Zirconia composition and method for producing same

Abstract

The present invention provides: a zirconia composition, a zirconia sintered body of which has excellent mechanical strength, and which is capable of controlling opalescence to an appropriate range; and a method for producing the same. The present invention relates to a zirconia composition comprising zirconia particles having a zirconia concentration of 80 mass% or more, and small particles having a stabilizer concentration of 10-50 mass%. The small particles have a primary particle diameter that is smaller than the average primary particle diameter of the zirconia particles.

Description

Zirconia composition and method for producing the same

[0001] The present invention relates to a zirconia composition and a method for producing the same. More specifically, the present invention relates to a zirconia composition that provides a zirconia sintered body having excellent mechanical strength and that can control opalescence within an appropriate range, and a method for producing the same.

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

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

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

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

[0006] International Publication No. 2022 / 138881

[0007] However, in the case of a zirconia sintered body obtained using the zirconia calcined body according to Patent Document 1, when the crystalline structure is simply kept small, a so-called structural color is generated (hereinafter, this characteristic will be referred to as "opalescence"), which appears to be colored by selectively reflecting or transmitting a specific wavelength due to the uniform structure, and this has room for improvement in terms of having an appearance closer to the color tone of natural teeth.

[0008] An object of the present invention is to provide a zirconia composition in which the resulting zirconia sintered body has excellent mechanical strength and the opalescence can be controlled within an appropriate range, and a method for producing the same.

[0009] As a result of intensive research to solve the above problems, the present inventors have found that by using a zirconia composition comprising zirconia particles having a zirconia concentration of 80 mass % or more and small particles having a stabilizer capable of suppressing the phase transition of zirconia at a concentration of 10 to 50 mass %, wherein the small particles have a primary particle size smaller than the average primary particle size of the zirconia particles, the resulting zirconia sintered body has excellent mechanical strength and the opalescence can be controlled within an appropriate range. Based on this finding, the present inventors have conducted further research and have completed the present invention.

[0010] The present invention encompasses the following: [1] A zirconia composition comprising zirconia particles having a zirconia concentration of 80% by mass or more and small particles having a stabilizer capable of suppressing the phase transition of zirconia at a concentration of 10 to 50% by mass, the small particles having a primary particle size smaller than the average primary particle size of the zirconia particles. [2] The zirconia composition according to [1], wherein, under TEM observation, 10 small particles are randomly selected, and at least 6 of the 10 small particles have a stabilizer concentration of 10 to 50% by mass. [3] The zirconia composition according to [1] or [2], wherein the average primary particle size of the zirconia particles is 0.06 to 0.17 μm. [4] The zirconia composition according to any of [1] to [3], wherein the average primary particle size of the small particles is less than 0.06 μm. [5] The zirconia composition according to any one of [1] to [4], wherein the stabilizer capable of suppressing the phase transition of zirconia is yttria. [6] The zirconia composition according to any one of [1] to [5], wherein the area ratio of the zirconia particles to the small particles is 55 / 45 to 99 / 1 under TEM observation. [7] A method for producing a zirconia composition according to any one of [1] to [6], comprising: a step of producing a raw material composition containing zirconia particles and particles of a stabilizer capable of suppressing the phase transition of zirconia; and a grinding step of grinding the zirconia composition, wherein the grinding step uses grinding media with a diameter of less than 1 mm. [8] The method for producing a zirconia composition according to [7], wherein the treatment time in the grinding step is 20 minutes to 2 hours. [9] The method for producing a zirconia composition according to [7] or [8], wherein the zirconia particles have an average primary particle size of 0.06 to 0.17 μm.

[10] The method for producing a zirconia composition according to any one of [7] to [9], wherein the small particles have an average primary particle size of less than 0.06 μm.

[11] The method for producing a zirconia composition according to any one of [7] to

[10] , wherein the stabilizer capable of suppressing the phase transition of zirconia is yttria.

[12] The method for producing a zirconia composition according to any one of [7] to

[11] , further comprising a step of producing a slurry containing the raw material composition, and spray-drying the slurry to granulate.

[0011] According to the present invention, it is possible to provide a zirconia composition and a method for producing the same, which produce a zirconia sintered body having excellent mechanical strength and capable of controlling opalescence within an appropriate range. Furthermore, by using the zirconia calcined body of the present invention, it is possible to obtain a zirconia sintered body having excellent mechanical strength and translucency at a maximum sintering temperature lower than conventional temperatures (for example, 1,450°C or lower). Furthermore, by using the zirconia calcined body of the present invention, it is possible to provide a zirconia sintered body having excellent mechanical strength and translucency without using a HIP apparatus.

[0012] [Zirconia Composition] The zirconia composition of the present invention comprises zirconia particles having a zirconia concentration of 80 mass % or more and small particles (hereinafter also simply referred to as "small particles") having a stabilizer capable of suppressing the phase transition of zirconia at a concentration of 10 to 50 mass %, wherein the small particles have a primary particle diameter smaller than the average primary particle diameter of the zirconia particles.

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

[0014] The reason why the concentration of a stabilizer capable of suppressing the phase transition of zirconia in the small particles contained together with the zirconia particles in the zirconia composition of the present invention is 10 to 50 mass % enables the resulting zirconia sintered body to have excellent mechanical strength and control of opalescence within an appropriate range is unclear, but is presumed to be as follows: By including small particles containing a stabilizer capable of suppressing the phase transition of zirconia in the zirconia composition at a concentration of 10 to 50 mass % together with the zirconia particles, it is possible to improve the uneven distribution of the stabilizer in the zirconia composition, which was not possible with conventional undissolved zirconia (zirconia in which the stabilizer is not dissolved). As a result, the resulting sintered body has a sintered structure with a relatively uniform crystal grain size and composition, which is thought to result in a sintered body with excellent mechanical strength and opalescence controlled within an appropriate range.

[0015] [Method for Producing Zirconia Composition] The zirconia composition of the present invention can be produced by subjecting a raw material zirconia composition (hereinafter also referred to as the "raw material composition" or the "zirconia composition before pulverization treatment") containing zirconia particles and particles of a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as the "stabilizer") to a pulverization treatment under predetermined conditions, in which excess energy is applied compared to that in conventional techniques.

[0016] Examples of stabilizers capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizers") include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (YO), cerium oxide (CeO), scandium oxide (ScO), niobium oxide (NbO), lanthanum oxide (LaO), erbium oxide (ErO), praseodymium oxide (PrO, PrO) and the like. 11Examples of suitable stabilizers include yttria (Y2O3), samarium oxide (Sm2O3), europium oxide (Eu2O3), thulium oxide (Tm2O3), gallium oxide (Ga2O3), indium oxide (In2O3), and ytterbium oxide (Yb2O3), with yttria (Y2O3) being preferred. The stabilizers may be used alone or in combination of two or more. The zirconia composition of the present invention may contain only yttria (Y2O3), or may further contain yttria and a stabilizer other than yttria that can suppress the phase transition of zirconia.

[0017] The content of the stabilizer in the zirconia composition is preferably 2.5 mol% or more, more preferably 3.0 mol% or more, even more preferably 3.5 mol% or more, and particularly preferably 4.0 mol% or more, based on the total moles of zirconia and stabilizer. A content of 2.5 mol% or more is preferable in that the crystal system contained in the sintered body contains more cubic crystals, improving translucency. Furthermore, the content of the stabilizer is preferably 10 mol% or less, more preferably 9.0 mol% or less, even more preferably 8.5 mol% or less, and particularly preferably 8 mol% or less. A content of 10 mol% or less is preferable in that it prevents a decrease in strength.

[0018] The method for producing a zirconia composition will be described below by taking as an example a case where the stabilizer is yttria.

[0019] The zirconia composition (raw material composition) before pulverization can be produced by mixing raw material powders, zirconia powder and yttria powder. The mixing method is not particularly limited, and known methods and devices can be used.

[0020] As a method for preparing the zirconia particles constituting the zirconia powder and the yttria particles constituting the yttria powder, for example, a breakdown process in which coarse particles are pulverized or crushed to form fine particles, or a building-up process in which atoms or ions are synthesized through a nucleation and growth process, can be employed. However, considering that even when produced by the building-up process, a predetermined pulverization process is required to adjust the concentration of the stabilizer in the small particles to a desired range, the breakdown process is preferred from the viewpoint of ease of production.

[0021] The method for producing a zirconia composition will be described below using a breakdown process as an example.

[0022] The zirconia constituting the zirconia powder preferably contains monoclinic zirconia. In one embodiment, the zirconia constituting the zirconia powder contains monoclinic zirconia and may further contain tetragonal zirconia and / or cubic zirconia. In another embodiment, the zirconia constituting the zirconia powder may contain tetragonal zirconia and / or cubic zirconia, but may not contain monoclinic zirconia. In the zirconia powder, one of these crystal systems may be used alone, or two or more may be used in combination.

[0023] As the zirconia powder raw material powder, commercially available zirconia particles may be used, or the commercially available powder may be used after being pulverized in a known pulverizing / mixing device (such as a ball mill).As the yttria powder raw material powder, commercially available yttria particles may be used, or the commercially available powder may be used after being pulverized in a known pulverizing / mixing device (such as a ball mill).

[0024] Commercially available zirconia powders include, for example, zirconia powders (trade names "Zpex (registered trademark)" (Y2O3 content: 3 mol%), "Zpex (registered trademark) 4" (Y2O3 content: 4 mol%), and "Zpex (registered trademark) Smile (registered trademark)" (YO content: 5.5 mol%), "TZ-3Y" (YO content: 3 mol%), "TZ-3YS" (YO content: 3 mol%), "TZ-4YS" (YO content: 4 mol%), "TZ-6Y" (YO content: 6 mol%), "TZ-6YS" (YO content: 6 mol%), "TZ-8YS" (YO content: 8 mol%), "TZ-10YS" (YO content: 10 mol%), "TZ-3Y-E" (YO content: 3 mol%), "TZ- Examples of such zirconia include "TZ-3YS-E" (YO content: 3 mol%), "TZ-3YB-E" (YO content: 3 mol%), "TZ-3YSB-E" (YO content: 3 mol%), "TZ-3YB" (YO content: 3 mol%), "TZ-3YSB" (YO content: 3 mol%), "TZ-3Y20AB" (YO content: 3 mol%), "TZ-8YSB" (YO content: 8 mol%), and "TZ-0" (YO content: 0 mol%; monoclinic zirconia); all manufactured by Tosoh Corporation.

[0025] Next, the zirconia composition containing zirconia particles and stabilizer particles is subjected to a pulverization process. By applying an excess amount of energy compared to conventional techniques during the pulverization process under specified conditions, a zirconia composition containing zirconia particles and small particles with a stabilizer concentration adjusted to a desired range is obtained. Conventionally, zirconia particles are a substance with extremely high hardness, so even if the amount of energy used in the pulverization process is increased, it is difficult to reduce the size of the zirconia particles to excessively small sizes. Therefore, there has been no technical significance in excessively pulverizing the zirconia particles. However, in the present invention, when a zirconia composition containing zirconia and yttria is subjected to a specified pulverization process, the stabilizer concentration in the small particles can be adjusted to a desired range. Therefore, it is presumed that, when a sintered body is produced, not only will the opalescence be excellent, but the opalescence can be controlled within an appropriate range, resulting in excellent aesthetics.

[0026] By adjusting the stabilizer concentration in the small particles to a desired range, the final sintered body not only has excellent mechanical strength, but also allows the opalescence to be controlled within an appropriate range, resulting in excellent aesthetics. To achieve this, excessive energy is applied to the zirconia composition. As a result of the progress of disintegration and grinding in this grinding process, the zirconia and yttria particles are finely divided and their mixing is promoted, allowing the stabilizer concentration in the small particles in the resulting zirconia composition to be adjusted to a desired range. Furthermore, during this grinding process, the dissolution and amorphization of yttria progress, allowing the proportion of undissolved yttria to be adjusted to the desired range as calculated by Equation (1-1). As long as the zirconia composition contains small particles with a stabilizer concentration adjusted to a desired range and zirconia particles, the final sintered body has excellent mechanical strength and the opalescence can be controlled within an appropriate range. Therefore, the proportion of undissolved yttria is not particularly limited. The proportion of undissolved yttria can be controlled by adjusting the grinding time.

[0027] When using grinding media with a diameter of less than 1 mm, the grinding media diameter (diameter) is preferably 0.1 to 0.5 mm, since using grinding media with a fine diameter makes it easier to increase the amount of energy used in the grinding process and makes it easier to adjust the concentration of the stabilizer in the small particles to a desired range. Commercially available grinding media with a diameter of less than 1 mm may be used. Examples of grinding devices that use grinding media with a diameter of less than 1 mm include bead mills.

[0028] When grinding media with a diameter of less than 1 mm are used, the grinding time is not particularly limited as long as a zirconia composition containing zirconia particles having a zirconia concentration of 80% by mass or more and small particles having a stabilizer concentration of 10 to 50% by mass is obtained. However, in order to easily adjust the stabilizer concentration in the small particles to the desired range, the grinding time is preferably 10 minutes or more, more preferably 15 minutes or more, even more preferably 20 minutes or more, and particularly preferably 30 minutes or more. In addition, in order to easily adjust the stabilizer concentration in the small particles to the desired range, the grinding time is preferably 20 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and particularly preferably 2 hours or less. Note that when a grinding device that grinds while circulating a slurry (e.g., a circulating bead mill) is used as the grinding device, the grinding time refers to the residence time of the slurry in the vessel (grinding chamber).

[0029] In the present invention, by supplying to the zirconia composition increased milling treatment energy adjusted by the combination of the milling time and the milling media diameter, it is possible to obtain a zirconia composition containing small particles having a stabilizer concentration adjusted to a desired range and zirconia particles.

[0030] By producing a zirconia calcined body using a zirconia composition containing zirconia particles and small particles in which the concentration of the stabilizer has been adjusted to a desired range, and then producing a zirconia sintered body, it is presumed that the resulting sintered body will not only have excellent mechanical strength, but will also be able to control the opalescence within an appropriate range and exhibit excellent aesthetic properties.

[0031] The concentration of the stabilizer in the small particles contained in the zirconia composition after the milling treatment is preferably 10% by mass or more, more preferably 10.5% by mass or more, even more preferably 11% by mass or more, and particularly preferably 11.5% by mass or more, because this provides excellent mechanical strength and makes it easier to control the opalescence within an appropriate range. Furthermore, the concentration of the stabilizer in the small particles is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less, because this provides excellent mechanical strength and makes it easier to control the opalescence within an appropriate range.

[0032] The zirconia composition after the grinding treatment can also form a small particle group containing a plurality of small particles in which the concentration of the stabilizer is adjusted to a desired range, as long as the effect of controlling the opalescence within an appropriate range is achieved.

[0033] The concentration of the stabilizer in the small particle group is preferably 10 to 50% by mass, since this provides excellent mechanical strength and makes it easier to control the opalescence within an appropriate range. The concentration of the stabilizer in the small particle group is preferably the same as the concentration of the stabilizer in the small particles contained in the zirconia composition. Furthermore, the concentration of zirconia in the small particle group is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, and particularly preferably 65% ​​by mass or more, from the viewpoint of providing excellent mechanical strength in combination with the concentration of the stabilizer in the small particles and making it easier to control the opalescence within an appropriate range. Furthermore, the concentration of zirconia in the small particle group is preferably 90% by mass or less, more preferably 89.5% by mass or less, even more preferably 89% by mass or less, and particularly preferably 88.5% by mass or less, from the viewpoint of providing excellent mechanical strength in combination with the concentration of the stabilizer in the small particles and making it easier to control the opalescence within an appropriate range.

[0034] The zirconia composition after the milling treatment has excellent mechanical strength and can easily control the opalescence within an appropriate range. Therefore, under observation with a transmission electron microscope (TEM), ten small particles are arbitrarily selected from one field of view at a magnification of 200,000 times, and six or more of the ten small particles have a stabilizer concentration of 10 to 50 mass%. Of the ten small particles, seven or more small particles having a stabilizer concentration of 10 to 50 mass% are more preferably selected, eight or more are even more preferably selected, nine or more are particularly preferably selected, and ten are most preferably selected. If ten small particles cannot be obtained from one field of view, the number of fields of view may be increased to select a total of ten small particles. Similarly, in this specification, when selecting a specific number of small particles (e.g., 10) from one field of view, if the desired number of particles cannot be confirmed in one field of view, the number of fields of view may be increased to two or more, and the desired total number (e.g., 10) may be selected. For example, when selecting 100 particles, 10 particles may be arbitrarily selected from 4 visual fields, and this may be repeated until the target number of 100 particles is reached. Furthermore, when 10 small particles are arbitrarily selected under TEM observation and observed in 10 visual fields, the zirconia composition preferably contains the above number of small particles in 6 or more visual fields, more preferably contains the above number of small particles in 8 or more visual fields, still more preferably contains the above number of small particles in 9 or more visual fields, and particularly preferably contains the above number of small particles in all 10 visual fields. In a preferred embodiment, a zirconia composition is preferred in which, out of 100 particles (for example, any 10 particles × 10 fields of view in one field of view at a magnification of 200,000), 60 or more are small particles having a stabilizer concentration of 10 to 50 mass %, more preferably 70 or more, even more preferably 80 or more, particularly preferably 90 or more, and most preferably 100. In the present invention, the number of objects to be observed under TEM may be 200 or more, or 500 or more, as needed.

[0035] The zirconia composition after the pulverization treatment has excellent mechanical strength and allows easy control of opalescence within an appropriate range. Therefore, under TEM observation, the area ratio (%) of the zirconia particles to the small particles, zirconia particles / small particles, is preferably 55 / 45 to 99 / 1, more preferably 65 / 35 to 98 / 2, even more preferably 70 / 30 to 97 / 3, and particularly preferably 75 / 25 to 95 / 5.

[0036] The zirconia composition before and after the pulverization treatment may be in the form of granules, a slurry, etc. When the zirconia composition is a slurry, the slurry can be produced by mixing the mixed powder obtained by the pulverization treatment with a solvent (preferably water).

[0037] The zirconia composition may also contain additives such as a binder, a dispersant, an emulsifier, an antifoaming agent, a pH adjuster, a lubricant, a translucency adjuster, etc. The additives may be used alone or in combination of two or more.

[0038] Examples of binders include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.

[0039] In order to improve translucency, the content of the binder in the zirconia composition of the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, relative to 100% by mass of zirconia.

[0040] Examples of the plasticizer include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

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

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

[0043] Examples of the antifoaming agent include alcohol, polyether, polyethylene glycol, silicone, and wax.

[0044] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide).

[0045] Examples of the lubricant include polyoxyethylene alkyl ether and wax.

[0046] Examples of the light transmittance adjusting agent include aluminum oxide (Al2O3), titanium oxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0047] The BET specific surface area of ​​the particles constituting the zirconia composition is 7.0 m when measured in accordance with JIS Z 8830:2013. 2 / g or more, and 7.5m 2 / g or more, and more preferably 8.0m 2 / g or more is more preferable. 2 / g or more, the sintered body is easily prevented from becoming cloudy when sintered. 2 / g or less, and 2 / g or less is more preferable, and 40m2 / g or less is more preferable. 2 / g or less, the BET specific surface area is less susceptible to temperature variations in the firing furnace. The BET specific surface area can be measured using a commercially available product such as a fully automatic specific surface area measuring device (trade name "Macsorb (registered trademark) HM model-1200", BET flow method (single-point method / multi-point method), manufactured by Mountec Co., Ltd.). For example, it can be measured by the BET flow method (single-point method) using the fully automatic specific surface area measuring device. Furthermore, even when the firing time for sintering is shortened, the light transmittance of the sintered body is less likely to decrease. The "BET specific surface area" referred to here is a specific surface area measured without distinguishing between primary particles and secondary particles.

[0048] The average particle size of the zirconia composition after the pulverization treatment is preferably 0.2 μm or less, since the sintered body has excellent mechanical strength and the opalescence can be controlled within an appropriate range.

[0049] The average particle size of the zirconia particles and yttria particles in the zirconia composition after the pulverization treatment can be measured by a dynamic light scattering particle size distribution measurement method. For example, using a dynamic light scattering particle size distribution measurement device (product name "SZ-100V2") manufactured by Horiba, Ltd., a slurry diluted to about 0.1 mass % with water is irradiated with ultrasonic waves for 30 minutes, and then the average particle size can be measured on a volume basis while applying ultrasonic waves.

[0050] The average primary particle size of the zirconia particles contained in the zirconia composition after the pulverization treatment is preferably 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.06 μm or more, and is preferably 0.20 μm or less, more preferably 0.19 μm or less, and even more preferably 0.17 μm or less.

[0051] The average primary particle size of the small particles contained in the zirconia composition after the pulverization treatment is preferably less than 0.06 μm, more preferably 0.05 μm or less, and even more preferably 0.04 μm or less.

[0052] Next, the pulverized zirconia composition is subjected to a molding step to produce a molded body, which is obtained by applying an external force to the zirconia composition using a known method.

[0053] The molding method is not particularly limited, and the following methods can be used, for example: (a) a step of slip-casting a slurry containing the pulverized zirconia composition; (b) a step of gel-casting a slurry containing the pulverized zirconia composition; (c) a step of press-molding the pulverized zirconia composition; (d) a step of molding a zirconia composition containing zirconia particles, small particles, and a resin; (e) a step of polymerizing a zirconia composition containing zirconia particles, small particles, and a polymerizable monomer or oligomer; and (f) a step of additive manufacturing of granules containing the zirconia particles and small particles.

[0054] (a) Slip Casting When a zirconia molded body is produced by a method including a step of slip-casting a slurry containing a zirconia composition after a pulverization treatment, the specific slip-casting method is not particularly limited. For example, a method in which the slurry is poured into a mold and then dried can be employed. The content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, because this facilitates pouring the slurry into the mold, prevents the drying process from taking a long time, and allows the mold to be used more frequently. The slurry may be poured into the mold under normal pressure, but from the viewpoint of production efficiency, it is preferable to pour the slurry into the mold under pressurized conditions.

[0055] (b) Gel Casting When a zirconia molded body is produced by a method including a step of gel-casting a slurry containing a zirconia composition after a pulverization treatment, the specific gel-casting method is not particularly limited. For example, a method can be employed in which the slurry is gelled in a mold to obtain a shaped wet body, and then this is dried. The content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, in order to prevent a long drying time and to suppress the occurrence of cracks during drying. Gelation can be carried out, for example, by adding a gelling agent or by adding a polymerizable monomer and then polymerizing it.

[0056] There is no limitation on the type of gelling agent, and for example, a water-soluble gelling agent can be used, and specifically, agarose, gelatin, etc. can be preferably used. A single gelling agent may be used alone, or two or more types may be used in combination. The amount of gelling agent used is not particularly limited as long as problems such as cracking do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less based on the mass of the slurry after the gelling agent is blended.

[0057] The type of polymerizable monomer is not particularly limited, and examples thereof include (meth)acrylate monomers such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; and (meth)acrylamide monomers such as N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N,N-bis(2-hydroxyethyl) (meth)acrylamide. One type of polymerizable monomer may be used alone, or two or more types may be used in combination. The amount of polymerizable monomer used is not particularly limited as long as problems such as cracking do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less, based on the mass of the slurry after the polymerizable monomer is blended.

[0058] When gelation is carried out by polymerization of a polymerizable monomer, the polymerization is preferably carried out using a polymerization initiator. There are no particular restrictions on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred.

[0059] Specific examples of the photopolymerization initiator include (bis)acylphosphine oxides (including salts), thioxanthones (including salts such as quaternary ammonium salts), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ether compounds, and α-aminoketone compounds. One photopolymerization initiator may be used alone, or two or more may be used in combination. Among these photopolymerization initiators, it is preferable to use at least one selected from the group consisting of (bis)acylphosphine oxides and α-diketones. This allows polymerization (gelation) to occur in both the ultraviolet (including near-ultraviolet) and visible light regions, and in particular, polymerization (gelation) can be sufficiently performed using any light source, such as a laser (e.g., Ar laser, He—Cd laser), or lighting (e.g., halogen lamp, xenon lamp, metal halide lamp, light-emitting diode (LED), mercury lamp, or fluorescent lamp.

[0060] The drying method for drying the shaped wet body is not particularly limited, and examples thereof include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. These may be used alone or in combination. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred because they can suppress the occurrence of cracks during drying.

[0061] There are no particular limitations on the type of mold used in slip casting and gel casting, and for example, porous molds made of plaster, resin, ceramics, etc., and non-porous molds made of metal, resin, etc. can be used.

[0062] (c) Press Molding In the step of press molding the zirconia composition after the pulverization treatment, the specific press molding method is not particularly limited, and can be performed using a known press molding machine. Specific examples of the press molding method include uniaxial pressing.

[0063] Alternatively, multi-stage molding may be performed. For example, after press-molding the zirconia composition, a cold isostatic pressing (CIP) treatment may be further performed.

[0064] The shape of the molded body is not particularly limited and may be a disk, a rectangular parallelepiped, or a dental product shape (e.g., a crown shape). The molded body may be, for example, a columnar zirconia molded body obtained by filling a mold with a zirconia composition (e.g., granules) and compacting it with a uniaxial press. The higher the surface pressure in the press molding, the higher the density of the molded body. On the other hand, if the density of the zirconia molded body is too high, the zirconia calcined body will become hard. Therefore, the surface pressure in the press molding when producing the zirconia molded body is preferably 30 to 200 MPa. When the surface pressure in the press is 30 MPa or more, the shape retention of the zirconia molded body is excellent, and when it is 200 MPa or less, the density of the zirconia molded body does not increase too much, making it easier to prevent hardening.

[0065] The molded body also includes a molded body densified by a high-temperature pressure treatment such as CIP (Cold Isostatic Pressing). From the same viewpoint as above, the pressure of the CIP is preferably 30 to 200 MPa.

[0066] (d) Molding of a zirconia composition containing a resin When a zirconia molded body is produced by a method including a step of molding a zirconia composition containing zirconia particles, small particles, and a resin, the specific method for molding the zirconia composition is not particularly limited, and for example, injection molding, cast molding, extrusion molding, etc. can be used. Furthermore, a method of molding the composition by fusion dynamic molding (FDM), an inkjet method, a powder / binder lamination method, or other additive manufacturing methods (3D printing, etc.) may also be used. Among these molding methods, injection molding and cast molding are preferred, and injection molding is more preferred. The type of resin is not particularly limited, and it is preferable to use the binder described above.

[0067] (e) Polymerization of a zirconia composition containing zirconia particles, small particles, and a polymerizable monomer or oligomer. Polymerization of a zirconia composition containing zirconia particles, small particles, and a polymerizable monomer or oligomer polymerizes the polymerizable monomer or oligomer in the composition, thereby hardening the composition. When producing a zirconia molded body using a method including this polymerization step, the specific method is not particularly limited. For example, a method of polymerizing a zirconia composition in a mold or a stereolithography (SLA) method using a zirconia composition can be employed. Among these, the stereolithography (SLA) method (b) is preferred. Stereolithography allows the zirconia molded body to be given a shape corresponding to the desired shape of the final zirconia sintered body during production. Therefore, stereolithography may be particularly suitable when the zirconia sintered body is used as a dental material for dental prostheses, etc. The type of polymerizable monomer is not particularly limited, and may be any of monofunctional polymerizable monomers such as monofunctional (meth)acrylates and monofunctional (meth)acrylamides, and polyfunctional polymerizable monomers such as bifunctional aromatic compounds, bifunctional aliphatic compounds, and trifunctional or higher compounds. One type of polymerizable monomer may be used alone, or two or more types may be used. Among these, it is preferable to use a polyfunctional polymerizable monomer, particularly when a stereolithography method is employed. The oligomer is not particularly limited as long as it is a compound in which two or more of the above polymerizable monomers are bonded and has polymerizability.

[0068] Examples of monofunctional (meth)acrylates include (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and sec-butyl (meth)acrylate. alkyl (meth)acrylates such as acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate; alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic group-containing (meth)acrylates such as benzyl (meth)acrylate and phenyl (meth)acrylate; and (meth)acrylates having a functional group such as 2,3-dibromopropyl (meth)acrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, and 11-(meth)acryloyloxyundecyltrimethoxysilane. Examples of monofunctional (meth)acrylamides include (meth)acrylamide, N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-di-n-propyl(meth)acrylamide, N,N-di-n-butyl(meth)acrylamide, N,N-di-n-hexyl(meth)acrylamide, N,N-di-n-octyl(meth)acrylamide, N,N-di-2-ethylhexyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and N,N-bis(2-hydroxyethyl)(meth)acrylamide.Among these monofunctional polymerizable monomers, (meth)acrylamide is preferred because of its excellent polymerizability, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.

[0069] Examples of the bifunctional aromatic compound include 2,2-bis((meth)acryloyloxyphenyl)propane, 2,2-bis[4-(2-hydroxy-3-acryloyloxy-2-hydroxypropoxy)phenyl]propane, 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (commonly known as "Bis-GMA"), 2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane, 2, Examples of (meth)acrylates include 2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, and 1,4-bis(2-(meth)acryloyloxyethyl)pyromellitate. Among these, Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article. Of the 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propanes, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average number of moles of ethoxy groups added: 2.6, commonly known as "D-2.6E") is preferred.

[0070] Examples of the bifunctional aliphatic compounds include glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of (meth)acrylates include triethylene glycol dimethacrylate (TEGDMA) and UDMA, which are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0071] Examples of tri- or higher functional compounds include (meth)acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacryloyloxy-2,2,6,6-tetra(meth)acryloyloxymethyl-4-oxaheptane. Among these, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetramethacrylate and 1,7-diacryloyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxaheptane are preferred in terms of excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0072] In any of the above methods, the polymerization of the composition is preferably carried out using a polymerization initiator, and the composition preferably further contains a polymerization initiator. There are no particular limitations on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred. Specific examples of photopolymerization initiators are the same as those described above in the explanation of gel casting.

[0073] When a zirconia molded body is produced by stereolithography using the pulverized zirconia composition, the specific method of stereolithography is not particularly limited, and any known method can be appropriately employed for stereolithography. For example, a method can be employed in which a liquid composition is photopolymerized using an optical lithography device with ultraviolet light, a laser, or the like to sequentially form layers having the desired shape, thereby obtaining the desired zirconia molded body.

[0074] To further improve the density of the cured zirconia molded body, the zirconia molded body may be subjected to a humidification treatment followed by a CIP treatment. When press molding is performed, a powder containing zirconia particles may be humidified before press molding, followed by press molding. The humidification method may be any known method, including spraying water with a spray bottle or using a hygrostat or thermo-hygrostat. The moisture content of the humidification treatment varies depending on the average particle size of the zirconia particles and the average particle size of the stabilizer particles, but is preferably greater than 2% by mass, more preferably greater than 3% by mass, even more preferably greater than 4% by mass, and particularly preferably greater than 5% by mass, relative to the mass of the powder before humidification (powder before humidification treatment) and the molded body. It is also preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 11% by mass or less. The moisture content of the powder after humidification can be calculated as a percentage by subtracting the mass of the powder before humidification and the compact from the mass of the wet powder (powder after humidification) and the compact, and dividing the result by the mass of the powder before humidification and the compact. The pressure for the CIP treatment is the same as that described above in the description of press molding.

[0075] (f) Step of additive manufacturing of granules containing zirconia particles and small particles When manufacturing granules containing zirconia particles and small particles, there are no particular limitations on the specific method. For example, a method can be used in which the granules are slurried and then dried with a spray dryer to form granules, and the resulting granules can be used for powder additive manufacturing. There are no particular limitations on the powder additive manufacturing method, but examples include the powder bed method, the SLS method (selective laser sintering method), the SLM method (selective laser melting method), the electron beam method, the arc discharge method, and the binder jet method. For methods in which it is preferable to not use organic substances during additive manufacturing, it is preferable not to use organic substances even in the granule manufacturing stage.

[0076] [Method for Producing Zirconia Calcined Body] Next, a method for producing a zirconia calcined body will be described, taking the case where the stabilizer is yttria as an example. The zirconia calcined body of the present invention can be produced by pulverizing a zirconia composition, shaping the pulverized zirconia composition into a molded body, calcining the molded body to an extent that the zirconia particles do not sinter together, and applying excess energy compared to conventional techniques to the pulverization under specified conditions.

[0077] The calcination temperature (maximum calcination temperature) in the calcination step is preferably 600°C or higher, more preferably 700°C or higher, even more preferably 800°C or higher, and particularly preferably 850°C or higher, from the viewpoint of ensuring a semi-sintered state using the specific zirconia composition described above. Furthermore, the calcination temperature is preferably 1200°C or lower, more preferably 1150°C or lower, even more preferably 1100°C or lower, and particularly preferably 1050°C or lower, from the viewpoint of ensuring workability. That is, in the method for producing a zirconia calcined body of the present invention, the temperature is preferably 600°C to 1200°C. Furthermore, by incorporating small particles having a stabilizer concentration within a predetermined range through the pulverization treatment, the desired calcined body can be obtained even at a lower temperature range than conventionally (for example, about 600 to 900°C).

[0078] The holding time (holding time) at the maximum calcination temperature is not particularly limited as long as a semi-sintered zirconia calcined body can be obtained, but it is preferable to hold the temperature at the maximum calcination temperature for 30 minutes to 6 hours. Furthermore, the heating rate to the maximum calcination temperature and the heating rate from the maximum calcination temperature are preferably 300°C / min or less. In a preferred embodiment, the heating rate to the maximum calcination temperature when calcining the zirconia molded body of the present invention is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more, and is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. A heating rate above the lower limit improves productivity. Furthermore, by keeping the temperature rise rate at or below the above upper limit, the difference in volume between the inside and outside of the zirconia molded body or the zirconia calcined body can be suppressed, and if the zirconia molded body contains an organic substance, rapid decomposition of the organic substance can be suppressed, thereby suppressing cracks and breakage.

[0079] [Zirconia Calcined Body] Next, the zirconia calcined body will be described. The zirconia calcined body is obtained by calcining the zirconia molded body obtained as described above.

[0080] The type and content of the stabilizer in the zirconia calcined body are the same as those in the zirconia composition.

[0081] Furthermore, the zirconia calcined body of the present invention is not particularly limited because the zirconia sintered body obtained by using the zirconia composition has excellent mechanical strength and can control the opalescence within an appropriate range. However, in one embodiment, the zirconia calcined body of the present invention has a monoclinic crystal fraction of zirconia within a predetermined range, and the obtained sintered body may have even better mechanical strength and translucency. Therefore, the abundance ratio f of yttria that is not dissolved in zirconia (hereinafter, also simply referred to as "undissolved yttria") calculated by the following formula (1-1) is preferably 0.05: y (%) is preferably less than 4%. y (%) = I y / (I m +I t+I c +I y )×100 (1-1) (where f y represents the abundance (%) of yttria not dissolved in zirconia, and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2°, where the peak top of the main peak of yttria not dissolved in zirconia appears. Note that, since the positions of the main peaks of the tetragonal and cubic systems are similar, the integrated intensity of each main peak is calculated by peak separation.)

[0082] Undissolved yttria abundance f y The content of undissolved yttria f (%) is more preferably less than 3.5%, even more preferably 2% or less, and particularly preferably 1% or less, in order to obtain a zirconia sintered body having excellent mechanical strength and translucency, in addition to the fact that the half-width is within a predetermined range. y The undissolved yttria content f (%) may be 0%. y (%) can be adjusted by a grinding process or the like, as described below.

[0083] Furthermore, the zirconia calcined body of the present invention is not particularly limited because the zirconia sintered body obtained by using the zirconia composition has excellent mechanical strength and can control the opalescence within an appropriate range. However, in one embodiment, the zirconia calcined body of the present invention is integrated with small particles having a stabilizer concentration adjusted to a desired range, and the obtained sintered body may have even better mechanical strength and translucency. Therefore, the monoclinic fraction f calculated by the formula (1-2) is preferably 0.01. m (%) is preferably less than 55%. m (%) = I m / (I m +I t +I c +I y )×100 (1-2) (where f m represents the monoclinic crystal ratio (%), and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2° where the peak top of the main peak of undissolved yttria appears. Note that, since the positions of the main peaks of the tetragonal and cubic crystal systems are similar, the integrated intensity of each main peak is calculated by peak separation.)

[0084] Monoclinic ratio f m The monoclinic fraction f (%) is more preferably less than 50%, further preferably 48% or less, and particularly preferably 45% or less, from the viewpoint that the half width falls within a predetermined range and the resulting zirconia sintered body is excellent in mechanical strength and translucency. m (%) is preferably 5% or more, more preferably 10% or more, even more preferably 15% or more, and particularly preferably 20% or more.

[0085] The zirconia calcined body of the present invention may contain additives other than zirconia and stabilizers, such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (AlO), titanium oxide (TiO), and silica (SiO), as long as the effects of the present invention are achieved.

[0086] Examples of the pigment include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically, NiO, CrO, etc.) (however, YO and CeO are excluded). An oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb is preferred, and an oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb is more preferred. The zirconia calcined body of the present invention may also be free of erbium oxide (Er2O3). Examples of the composite pigment include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4.ZrSiO4, and (Co,Zn)Al2O4. Examples of the fluorescent agent include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl2O4. 10 O 17 : Eu, etc.

[0087] The zirconia calcined body of the present invention may contain a fluorescent agent. By including a fluorescent agent in the zirconia calcined body, the zirconia sintered body has fluorescence. The type of fluorescent agent is not particularly limited, and one or more fluorescent agents capable of emitting fluorescence with light of any wavelength can be used. Examples of fluorescent agents include those containing metal elements. Examples of such metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one of these metal elements alone, or two or more of them. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred. Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the above metal elements. The fluorescent agents are Y2SiO5:Ce, Y2SiO5:Tb, (Y, Gd, Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl.10 O 17 :Eu, etc.

[0088] The content of the fluorescent agent in the zirconia calcined body is not particularly limited and can be adjusted as appropriate depending on the type of fluorescent agent or the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the fluorescent agent content is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, calculated as the oxide of the metal element contained in the fluorescent agent, relative to 100% by mass of zirconia contained in the zirconia calcined body. Furthermore, the fluorescent agent content is not limited, as long as suitable fluorescence is exhibited, calculated as the oxide of the metal element contained in the fluorescent agent, but can be 1% by mass or less, 0.5% by mass or less, or even 0.1% by mass or less. When the content is equal to or greater than the lower limit, the fluorescence is comparable to that of natural human teeth. When the content is equal to or less than the upper limit, the decrease in mechanical strength and translucency can be suppressed.

[0089] The flexural strength of the zirconia calcined body of the present invention is preferably 15 MPa or more to ensure strength that allows mechanical processing in the calcined body state, and is preferably 70 MPa or less, more preferably 60 MPa or less, to facilitate mechanical processing in the calcined body state.

[0090] The bending strength can be measured in accordance with ISO 6872:2015 (Dentistry - Ceramic materials), but the only change is the size of the test specimen, which is measured using a test specimen measuring 5 mm x 10 mm x 50 mm. The test specimen's face and C-face (the surface where the corners of the test specimen are chamfered at a 45° angle) are finished in the longitudinal direction with 600-grit sandpaper. The test specimen is positioned so that the widest surface faces vertically (load direction). In the three-point bending test, the support distance (span) is 30 mm and the crosshead speed is 0.5 mm / min.

[0091] The density of the zirconia calcined body of the present invention is 2.7 g / cm 3More preferably, 3.0 g / cm 3 More preferably, it is 3.2 g / cm or more. 3 It is more preferable that the density of the zirconia calcined body is 4.0 g / cm or more. 3 Preferably, 3.8 g / cm or less 3 More preferably, 3.6 g / cm 3 The following is even more preferable: When the density is within the above range, molding can be easily carried out.

[0092] The density of the zirconia calcined body can be calculated by (mass of the zirconia calcined body) / (volume of the zirconia calcined body). The density of the zirconia calcined body can be calculated, for example, by cutting out 10 mm square specimens (n=3) from arbitrary positions on the zirconia calcined body while changing the cutting position, measuring the mass and volume of the obtained specimens, calculating the arithmetic mean value of the measured values, and using the arithmetic mean value to calculate the density according to the above formula.

[0093] [Zirconia Sintered Body] Next, the zirconia sintered body will be described. The zirconia sintered body is obtained by firing the zirconia calcined body obtained as described above.

[0094] The content of the stabilizer (preferably yttria) in the zirconia sintered body of the present invention is the same as the content of the stabilizer in the zirconia calcined body.

[0095] The zirconia sintered body of the present invention uses, as a raw material, small particles in which the concentration of the stabilizer is adjusted within a desired range. Therefore, even in a zirconia sintered body produced by firing at a maximum sintering temperature (e.g., 1550°C) for a retention time (holding time) of 10 minutes or less, the zirconia sintered body is excellent in the effect of controlling the opalescence within an appropriate range.

[0096] The zirconia sintered body of the present invention may contain a fluorescent agent. The fluorescent agent is the same as the fluorescent agent in the zirconia calcined body. In this specification, regarding the fluorescent agent, "relative to 100% by mass of zirconia contained in the zirconia calcined body" can be read as "relative to 100% by mass of zirconia contained in the zirconia sintered body."

[0097] The zirconia sintered body of the present invention may contain a colorant. Examples of colorants include those similar to those in the zirconia calcined body. The content of the colorant in the zirconia sintered body is not particularly limited and can be adjusted appropriately depending on the type of colorant and the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the content of the colorant, calculated as the oxide of the metal element contained in the colorant, relative to 100% by mass of zirconia contained in the zirconia sintered body, is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more. Furthermore, the content of the colorant, calculated as the oxide of the metal element contained in the colorant, is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and may even be 0.1% by mass or less, or even 0.05% by mass or less.

[0098] In order to adjust the translucency of the zirconia sintered body of the present invention, the zirconia sintered body of the present invention may contain a translucency adjuster. Examples of the translucency adjuster include the same ones as the translucency adjuster in the zirconia calcined body. The content of the translucency adjuster in the zirconia sintered body is not particularly limited and can be appropriately adjusted depending on the type of translucency adjuster and the application of the zirconia sintered body, but from the viewpoint of being preferably usable as a dental prosthesis, the content is preferably 0.1 mass% or less relative to 100 mass% of zirconia contained in the zirconia sintered body.

[0099] [Method for producing zirconia sintered body] Examples of methods for producing the zirconia sintered body of the present invention include methods for producing a zirconia sintered body by firing the above-mentioned zirconia calcined body. A preferred method includes a step of firing the above-mentioned zirconia calcined body at a maximum sintering temperature of more than 1200°C and not more than 1650°C under normal pressure (hereinafter also referred to as the "firing step"). In a preferred embodiment, the zirconia calcined body of the present invention contains small particles having a stabilizer concentration adjusted to a desired range, thereby making it possible to easily produce a zirconia sintered body of the present invention that has excellent translucency even after sintering for a short period of time, for example, a holding time of 10 minutes or less at the maximum sintering temperature.

[0100] When the zirconia calcined body of the present invention is fired to produce a sintered body, the maximum sintering temperature is preferably set to a value that maximizes the translucency of the zirconia sintered body. From the above perspective, the maximum sintering temperature is preferably greater than 1200°C, more preferably greater than 1250°C, and even more preferably greater than 1300°C, from the viewpoint of easily obtaining the desired zirconia sintered body under normal pressure. Furthermore, the maximum sintering temperature is preferably 1650°C or less, more preferably 1600°C or less, even more preferably 1550°C or less, particularly preferably 1500°C or less, and most preferably 1450°C or less. An embodiment of the present invention is a method for producing a zirconia sintered body, including a firing step in which the maximum sintering temperature is greater than 1200°C and less than 1450°C. By setting the maximum sintering temperature at or above the lower limit and at or below the upper limit, sintering can proceed sufficiently, making it easy to obtain a dense sintered body. Furthermore, by setting the maximum sintering temperature at or below the upper limit, deactivation of the fluorescent agent can be suppressed.

[0101] The holding time at the maximum sintering temperature is preferably 15 minutes or more, more preferably 30 minutes or more, and even more preferably 40 minutes or more. It is also preferably 20 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less. When producing a sintered body by sintering in a short period of time, there is no particular limitation on the sintering time as long as the holding time at the maximum sintering temperature is 10 minutes or less. However, since the desired zirconia sintered body can be obtained efficiently and stably with good productivity, the holding time at the maximum sintering temperature is preferably 10 minutes or less, more preferably 5 minutes or less, even more preferably 3 minutes or less, and particularly preferably 2 minutes or less. The holding time can be 30 seconds or more, 45 seconds or more, or even 1 minute or more.

[0102] When producing a sintered body, the firing time for producing the sintered body can be shortened without reducing the translucency of the zirconia sintered body. In particular, the holding time at the maximum sintering temperature for producing the sintered body can be shortened to 10 minutes or less. This improves production efficiency, and when the zirconia calcined body of the present invention is used for a dental product, it shortens the time from determining the dimensions of the dental product to be used for treatment, cutting the product, and preparing the dental product for treatment, thereby reducing the time burden on patients. It also reduces energy costs.

[0103] The temperature increase rate and temperature decrease rate in the firing step are preferably set so as to shorten the time required for the firing step. For example, the temperature increase rate can be set so as to reach the maximum sintering temperature in the shortest time depending on the performance of the firing furnace. The temperature increase rate to the maximum sintering temperature can be, for example, 10°C / min or more, 50°C / min or more, 100°C / min or more, 120°C / min or more, 150°C / min or more, 200°C / min or more, 250°C / min or more, 300°C / min or more, or 350°C / min or more. The temperature decrease rate is preferably set so as not to cause defects such as cracks in the sintered body. For example, after heating is completed, the sintered body can be allowed to cool at room temperature.

[0104] The calcination and firing in the present invention can be carried out using a firing furnace. There are no particular limitations on the type of firing furnace, and for example, electric furnaces and degreasing furnaces commonly used in industry can be used. A commercially available dental firing furnace (for example, the trade name "Sintra CS" (manufactured by Shenpaz)) can also be used.

[0105] The zirconia sintered body of the present invention can be produced without HIP treatment, but by optionally performing HIP treatment after sintering under normal pressure, it is possible to further improve translucency and mechanical strength. Hereinafter, the sintered body obtained by sintering at the above-mentioned maximum sintering temperature (the sintered body before HIP treatment) will be referred to as the "primary sintered body," and the sintered body after HIP treatment will be referred to as the "HIP-treated sintered body." HIP treatment can be performed using a known hot isostatic pressing (HIP) device.

[0106] When the primary sintered body is subjected to HIP treatment, the HIP pressure is not particularly limited, and since a dense sintered body with high mechanical strength can be obtained, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more. The upper limit of the HIP pressure is not particularly limited, but can be, for example, 400 MPa or less, 300 MPa or less, or even 200 MPa or less.

[0107] When the primary sintered body is subjected to HIP treatment, the temperature rise rate is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more. The temperature rise rate is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. By setting the temperature rise rate at or above the lower limit, productivity is improved.

[0108] When the primary sintered body is subjected to the HIP treatment, the HIP time is not particularly limited, and since a dense zirconia sintered body with high mechanical strength can be obtained, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Moreover, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0109] In the method for producing a zirconia sintered body of the present invention, the pressure medium used in HIPing the primary sintered body is not particularly limited. From the viewpoint of minimizing the effect on zirconia, the pressure medium can be at least one selected from the group consisting of oxygen, oxygen containing 3% hydrogen, air, and an inert gas (e.g., nitrogen, argon, etc.). When the primary sintered body is HIPed in an oxygen-mixed gas atmosphere, the oxygen concentration is not particularly limited, but can be, for example, more than 0% and 20% or less. When an oxygen-mixed gas is used, at least one inert gas (e.g., nitrogen, argon, etc.) can be selected as the gas other than oxygen.

[0110] If the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, black discoloration may occur due to oxygen defects. In this case, to remove the black discoloration, it is preferable to include a heat treatment step (hereinafter also referred to as a "tempering treatment") in the air or in an oxygen-excess atmosphere at 1650°C or less after the HIP treatment. From the viewpoint of efficient heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere. An oxygen-excess atmosphere means that the oxygen concentration is higher than that of the air. The oxygen-excess atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and 100% or less, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%. If the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, black discoloration may occur due to oxygen defects. In this case, to remove the black discoloration, it is preferable to include a heat treatment step (hereinafter also referred to as a "tempering treatment") in the air or in an oxygen-excess atmosphere at 1650°C or less after the HIP treatment. From the viewpoint of efficient heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere. An oxygen-excess atmosphere means that the oxygen concentration is higher than that of the air. The oxygen-excess atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and not more than 100%, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%.

[0111] The zirconia sintered body of the present invention is not particularly limited as long as it exhibits the effects of the present invention, and may be a primary sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment.

[0112] The temperature of the heat treatment in the air or in an oxygen-excess atmosphere can be appropriately changed depending on the aesthetics of the zirconia sintered body (e.g., the shade of a dental prosthesis). In a preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1650°C or less, more preferably 1600°C or less, and even more preferably 1550°C or less, from the viewpoint of the aesthetics of the zirconia sintered body. In another preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1400°C or less, more preferably 1300°C or less, and even more preferably 1200°C or less, from the viewpoint of the aesthetics of the zirconia sintered body. Furthermore, in any embodiment, the temperature of the heat treatment is preferably 500°C or more, more preferably 600°C or more, and even more preferably 700°C or more.

[0113] A general dental zirconia firing furnace can be used for the tempering treatment. Commercially available dental zirconia firing furnaces may be used. Examples of commercially available dental zirconia firing furnaces include Noritake Katana (registered trademark) F-1, F-1N, F-2, and F-2N (all manufactured by SK Medical Electronics Co., Ltd.).

[0114] The zirconia sintered body obtained by firing the zirconia calcined body of the present invention can be suitably used for dental products. Examples of dental products include copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, orthodontic wires, and laminate veneers. By using the zirconia calcined body of the present invention for parts such as implant screws and implant fixtures, discoloration of the gums caused by metals can be suppressed, resulting in excellent aesthetics. Furthermore, while an appropriate method can be selected for the manufacturing method of these products depending on the application, dental products can be obtained, for example, by cutting the zirconia calcined body of the present invention and then firing it. It is preferable to use a CAD / CAM system for the cutting process. The CAD / CAM system is not particularly limited, and known devices can be used. An example of a known device is a CAD / CAM system ("Katana (registered trademark) CAD / CAM system", manufactured by Kuraray Noritake Dental Co., Ltd.).

[0115] The present invention includes embodiments in which all or part of the above-described configurations are combined in various ways within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved.

[0116] Next, the present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way, and many modifications within the technical scope of the present invention are possible by those skilled in the art.

[0117] Example 1 Commercially available monoclinic zirconia powder (YO: 0 mol%) and commercially available yttria powder were added to water to give a concentration of 20 to 30 mass% (yttria content (ratio of moles of yttria to the total moles of zirconia and yttria): 4.5 mol%). These and zirconia grinding media (diameter: 0.1 mm) were placed in the container of a bead mill and ground in the bead mill for 1 hour to obtain a slurry.

[0118] The resulting slurry was then dried in a dryer at 85° C. The dried powder obtained by removing the water was added to ethanol in a sample bottle so as to have a concentration of about 0.1% by mass, and subjected to ultrasonic dispersion treatment for 2 to 30 minutes to obtain an ethanol solvent-diluted slurry containing a zirconia composition.

[0119] <TEM Observation of Zirconia Composition> One to two drops of the prepared ethanol solvent diluted slurry were placed on a microgrid for TEM measurement (product name "NP-M10-25" or "Microgrid Mo100P", equivalent to 250 mesh, manufactured by STEM Corporation) and dried. After confirming using an optical microscope that the powder was mounted on the grid, measurements were performed using a TEM (product name "JEM-ARM200F ACCELARM Atomic Resolution Analytical Electron Microscope", manufactured by JEOL Ltd.) at an accelerating voltage of 200 kV and a magnification of 200,000 or 1,500,000. The magnification can be adjusted appropriately depending on the particle diameter of the object to be observed.

[0120] <Method for Identifying Zirconia Particles> Zirconia particles (zirconia concentration of 80% by mass or more) were identified by the following method. When measured in a bright field at a high magnification (200,000 times) in TEM observation, particles with approximately constant brightness that included an observation point (observation area of ​​5 × 5 nm) where the zirconia concentration was 80% by mass or more in scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS) were regarded as a single zirconia particle. Alternatively, particles with increased brightness were regarded as a single zirconia particle when irradiated in a dark field at an accelerating voltage at which the diffraction pattern of monoclinic zirconia became clear.

[0121] <Method for measuring average primary particle diameter of zirconia particles> The circle-equivalent diameter (area-equivalent circle diameter) of each particle identified by the above-described method for identifying zirconia particles was defined as the primary particle diameter of each particle, and the average value of the circle-equivalent diameters of 10 particles arbitrarily selected in one visual field at a magnification of 200,000 times was defined as the average primary particle diameter of zirconia particles.

[0122] <Method for distinguishing small particles> Small particles were distinguished by the following method: When measuring at an ultra-high magnification (1.5 million times) in a bright field in TEM observation using the TEM used in the above <TEM observation of zirconia composition>, particles smaller than the average primary particle size of the zirconia particles were observed. When focusing on one particle, the points where the lattice fringes of the particle were interrupted (or switched) by visual observation were identified as grain boundaries, and these were regarded as one small particle.

[0123] <Method for measuring primary particle diameter and average primary particle diameter of small particles> The circle-equivalent diameter (area-equivalent circle diameter) of each particle identified by the above-described small particle identification method was taken as the primary particle diameter of each particle, and the average value of the circle-equivalent diameters of 10 particles arbitrarily selected in one visual field at a magnification of 200,000 times was taken as the average primary particle diameter of the small particles.

[0124] <Method for measuring yttria concentration in small particles> The yttria concentration of each small particle identified by the above-described method for identifying small particles was measured using STEM-EDS (observation area 5 × 5 nm). In Example 1, when 10 small particles were randomly selected from one field of view at a magnification of 200,000 times, the yttria concentration of all 10 of the 10 small particles was within the range of 10 to 50 mass %.

[0125] <Method for measuring the area ratio of zirconia particles to small particles> The area ratio (%) of zirconia particles to small particles was calculated using the area of ​​10 zirconia particles randomly selected from the plurality of particles identified by the above-described method for distinguishing zirconia particles and small particles, and the area of ​​10 small particles randomly selected in one field of view at a magnification of 200,000 times.

[0126] An organic binder was added to the ethanol solvent-diluted slurry obtained as described above, and the mixture was mixed and stirred. The stirred slurry was dried and granulated using a spray dryer to obtain a powder. This powder was poured into a cylindrical mold, uniaxially pressed at a pressure of 33 MPa, and then further subjected to CIP treatment at 190 MPa to obtain a plate- or disk-shaped compact. The obtained compact was placed in an electric furnace, heated from room temperature at a rate of 10°C / min, and held at 500°C for 2 hours to degrease the organic components. Thereafter, the temperature was raised at a rate of 10°C / min, held at 875°C for 2 hours, and slowly cooled at a rate of -10°C / min to obtain a zirconia calcined body.

[0127] This zirconia calcined body was then fired under atmospheric pressure at a temperature increase rate of 10°C / min at a maximum sintering temperature of 1,375°C for a holding time of 2 hours to obtain a zirconia sintered body containing 4.5 mol% of yttria. The resulting zirconia sintered body was white.

[0128] Comparative Example 1 A zirconia calcined body and a zirconia sintered body according to Comparative Example 1 were produced in the same manner as in Example 1, except that a ball mill (diameter: 2 mm) was used instead of the bead mill for the pulverization treatment and the pulverization treatment time was changed to 20 hours.

[0129] <Three-point bending strength> The three-point bending strength of the zirconia sintered body was measured in accordance with ISO 6872: 2015. A sample of 4 mm × 1.2 mm × 15 mm was prepared from the plate-shaped zirconia sintered body of each Example and Comparative Example, and the sample was measured using a universal testing machine under the conditions of a support distance of 12 mm and a crosshead speed of 0.5 mm / min.

[0130] <Opality (OP value) of zirconia sintered body> The OP value of the zirconia sintered body was measured using a spectrophotometer ("CM-3610A" manufactured by Konica Minolta Japan Inc.). * 透過 , a * 反射 , b * 透過 , b * 反射 was measured and calculated using the following formula. In this measurement, an F11 light source was used, and the reflected light was measured. For the measurement, a disk-shaped zirconia sintered body with a diameter of 15 mm and a thickness of 1.0 mm obtained by mirror polishing both sides was used as a sample, and the average value measured with n = 3 was calculated. An OP value of 4.5 or more and 9.0 or less was considered to be acceptable.

[0131] In the table, the yttria content of the sintered body was 4.5 mol% in Example 1 and Comparative Example 1. The zirconia concentration (mass%) in the small particles can be calculated using the yttria concentration in the small particles in Table 1 by subtracting the yttria concentration (mass%) from 100 (mass%).

[0132] From the above results, it was confirmed that the zirconia calcined body of the present invention provides a zirconia sintered body having excellent mechanical strength and an excellent effect of controlling opalescence within an appropriate range. In Comparative Example 1, the zirconia composition did not contain small particles and had a stabilizer concentration of 10 to 50 mass %, so the opalescence could not be controlled within an appropriate range, and the desired physical properties were not obtained.

[0133] The zirconia compositions of the present invention are useful for manufacturing dental products, particularly for manufacturing dental products for dental clinic treatment.

Claims

1. Zirconia particles with a zirconia concentration of 80% by mass or more, The small particles contain a stabilizer capable of suppressing the phase transition of zirconia, with a concentration of 10 to 50% by mass. A zirconia composition in which the small particles have an average primary particle diameter smaller than the average primary particle diameter of the zirconia particles.

2. The zirconia composition according to claim 1, wherein, under TEM observation, 10 small particles are arbitrarily selected, and 6 or more of the 10 small particles are small particles in which the concentration of the stabilizer is 10 to 50% by mass.

3. The zirconia composition according to claim 1 or 2, wherein the average primary particle diameter of the zirconia particles is 0.06 to 0.17 μm.

4. The zirconia composition according to claim 1 or 2, wherein the average primary particle diameter of the small particles is less than 0.06 μm.

5. The zirconia composition according to claim 1 or 2, wherein the stabilizer capable of suppressing the phase transition of the zirconia is yttria.

6. The zirconia composition according to claim 1 or 2, wherein, under TEM observation, the area ratio of the zirconia particles to the small particles is 55 / 45 to 99 / 1.

7. A process for manufacturing a raw material composition comprising zirconia particles and stabilizer particles capable of suppressing the phase transition of zirconia, The process includes a grinding step of grinding the raw material composition, A method for producing a zirconia composition according to claim 1 or 2, wherein the grinding step uses grinding media with a diameter of less than 1 mm.

8. A method for producing a zirconia composition according to claim 7, wherein the processing time for the grinding step is 20 minutes to 2 hours.

9. A method for producing a zirconia composition according to claim 7, wherein the average primary particle diameter of the zirconia particles is 0.06 to 0.17 μm.

10. A method for producing a zirconia composition according to claim 7, wherein the average primary particle diameter of the small particles is less than 0.06 μm.

11. The method for producing a zirconia composition according to claim 7, wherein the stabilizer capable of suppressing the phase transition of the zirconia is yttria.

12. A method for producing a zirconia composition according to claim 7, further comprising the steps of producing a slurry containing the zirconia composition and spray-drying it to granulate it.