioned metal elements.

[0232] Alternatively, fluorescent agents can be Y₂SiO₅:Ce, Y₂SiO₅:Tb, (Y,Gd,Eu)BO₃, Y₂O₃:Eu, YAG:Ce, ZnGa₂O₄:Zn, BaMgAl 10 O 17 Eu et al.

[0233] The content of fluorescent agent in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of fluorescent agent or the intended use of the zirconia sintered body. From the viewpoint of preferably using it as a dental restoration, the content of the fluorescent agent, calculated based on the oxides of the metal elements contained in the fluorescent agent 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 fluorescent agent, calculated based on the oxides of the metal elements contained in the fluorescent agent, is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. By making this content above the lower limit, the fluorescence is not inferior even compared to natural human teeth. Furthermore, by making this content below the upper limit, the reduction in translucency and mechanical strength can be suppressed.

[0234] The zirconia sintered body of the present invention may also contain a colorant. The zirconia sintered body becomes a colored zirconia sintered body by containing a colorant. There are no particular limitations on the type of colorant; known pigments commonly used for coloring ceramics, known dental liquid colorants, etc., can be used. Examples of colorants include colorants containing metallic elements, specifically oxides, composite oxides, or salts of metallic elements such as iron, vanadium, praseodymium, erbium, chromium, nickel, and manganese. Alternatively, commercially available colorants can be used, such as Prettau Colour Liquid manufactured by Zirkonzahn Corporation. The zirconia sintered body may contain one colorant or two or more colorants.

[0235] The content of colorant in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of colorant and the intended use of the zirconia sintered body. However, from the viewpoint of being preferably used as a dental restoration, the 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, relative to 100% by mass of zirconia contained in the zirconia sintered body, calculated as oxides of the metal elements contained in the colorant. Furthermore, the content of colorant, calculated as oxides of the metal elements 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 also be 0.1% by mass or less, and further may be 0.05% by mass or less.

[0236] According to the present invention, a zirconia sintered body with excellent linear light transmittance can be obtained. To adjust the light transmittance of this zirconia sintered body, the zirconia sintered body of the present invention may also contain a light transmittance modifier. Specific examples of light transmittance modifiers include alumina, titanium dioxide, silicon dioxide, zircon, lithium silicate, and lithium disilicate. The zirconia sintered body may contain one type of light transmittance modifier or two or more types of light transmittance modifiers.

[0237] There is no particular limitation on the content of the light transmittance modifier in the zirconia sintered body. It can be appropriately adjusted according to the type of light transmittance modifier and the intended use of the zirconia sintered body. However, from the viewpoint of preferably using it as a dental patch, it is preferably 0.1% by mass or less relative to 100% by mass of zirconia contained in the zirconia sintered body.

[0238] [Method for manufacturing zirconia sintered bodies]

[0239] The method for manufacturing the zirconia sintered body of the present invention can be exemplified by a method using the zirconia composition of the present invention (e.g., a shaped body). Preferably, the method for manufacturing the zirconia sintered body is a method that includes a step of sintering the zirconia composition at atmospheric pressure and at 900–1400°C.

[0240] In addition, as another embodiment, a method for manufacturing a zirconia sintered body using the zirconia pre-sintered body of the present invention can be cited. Preferably, it is a manufacturing method that includes the step of sintering the zirconia pre-sintered body at 900 to 1400°C under normal pressure.

[0241] The aforementioned manufacturing method allows for the easy production of the zirconia sintered body of the present invention, which possesses excellent mechanical strength, light transmittance, and linear light transmittance.

[0242] The zirconia sintered body of the present invention can be manufactured by sintering the zirconia composition of the present invention under normal pressure. Alternatively, it can be manufactured by sintering the zirconia pre-sintered body of the present invention under normal pressure.

[0243] In both cases of sintering the zirconia composition (e.g., a shaped body) of the present invention to produce a sintered body and sintering the zirconia pre-sintered body of the present invention to produce a sintered body, it is preferable to have a sinterable temperature (e.g., a maximum sintering temperature) that maximizes the light transmittance and minimizes the opalescence of the zirconia sintered body. From the viewpoint of easily obtaining the target zirconia sintered body under normal pressure, the sinterable temperature is preferably 900°C or higher, more preferably 1000°C or higher, even more preferably 1050°C or higher, and preferably 1400°C or lower, more preferably 1350°C or lower, and even more preferably 1300°C or lower. By setting the sinterable temperature to the lower limit or above, sintering can be carried out sufficiently, and a dense sintered body can be easily obtained. In addition, by setting the sinterable temperature to the upper limit or below, a zirconia sintered body with a crystal grain size within the suitable range of the present invention can be easily obtained, and the deactivation of the fluorescent agent can be suppressed.

[0244] In either the case of sintering the zirconia composition (e.g., a shaped body) of the present invention to produce a sintered body, or the case of sintering the zirconia pre-sintered body of the present invention to produce a sintered body, there is no particular limitation on the sintering time. However, from the perspective of being able to obtain the target zirconia sintered body with good productivity and efficiency, the holding time at the sinterable temperature (e.g., the highest sintering temperature) is preferably less than 120 minutes, more preferably 90 minutes or less, further 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. This holding time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more.

[0245] In both cases of sintering the zirconia composition (e.g., a shaped body) of the present invention to manufacture a sintered body and sintering the zirconia pre-sintered body of the present invention to manufacture a sintered body, the sintering time for manufacturing the sintered body can be shortened without reducing the light transmittance and strength of the manufactured zirconia sintered body. In particular, the holding time at the highest sintering temperature for manufacturing the sintered body can be shortened (short-time sintering). This improves production efficiency; when the zirconia pre-sintered body of the present invention is applied to dental products, the dimensions of the dental product for treatment can be determined, the time from machining to the point where the dental product can be used for treatment can be shortened, and the time burden on patients can be reduced. Furthermore, energy costs can be reduced.

[0246] In the sintering process, the holding time at the sinterable temperature (e.g., the highest sintering temperature) can also be set to less than 25 minutes, less than 20 minutes, or less than 15 minutes.

[0247] The heating and cooling rates in the sintering process are preferably set to shorten the sintering time. For example, the heating rate can be set according to the performance of the calcining furnace to reach the maximum sintering temperature in the shortest possible time. The heating rate up to reaching the maximum sintering temperature can be set to, 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 cooling rate is preferably set to a rate that prevents defects such as cracks from forming in the sintered body. For example, the sintered body can be cooled to room temperature after heating is completed.

[0248] The sintering in this invention can be carried out using a sintering furnace. There are no particular limitations on the type of sintering furnace; for example, electric furnaces and degreasing furnaces commonly used in industry can be used. Especially in the case of use in dental materials, in addition to conventional dental zirconia sintering furnaces, dental porcelain furnaces with relatively low sintering temperatures (e.g., maximum sintering temperatures) can also be used.

[0249] The zirconia sintered body of the present invention possesses both high light transmittance and low opalescence. Furthermore, considering the excellent light transmittance even during short sintering times, the first light transmittance ΔL1*(WB) of the first sintered body prepared by sintering at 1300°C for 120 minutes and the second light transmittance ΔL2*(WB) of the second sintered body prepared by sintering at 1300°C for 10 minutes preferably satisfy the relationship of the following formula (3). The first and second light transmittances are described in the "Determination of ΔL*(WB) of Zirconia Sintered Body" of the embodiments described later.

[0250] ΔL2* (WB) / ΔL1* (WB)≥0.85 (3)

[0251] The zirconia sintered body of the present invention can be easily manufactured even without HIP treatment, but by performing HIP treatment after sintering under the above-mentioned atmospheric pressure, the light transmittance and mechanical strength can be further improved.

[0252] Applications of zirconia sintered bodies

[0253] There are no particular limitations on the use of the zirconia sintered body of the present invention.

[0254] Zirconia sintered bodies are particularly suitable as dental materials, such as dental restorations, due to their excellent light transmittance and linear light transmittance. They are especially useful not only as dental restorations for the cervical region of teeth but also as restorations for the occlusal surfaces of molars and the incisal edges of anterior teeth. The zirconia sintered body of the present invention is particularly preferred for use as a dental restoration for the incisal edges of anterior teeth.

[0255] Example

[0256] The present invention will now be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples, etc. It should be noted that the measurement methods are as described below.

[0257] <Method for determining the average primary particle size of zirconium oxide and stabilizer in zirconium oxide compositions>

[0258] The zirconium oxide particles and / or stabilizer particles were photographed using a transmission electron microscope (TEM). In the obtained image, for any 100 particles, the equivalent circle diameter (the diameter of a complete circle with the same area) was calculated using the following formula based on the area of ​​each particle. The average value of the equivalent circle diameter of the 100 particles was taken as the average primary particle size.

[0259] R = 2(S / π) (1 / 2)

[0260] (In the formula, S represents the area of ​​the particle, and R represents the particle size (diameter).)

[0261] <Content of stabilizer in zirconium oxide composition (mol%)>

[0262] The content (mol%) of stabilizer in the zirconium oxide composition was determined using a fluorescence X-ray analysis (XRF) device (RX3000, manufactured by Matsusada Precision Co., Ltd.) as the content of stabilizer relative to the total moles of zirconium oxide and stabilizer.

[0263] <Method for determining the full width at half maximum (FWHM) of the peaks derived from stabilizers in zirconium oxide compositions>

[0264] The half-peak width (WHM) of the stabilizer peaks in the zirconium oxide composition derived from the present invention was determined using a powder obtained by drying the zirconium oxide composition at room temperature as a sample. For this sample, the WHM was determined for the peaks around 29° using a fully automated horizontal multi-object X-ray diffractometer (SmartLab, Rigaku Corporation) and X-ray analysis integration software (SmartLab Studio II, Rigaku Corporation) under the following conditions.

[0265] X-ray source:

[0266] Goniometer length: 300mm

[0267] Optical system: lumped method

[0268] Detector: High-speed one-dimensional X-ray detector (D / teX Ultra250)

[0269] Monochromaticization: Kβ filter

[0270] Tube voltage: 40kV

[0271] Tube current: 30mA

[0272] Scan axis: 2θ / θ

[0273] Scanning speed: 0.2° / minute

[0274] Sampling step size: 0.01°

[0275] < Monoclinic crystallinity f of zirconia pre-sintered body m The determination of >

[0276] The monoclinic crystal ratio f of the present invention m It is determined by analyzing the crystalline phase in the pre-burned body. Specifically, X-ray diffraction (XRD) is performed, and the result is obtained using the following formula.

[0277] f m =I 28 / (I 28 +I 30 )*100 (1)

[0278] (where f) m The percentage (%) of the monoclinic crystal system is represented in XRD measurements. 28 I represents the area intensity of the peak near 2θ = 28° where the main peak appears in the monoclinic crystal system. 30 This represents the area intensity of the peak near 2θ = 30° where the main peak appears in the tetragonal or cubic crystal system.

[0279] In the measurements, the disc-shaped zirconia pre-fired bodies of each embodiment and comparative example were used as samples.

[0280] <Method for determining the compositional distribution of zirconia pre-sintered bodies>

[0281] The compositional distribution of the zirconia preheater was determined using a field emission scanning electron microscope (FE-SEM Reglus 8220, manufactured by Hitachi HIGHTEC Co., Ltd.) and an energy-dispersive X-ray analyzer (Aztec Energy X-Max 50, manufactured by 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-derived particles was calculated.

[0282] Magnification ratio: 20,000 times

[0283] Analysis Mode: Point Analysis

[0284] Accelerating voltage: 5kV

[0285] Working distance: 15mm±1mm

[0286] X-ray extraction angle: 30 degrees

[0287] Dead time: 7%

[0288] Measurement time: 100 seconds

[0289] <Determination of ΔL*(WB) of zirconia sintered body>

[0290] ΔL*(WB) of zirconia sintered bodies was measured using a spectrophotometer (KONICA MINOLTA JAPAN Co., Ltd., "CM-3610A"). ΔL*(WB) represents the difference in lightness (L*) against a white background and lightness (L*) against 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 Part 4, Section 1 of JIS K5600-4-1:1999, and the black background refers to the black portion of the aforementioned opacity test paper. In this measurement, an F11 light source was used, and the value was determined by measuring the reflected light. A disc-shaped zirconia sintered body with a diameter of 16 mm and a thickness of 1.2 mm, obtained through mirror polishing, was used as the sample.

[0291] For the zirconia sintered bodies of the aforementioned samples, two zirconia sintered bodies were prepared: one obtained by holding the zirconia at the highest sintering temperature of 1300℃ for 120 minutes (sintering for 120 minutes) (first sintered body) and the other obtained by holding the zirconia at the highest sintering temperature of 1300℃ for 10 minutes (sintering for 10 minutes) (second sintered body). The average values ​​measured with n=3 were calculated for each.

[0292] The first translucency ΔL1*(WB) of the first sintered body prepared by sintering at 1300℃ for 120 minutes and the second translucency ΔL2*(WB) of the second sintered body prepared by sintering at 1300℃ for 10 minutes were determined, and the relationship between the first translucency ΔL1*(WB) and the second translucency ΔL2*(WB) was evaluated.

[0293] It should be noted that for Comparative Examples 1, 2, 5 and 6, except that the maximum sintering temperature was changed as described in Table 2, ΔL*(WB) was measured as a transmittance, as described above.

[0294] <Opaqueness of Zirconia Sintered Bodies>

[0295] In the evaluation of the opalescence of zirconia sintered bodies, a disc-shaped zirconia sintered body with a diameter of 16 mm and a thickness of 1.2 mm, which was used in the above-mentioned ΔL*(WB) determination, was used as the sample.

[0296] To assess the opalescence of the zirconia sintered body, the transmitted and reflected light were measured using an F11 light source of a spectrophotometer (KONICA MINOLTA JAPAN Co., Ltd., “CM-3610A”), and the OP value was calculated using the following mathematical formula (2).

[0297]

Mathematical Expression 4

[0298]

[0299] (where a) ＊ 透射 and b ＊ 透射 L*a*b* represents the color coordinates of the color system in transmitted light, where a ＊ 反射 and b ＊ 反射 The L*a*b* color coordinates represent the color system in the reflected light.

[0300] From the viewpoint of the appearance of dental materials, the OP value is preferably less than 15, more preferably less than 10, and even more preferably less than 7.

[0301] <Measurement of grain size and calculation of grain size distribution in zirconia sintered bodies>

[0302] For the zirconia pre-sintered bodies obtained in the following examples or comparative examples, surface images were obtained using a scanning electron microscope (trade name "VE-9800", manufactured by KEYENCE Co., Ltd.). For the obtained images, the grain boundaries of each grain were recorded, and the crystal grain size of each grain was measured by image analysis. The crystal grain size was measured using image analysis software (trade name "Image-Pro Plus", manufactured by Hakuto Co., Ltd.). The imported SEM image was binarized, and the brightness range was adjusted to make the grain boundaries clear, allowing particles to be identified from the field of view (area). The crystal grain size obtained by Image-Pro Plus refers to the diameter passing through the centroid of the particle. The crystal grain size is defined as the length of a line segment obtained by connecting the contour lines obtained from the grain contour lines, measured with the centroid as the center and averaged at a 2-degree scale. In the SEM images (10 fields of view) of each example and comparative example, the crystal grain size was measured for all grains not appearing at the edge of the image.

[0303] By graphically representing the relationship between the crystal size of each particle and the number of crystals, a particle size distribution (a particle size distribution based on the number of crystals) was created.

[0304] It should be noted that by graphically representing the relationship between the size (area) of the crystals obtained from each grain and the number of crystals, it is also possible to create... Figure 5 The crystallization chart shown is an area distribution based on the number of crystals.

[0305] It should be noted that "particles not appearing at the image edge" refers to particles within the SEM image frame that are excluded from the frame, excluding particles whose outlines are not fully incorporated (particles whose outlines are interrupted at the top, bottom, left, and right boundaries). The crystal size of all particles not attached to the image edge can be determined in Image-Pro Plus by selecting the option to exclude all particles on the boundary lines.

[0306] <Determination of linear light transmittance>

[0307] The linear light transmittance of a 1.0 mm thick zirconia sintered body was determined as follows: A turbidimeter (Nippon Denshoku Kogyo Co., Ltd., "Haze Meter NDH 4000") was used to measure the transmission and scattering of light emitted from a light source onto the sample, and an integrating sphere was employed for measurement. In this measurement, linear light transmittance was determined according to ISO 13468-1:1996 and JIS K 7361-1:1997, and haze was determined according to ISO 14782-1:1999 and JIS K 7136:2000. A disc-shaped zirconia sintered body with a diameter of 16 mm and a thickness of 1.0 mm, obtained by mirror polishing on both sides, was used as the sample.

[0308] [Manufacturing Example 1] (Zirconium oxide particles with an average primary particle size r1 of 35 nm)

[0309] Prepare 1.0 L of a 0.62 mol / L zirconium oxychloride aqueous solution and 0.5 L of a 1.9 mol / L sodium hydroxide aqueous solution, respectively.

[0310] 1.0L of pure water is injected into the sedimentation tank, followed by the injection of the above-mentioned zirconium oxychloride aqueous solution and sodium hydroxide aqueous solution, so that zirconium oxychloride precipitates to obtain a slurry.

[0311] After filtration and washing, 22.2 g of acetic acid was added to the slurry, and the mixture was subjected to hydrothermal treatment at 200°C for 2 hours. The resulting slurry was then centrifuged and filtered using a membrane filter with a pore size of 100 nm to obtain a zirconia slurry with coarse particles removed. The average primary particle size of the zirconia particles was 35 nm. The slurry was then concentrated using an evaporator to obtain an aqueous slurry containing 20% ​​by mass of zirconia particles.

[0312] [Manufacturing Example 2] (Zirconium oxide particles with an average primary particle size r1 of 50 nm)

[0313] The slurry from Manufacturing Example 1 was placed in a centrifuge tube and processed at 3000 rpm for 5 minutes. The upper part of the slurry in the centrifuge tube was removed to obtain a zirconia slurry. The zirconia slurry contained zirconia particles with an average primary particle size of 50 nm. It was concentrated using an evaporator to obtain an aqueous slurry containing 20% ​​by mass of zirconia particles.

[0314] [Manufacturing Example 3] (Zirconium oxide particles with an average primary particle size r1 of 10 nm)

[0315] The slurry from Preparation Example 1 was placed in a centrifuge tube and processed at 3000 rpm for 5 minutes. The supernatant was removed by decantation to obtain a zirconia slurry. The zirconia slurry contained zirconia particles with an average primary particle size of 10 nm. It was concentrated using an evaporator to obtain an aqueous slurry containing 20% ​​by mass of zirconia particles.

[0316] [Manufacturing Example 4] (Yttrium oxide particles with an average primary particle size r2 of 20 nm)

[0317] 3 kg of yttrium oxide was mixed with 7 kg of water and pulverized using a bead mill to obtain an aqueous slurry containing dispersed yttrium oxide. The resulting slurry was centrifuged and filtered through a membrane filter with a pore size of 100 nm to obtain a yttrium oxide slurry with coarse particles removed. The average primary particle size of the yttrium oxide particles in this slurry was 20 nm. This slurry was then concentrated using an evaporator to obtain an aqueous slurry containing 20% ​​by mass of yttrium oxide particles.

[0318] [Manufacturing Example 5] (Yttrium oxide particles with an average primary particle size r2 of 50 nm)

[0319] The slurry from Preparation Example 4 was placed in a centrifuge tube and processed at 3000 rpm for 5 minutes. The upper part of the slurry in the centrifuge tube was removed to obtain a yttrium oxide slurry. The average primary particle size of the yttrium oxide particles contained in this yttrium oxide slurry was 50 nm. It was concentrated using an evaporator to obtain an aqueous slurry containing 20% ​​by mass of yttrium oxide particles.

[0320] [Manufacturing Example 6] (Yttrium oxide particles with an average primary particle size r2 of 10 nm)

[0321] The slurry from Preparation Example 4 was placed in a centrifuge tube and processed at 3000 rpm for 5 minutes. The supernatant was removed by decantation to obtain a yttrium oxide slurry. The average primary particle size of the yttrium oxide particles contained in this yttrium oxide slurry was 10 nm. It was concentrated using an evaporator to obtain an aqueous slurry containing 20% ​​by mass of yttrium oxide particles.

[0322] [Manufacturing Example 7] (Zirconium oxide particles with an average primary particle size r1 of 100 nm)

[0323] Add 7 kg of water to 3 kg of zirconium oxide and pulverize using a bead mill to obtain an aqueous slurry containing dispersed zirconium oxide. The average primary particle size of the zirconium oxide particles in the slurry is 100 nm. Concentrate the slurry using an evaporator to obtain an aqueous slurry containing 20% ​​by mass of zirconium oxide particles.

[0324] [Manufacturing Example 8] (Yttrium oxide particles with an average primary particle size r2 of 100 nm)

[0325] Add 7 kg of water to 3 kg of yttrium oxide and pulverize using a bead mill to obtain an aqueous slurry containing dispersed yttrium oxide. The average primary particle size of the yttrium oxide particles in this slurry is 100 nm. Concentrate this slurry using an evaporator to obtain an aqueous slurry containing 20% ​​by mass of yttrium oxide particles.

[0326] [Manufacturing Example 9] (Particles of yttrium oxide dissolved in zirconium oxide with an average primary particle size of 40 nm)

[0327] Prepare 1.0 L of a mixed aqueous solution containing 0.62 mol / L zirconium oxychloride and 0.052 mol / L yttrium chloride, and 0.5 L of an aqueous solution containing 1.9 mol / L sodium hydroxide.

[0328] 1.0L of pure water is injected into the sedimentation tank, followed by the injection of the above-mentioned mixed aqueous solution and sodium hydroxide aqueous solution, so that zirconium oxychloride and yttrium chloride are co-precipitated to obtain a slurry.

[0329] After filtration and washing, 22.2 g of acetic acid was added to the slurry, and the mixture was subjected to hydrothermal treatment at 220°C for 3 hours. The resulting slurry was then centrifuged and filtered using a membrane filter with a pore size of 100 nm to obtain a zirconia slurry with coarse particles removed. The average primary particle size of the zirconia particles containing dissolved yttrium oxide in this slurry was 40 nm. The slurry was then concentrated using an evaporator to obtain an aqueous slurry containing 20% ​​by mass of zirconia particles dissolved in yttrium oxide.

[0330] [Manufacturing Example 10] (Particles of yttrium oxide dissolved in zirconium oxide with an average primary particle size of 15 nm)

[0331] Prepare 1.0 L of a mixed aqueous solution containing 0.62 mol / L zirconium oxychloride and 0.065 mol / L yttrium chloride, and 0.5 L of an aqueous solution containing 1.9 mol / L sodium hydroxide.

[0332] 1.0L of pure water is injected into the sedimentation tank, followed by the injection of the above-mentioned mixed aqueous solution and sodium hydroxide aqueous solution, so that zirconium oxychloride and yttrium chloride are co-precipitated to obtain a slurry.

[0333] After filtration and washing, 22.2 g of acetic acid was added to the slurry, and hydrothermal treatment was performed at 190°C for 2 hours. The resulting slurry was then centrifuged using a membrane filter with a pore size of 100 nm. Pure water was added to achieve a solids concentration (zirconia and yttrium oxide concentration) of 5.0% by mass, resulting in a zirconia slurry with coarse particles removed. The average primary particle size of the zirconia particles in this zirconia slurry was 15 nm.

[0334] [Example 1]

[0335] Using 94.6% by mass and 5.4% by mass of the slurries obtained in Manufacturing Examples 3 and 5, respectively, nine times the volume of isopropanol was added, and the mixture was placed in centrifuge tubes and thoroughly mixed, then centrifuged at 4000 rpm for 10 minutes. After confirming the precipitation of a white substance, the supernatant was removed, and isopropanol was added again and thoroughly mixed, then centrifuged at 4000 rpm for 10 minutes. After confirming the precipitation of a white substance, the supernatant was removed, and methanol was added to make it the same volume as the slurry used, and the mixture was further thoroughly mixed to obtain a methanol-displaced slurry. The residual moisture content of this methanol-displaced slurry was determined using a Karl Fischer moisture analyzer, and the result was 0.08% by mass.

[0336] In the obtained slurry, 1% by mass of glycerol (100% by mass of solid components (zirconia and yttrium oxide) and 2% by mass of acrylic binder "KFE-124" (manufactured by Muyo Chemical Industry Co., Ltd.) (100% by mass of solid components) were added, and the mixture was ultrasonically dispersed at 40 kHz for 1 hour to obtain a slurry containing additives.

[0337] The resulting slurry containing additives was supercritically dried using a supercritical drying apparatus through the following steps. Specifically, the slurry containing additives was first placed in a pressure vessel, which was then connected to a supercritical carbon dioxide extraction apparatus, ensuring there were no pressure leaks. Next, the pressure vessel and preheating tubes were immersed in a water bath heated to 60°C, then the temperature was raised to 80°C while the pressure was increased to 25 MPa, and allowed to stand for 10 minutes for stabilization. Then, under specified conditions (temperature: 80°C, pressure: 25 MPa, carbon dioxide flow rate: 10 mL / min, azeotropic agent (methanol) flow rate: 1.5 mL / min), carbon dioxide and methanol as an azeotropic agent were introduced. After 2 hours, the introduction of methanol was stopped, and only carbon dioxide was introduced. After 2 hours of carbon dioxide-only introduction, the liquid delivery of carbon dioxide was stopped, and while maintaining the temperature at 80°C, the pressure was gradually reduced from 25 MPa to atmospheric pressure over approximately 20 minutes. The pressure vessel was removed from the water bath and cooled to room temperature. The treated sample was then opened and recovered, yielding a zirconia composition containing zirconia particles and yttrium oxide particles. The yttrium oxide content in the zirconia composition was determined using a fluorescence X-ray diffraction (XRF) apparatus, and the result was 3 mol%. The particle size distribution in relation to the particle size of the obtained zirconia composition is shown below. Figure 1 Additionally, the XRD pattern of yttrium oxide in the obtained zirconium oxide composition is shown in... Figure 2 .

[0338] The obtained powder was formed into discs of a specified size using a uniaxial press, and then subjected to cold isostatic pressing (CIP) (pressure 200 MPa) to increase the density, resulting in zirconia molded bodies. Considering the shrinkage caused by sintering and the reduction in thickness caused by grinding, the size of the zirconia molded bodies was set to a diameter of 20 mm, in a manner that allows them to be processed into the size of sintered zirconia bodies described in the evaluation of the aforementioned properties. For thickness, multiple zirconia molded bodies with different sizes were manufactured.

[0339] The zirconia shaped body was pre-fired at 500°C for 2 hours under normal pressure to obtain a zirconia pre-fired body. Figure 3 A figure showing the compositional distribution (SEM-EDX) of the crystalline structure of the obtained zirconia pre-burnt body is presented.

[0340] The zirconia pre-sintered body was sintered at 1300℃ for 2 hours under normal pressure to obtain the zirconia sintered body.

[0341] [Example 2]

[0342] Except for using slurries obtained in Manufacturing Examples 2 and 6 at 94.6% and 5.4% by mass, respectively, the zirconia composition, pre-fired body, and sintered body were obtained in the same manner as in Example 1. The yttrium oxide content in the composition was determined using an XRF apparatus and found to be 3 mol%.

[0343] [Example 3]

[0344] Except for using slurries obtained in Manufacturing Examples 1 and 4 at 92.1% and 7.9% by mass, respectively, the zirconia composition, pre-fired body, and sintered body were obtained in the same manner as in Example 1. The yttrium oxide content in the composition was determined using an XRF apparatus and found to be 4.5 mol%.

[0345] [Example 4]

[0346] Except for using 86.3% by mass and 13.7% by mass of the slurries obtained in Manufacturing Examples 3 and 5, respectively, the zirconia composition, pre-fired body, and sintered body were obtained in the same manner as in Example 1. The yttrium oxide content in the composition was determined using an XRF apparatus, and the result was 8 mol%.

[0347] [Example 5]

[0348] Except for using 86.3% by mass and 13.7% by mass of the slurries obtained in Manufacturing Examples 2 and 6, respectively, the zirconia composition, pre-fired body, and sintered body were obtained in the same manner as in Example 1. The yttrium oxide content in the composition was determined using an XRF apparatus, and the result was 8 mol%.

[0349] [Comparative Example 1]

[0350] Using the slurry obtained in Manufacturing Example 9, zirconia molded bodies and pre-fired bodies were obtained in the same manner as in Example 1. The yttrium oxide content in the slurry was determined using an XRF apparatus, and the result was 4 mol%.

[0351] The pre-burnt body was placed in a Sialon container and subjected to HIP treatment in argon at a temperature of 1100°C and a pressure of 150 MPa. After cooling to room temperature, the treated material was heat-treated in air at atmospheric pressure and a temperature of 1000°C to obtain a zirconia sintered body.

[0352] [Comparative Example 2]

[0353] Using the slurry obtained in Manufacturing Example 10, zirconia molded bodies and pre-fired bodies were obtained in the same manner as in Example 1. Figure 4 A compositional distribution (SEM-EDX) diagram representing the crystalline structure of the resulting zirconia pre-sintered body is shown. The yttrium oxide content in the slurry was determined using XRF and found to be 5 mol%.

[0354] The zirconia pre-sintered body was sintered at 1100℃ for 2 hours under normal pressure to obtain the zirconia sintered body.

[0355] [Comparative Example 3]

[0356] Except for using slurries obtained in Manufacturing Examples 7 and 6 at 91.2% and 8.8% by mass, respectively, the zirconia composition, pre-fired body, and sintered body were obtained in the same manner as in Example 1. The yttrium oxide content in the composition was determined using an XRF apparatus and found to be 5 mol%.

[0357] [Comparative Example 4]

[0358] Except for using slurries obtained in Manufacturing Examples 3 and 8 at 91.2% and 8.8% by mass, respectively, the zirconia composition, pre-fired body, and sintered body were obtained in the same manner as in Example 1. The yttrium oxide content in the composition was determined using an XRF apparatus and found to be 5 mol%.

[0359] [Comparative Example 5]

[0360] As an example of Embodiment 1, which is equivalent to Patent Document 3 (International Publication No. 2020 / 179877), Comparative Example 5 is compared using the following method.

[0361] Prepare 1.0 L of 0.62 mol / L zirconium oxychloride aqueous solution, 1.0 L of 0.038 mol / L yttrium chloride aqueous solution, and 0.5 L × 2 of 1.9 mol / L sodium hydroxide aqueous solution.

[0362] Prepare two sedimentation tanks and inject 1.0L of pure water into each tank. Then, simultaneously inject zirconium oxychloride aqueous solution and sodium hydroxide aqueous solution into one sedimentation tank, and simultaneously inject yttrium chloride aqueous solution and sodium hydroxide aqueous solution into the other sedimentation tank, so that zirconium oxychloride and yttrium chloride precipitate respectively, to obtain a slurry.

[0363] After filtration and washing, 22.2 g of acetic acid was added to each slurry, and the mixture was hydrothermally treated at 200°C for 3 hours. The resulting slurries were centrifuged and filtered through a membrane filter with a pore size of 100 nm. Pure water was added to bring the solids concentration (the concentrations of zirconium oxide and yttrium oxide, respectively) to 5.0% by mass, thus preparing zirconium oxide and yttrium oxide slurries with the removal of coarse particles. The average primary particle size of the zirconium oxide and yttrium oxide particles in each slurry was 15 nm, and no particles with a diameter exceeding 100 nm could be identified. At room temperature, 0.5 L of the above-mentioned yttrium oxide slurry was slowly added dropwise to 0.5 L of the above-mentioned zirconium oxide slurry at a rate of 10 mL / min to obtain 1 L of mixed slurry. The yttrium oxide content in the slurry was determined using an XRF apparatus, and the result was 3 mol%.

[0364] The mixed slurry was poured into a plaster mold as a molding slurry. After being left at room temperature for 2 weeks, it was subjected to cold isostatic pressing (CIP) (pressure 170 MPa) to increase its density, resulting in a zirconia molded body. The plaster mold was made in the shape of a disc with a diameter of 20 mm and a thickness of 2.5 mm, based on the shape of the molded body before CIP.

[0365] It should be noted that the plaster mold was made by mixing 50% by mass of water into plaster ("Norita Dental Plaster", manufactured by Kuraraya Noritake Dental Co., Ltd.). The zirconia molded body was pre-fired at 500°C for 2 hours under normal pressure to obtain a zirconia pre-fired body.

[0366] Then, the zirconia pre-sintered body was sintered at 1100°C for 10 minutes under normal pressure to obtain a zirconia sintered body containing 3 mol% yttrium oxide.

[0367] [Comparative Example 6]

[0368] As an example of Embodiment 11, which is equivalent to Patent Document 3 (International Publication No. 2020 / 179877), Comparison Example 6 is performed using the following method.

[0369] Prepare 1.0 L of a mixed aqueous solution containing 0.62 mol / L zirconium oxychloride and 0.066 mol / L yttrium chloride, and 0.5 L of an aqueous solution containing 1.9 mol / L sodium hydroxide.

[0370] 1.0 L of pure water was injected into a sedimentation tank, followed by the simultaneous injection of the aforementioned mixed aqueous solution and sodium hydroxide aqueous solution, causing zirconium oxychloride and yttrium chloride to co-precipitate, resulting in a slurry. After filtration and washing, 22.2 g of acetic acid was added to the slurry, and hydrothermal treatment was performed at 200 °C for 1 hour. The resulting slurry was centrifuged and filtered using a membrane filter with a pore size of 100 nm. Pure water was added to bring the solids concentration (zirconia and yttrium oxide concentrations) to 5.0% by mass, producing a zirconium oxide slurry with coarse particles removed. This zirconium oxide slurry contained 0.28% by mass of zirconium oxide particles with a diameter exceeding 100 nm. The yttrium oxide content in the slurry was determined using an XRF apparatus, and the result was 5 mol%.

[0371] In addition to using the zirconia slurry obtained above as the molding slurry, zirconia molded bodies, zirconia pre-fired bodies and zirconia sintered bodies containing 5 mol% yttrium oxide were obtained in the same manner as in Comparative Example 5.

[0372] For each embodiment and comparative example, the measurement results obtained by the above method are shown in Tables 1 and 2.

[0373]

[0374]

[0375] As shown in Table 2, in Examples 1-5, it was confirmed that the generation of structural color could be suppressed, opalescence could be reduced, and light transmittance was excellent even for short-time sintering. In Examples 1-5, since at least a portion of yttrium oxide is not dissolved in zirconium oxide, the compositional distribution of the crystalline structure of the zirconium oxide pre-sintered body has a specified local content (amount) of yttrium element, therefore... Figure 3 As shown in Example 1, the crystal structure is locally irregular. After sintering, the sintered body contains a specified amount of particles larger than 100 nm, which is considered to reduce opalescence.

[0376] On the other hand, in Comparative Examples 1-3 and 5-6, the opalescence could not be reduced.

[0377] In Comparative Examples 1 and 2, zirconium and yttrium were in solid solution, and the amount of yttrium in the composition distribution was low. Therefore, as... Figure 4 As shown in Comparative Example 2, it is believed that after sintering, the sintered body forms a regular crystalline structure, and there are almost no particles larger than 100 nm in the sintered body, so the opalescence cannot be reduced.

[0378] In Comparative Example 3, due to the monoclinic crystal ratio f m The opalescence is low, therefore it is believed that it cannot reduce opalescence.

[0379] In Comparative Example 4, the average particle size of the yttrium oxide particles in the zirconium oxide composition was too large, and even with normal sintering, the light transmittance was not excellent.

[0380] Furthermore, as shown in Comparative Example 5, when yttrium oxide was produced in the liquid phase, unlike in the examples, the zirconia composition exhibited low crystallinity, preventing the peak half-width (FWHM) of the XRD pattern originating from the aforementioned stabilizer from falling within the range desired by the present invention, and also preventing the monoclinic crystallinity f in the zirconia pre-calcined body from reaching the desired range. m Within the scope desired by this invention.

[0381] Furthermore, as shown in Comparative Example 6, even when the average particle size (r1) of the zirconia particles used in the zirconia composition and the average particle size (r2) of the stabilizer particles are set to the desired ranges, the crystallinity in the zirconia composition is low, and the full width at half maximum (FWHM) of the peaks originating from the aforementioned stabilizer in the XRD pattern is not within the range desired by the present invention. Therefore, even if the monoclinic crystallinity f in the zirconia pre-sintered body can be achieved... m Within the scope desired by this invention, the local amount of stabilizer should not be within the scope desired by this invention.

[0382] Furthermore, for the zirconia sintered bodies involved in Comparative Example 2 and Example 1, a crystallography (area distribution based on the number of crystals) is shown, graphically representing the relationship between the size (area) of the crystals obtained from each grain and the number of crystals. Figure 5 .

[0383] from Figure 5 A comparison of Comparative Example 2 (left) and Example 1 (right) shows that in Example 1, there are more particles with larger particle sizes.

[0384] In Example 1, in the particle size distribution based on the number of particles, the proportion of particles with a diameter greater than 100 nm (equivalent to...) Figure 5 The "next level" portion is within the range of 3% to 15%.

Claims

1. A zirconium oxide composition comprising zirconium oxide particles and stabilizer particles capable of inhibiting the phase transformation of zirconium oxide. The average particle size r1 of the zirconium oxide particles is 1–60 nm, and the average particle size r2 of the stabilizer particles is 1–60 nm. The peak width at half maximum (FWHM) of the stabilizer-derived peaks in the powder X-ray diffraction pattern based on CuKα rays is 0.05° to 1.0°.

2. The zirconium oxide composition according to claim 1, wherein, The content of the stabilizer is 2 to 9 moles relative to the total molar number of zirconium oxide and the stabilizer.

3. The zirconium oxide composition according to claim 1 or 2, wherein, The stabilizer is yttrium oxide.

4. The zirconium oxide composition according to claim 1 or 2, wherein, The zirconium oxide particles contain a monoclinic crystal system.

5. A zirconia pre-sintered body comprising zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia, said stabilizer being yttrium oxide. At least a portion of the stabilizer is not dissolved in zirconium oxide, and the monoclinic crystal ratio f shown in the following mathematical formula (1) is... m The local presence of stabilizer in particles derived from stabilizers is 10-90 mol%, ranging from 50% to 98%. f m =I 28 / (I 28 +I 30 )*100 (1) In the formula, f m The percentage (%) of monoclinic crystals is represented by I in XRD measurements. 28 I represents the area intensity of the peak near 2θ = 28° where the main peak appears in the monoclinic crystal system. 30 This represents the area intensity of the peak near 2θ = 30° where the main peak appears in the tetragonal or cubic crystal system. The local presence of the stabilizer refers to the local presence of elements other than oxygen atoms in the oxide of the stabilizer that constitutes the particles derived from the stabilizer. It was measured using a Hitachi HIGHTEC FE-SEM Regulus 8220 field emission scanning electron microscope and an Oxford Instruments Aztec Energy X-Max 50 energy dispersive X-ray analyzer under the following conditions: zirconium oxide at 2.042 keV and yttrium at 1.923 keV. The average value of yttrium in 10 stabilizer-derived particles was calculated, in mol%. Magnification ratio: 20,000 times Analysis Mode: Point Analysis Accelerating voltage: 5kV Working distance: 15mm±1mm X-ray extraction angle: 30 degrees Dead time: 7% Measurement time: 100 seconds.

6. The zirconia pre-fired body according to claim 5, wherein, The content of the stabilizer is 2 to 9 moles relative to the total molar number of zirconium oxide and the stabilizer.

7. The zirconia pre-fired body according to claim 5 or 6, wherein, In a sintered body with a thickness of 1.2 mm after sintering at 900–1400℃ for 120 minutes, the OP value calculated using the following mathematical formula (2) is less than 15. In the formula, a ＊ 透射 and b ＊ 透射 L*a*b* represents the color coordinates of the color system in transmitted light, where a ＊ 反射 and b ＊ 反射 The L*a*b* coordinates represent the color coordinates of the color system in the reflected light.

8. The zirconia pre-fired body according to claim 5 or 6, wherein, In the sintered body after sintering at 900–1400℃ for 120 minutes, the particle size distribution based on the number of particles has at least one peak in the range of particle size above 70 nm and below 100 nm, and contains 3–15% of particles with a particle size greater than 100 nm.

9. The zirconia pre-sintered body according to claim 5 or 6, wherein the ΔL*(WB) of the sintered body with a thickness of 1.2 mm after sintering at 900–1400 °C for 120 minutes is 5 or more. The ΔL*(WB) of the zirconia sintered body was determined as follows: The ΔL*(WB) of the zirconia sintered body was determined using a CM-3610A spectrophotometer manufactured by KONICA MINOLTA JAPAN Co., Ltd. ΔL*(WB) represents the difference in lightness against a white background and against a black background. The L* value is the L* value of chromaticity 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 Part 4, Section 1 of JIS K 5600-4-1:1999, and the black background refers to the black portion of the aforementioned opacity test paper.

10. The zirconia pre-fired body according to claim 5 or 6, wherein, The first translucency ΔL1*(WB) of the first sintered body prepared by sintering at 1300℃ for 120 minutes and the second translucency ΔL2*(WB) of the second sintered body prepared by sintering at 1300℃ for 10 minutes satisfy the following mathematical expression (3). The ΔL*(WB) of zirconia sintered bodies was determined as follows: A CM-3610A spectrophotometer manufactured by KONICA MINOLTA JAPAN Co., Ltd. was used to measure the ΔL*(WB) of the zirconia sintered bodies. ΔL*(WB) represents the difference in lightness against a white background and against a black background. The L* value is the L* value of chromaticity 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 Part 4, Section 1 of JIS K 5600-4-1:1999, and the black background refers to the black portion of the aforementioned opacity test paper. ΔL2*(WB) / ΔL1*(WB)≥0.85 (3).

11. A method for manufacturing a zirconia pre-fired body, wherein the zirconia composition according to any one of claims 1 to 4 is used.

12. A zirconia sintered body comprising zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia. The stabilizer content is 2 to 9 mol% relative to the total molar number of zirconium oxide and stabilizer. The ΔL*(WB) in the sintered body with a thickness of 1.2 mm is 5 or more, and the OP value calculated using the following mathematical formula (2) is less than 15. The particle size distribution, based on the number of particles, has at least one peak in the range of 70 nm to 100 nm, and contains 3–15% particles with a diameter greater than 100 nm. In the formula, a ＊ 透射 and b ＊ 透射 L*a*b* represents the color coordinates of the color system in transmitted light, where a ＊ 反射 and b ＊ 反射 L*a*b* represents the color coordinates of the color system in reflected light. The ΔL*(WB) of the zirconia sintered body was determined as follows: The ΔL*(WB) of the zirconia sintered body was determined using a CM-3610A spectrophotometer manufactured by KONICA MINOLTA JAPAN Co., Ltd. ΔL*(WB) represents the difference in lightness against a white background and against a black background. The L* value is the L* value of chromaticity 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 Part 4, Section 1 of JIS K 5600-4-1:1999, and the black background refers to the black portion of the aforementioned opacity test paper.

13. The zirconia sintered body according to claim 12, wherein, The stabilizer is yttrium oxide.

14. A method for manufacturing a zirconia sintered body, wherein the zirconia composition according to any one of claims 1 to 4 or the zirconia pre-sintered body according to any one of claims 5 to 10 is used.

15. The method for manufacturing a zirconia sintered body according to claim 14, comprising a sintering step at 900–1400°C.

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