Zirconia composition and method for producing same

Abstract

Provided are: a zirconia composition in which the mechanical strength of a zirconia sintered body obtained is excellent, and opalescence can be controlled to an appropriate range; and a method for producing the zirconia composition. The present invention relates to a zirconia composition comprising zirconia particles in which the concentration of zirconia is 80% by mass or more and small particles in which the concentration of a stabilizer capable of suppressing the phase change of zirconia is 10-50% by mass, the small particles having a primary particle diameter smaller than the average primary particle diameter of the zirconia particles.

Description

Technical Field

[0001] This invention relates to zirconia compositions and methods for manufacturing the same. More specifically, this invention relates to zirconia compositions and methods for manufacturing the same, resulting in sintered zirconia bodies with excellent mechanical strength and controllable opalescence within an appropriate range. Background Technology

[0002] Zirconia sintered bodies are widely used in industry, and in recent years they have been used in dental materials such as dental repairs. These dental repairs are typically manufactured by pressing zirconia particles or molding them using a composition containing zirconia particles to create a zirconia molded body with a desired shape, such as a disc or prism. This molded body is then pre-fired to create a pre-fired body (grind blank), which is then cut (ground) into the shape of the desired dental repair. Finally, it is further calcined.

[0003] Zirconia is a compound that undergoes phase transitions between multiple crystal systems. Therefore, partially-stabilized zirconia (PSZ) and fully-stabilized zirconia (FSZ) are used in various fields to suppress phase transitions by dissolving stabilizers such as yttrium oxide (Y₂O₃) in zirconia.

[0004] In dentistry, zirconia, while possessing high strength, has low light transmittance, thus it is primarily used for framing. Furthermore, in recent years, with the improvement in the light transmittance of zirconia, it has become increasingly common to use zirconia alone to fabricate dental restorations.

[0005] Examples of dental materials that use such zirconia include, for example, Patent Document 1.

[0006] Existing technical documents Patent documents Patent Document 1: International Publication No. 2022 / 138881. Summary of the Invention

[0007] The problem the invention aims to solve However, the zirconia sintered body obtained by using the zirconia pre-burned body involved in Patent Document 1, when simply keeping the crystalline structure small, will appear colored due to the selective reflection or transmission of specific wavelengths by its uniform structure, which is called structural color (hereinafter referred to as "opalescent"). From this point of view, there is room for improvement from the perspective of having an appearance with a tone closer to that of natural teeth.

[0008] The purpose of this invention is to provide a zirconia composition with excellent mechanical strength and a method for manufacturing the same, which allows for control of opalescence within an appropriate range in the obtained zirconia sintered body.

[0009] means for solving problems To solve the aforementioned problems, the inventors conducted in-depth research and discovered that by preparing a zirconium composition comprising zirconium oxide particles at a concentration of 80% by mass or more, and small particles containing a stabilizer capable of suppressing the phase transformation of zirconium oxide at a concentration of 10-50% by mass, wherein the small particles have a primary particle size smaller than the average primary particle size of the zirconium oxide particles, the resulting zirconium sintered body exhibits excellent mechanical strength and its opalescence can be controlled within an appropriate range. Based on this insight, further research was conducted, leading to the completion of this invention.

[0010] This invention includes the following inventions.

[0011] [1] A zirconium oxide composition comprising zirconium oxide particles having a zirconium oxide concentration of 80% by mass or more, and Small particles containing 10-50% by mass of stabilizers capable of suppressing the phase transformation of zirconium oxide. The aforementioned small particles have a primary particle size smaller than the average primary particle size of the aforementioned zirconia particles.

[0012] [2] According to the zirconium oxide composition of [1], under TEM observation, arbitrarily select 10 small particles, of which 6 or more of the 10 small particles are small particles with a concentration of the stabilizer of 10 to 50% by mass.

[0013] [3] The zirconium oxide composition according to [1] or [2], wherein the average primary particle size of the aforementioned zirconium oxide particles is 0.06 to 0.17 μm.

[0014] [4] The zirconium oxide composition according to any one of [1] to [3], wherein the average primary particle size of the aforementioned small particles is less than 0.06 μm.

[0015] [5] The zirconium oxide composition according to any one of [1] to [4], wherein the aforementioned stabilizer capable of suppressing the phase transformation of zirconium oxide is yttrium oxide.

[0016] [6] The zirconium oxide composition according to any one of [1] to [5], wherein, under TEM observation, the area ratio of the zirconium oxide particles to the small particles is 55 / 45 to 99 / 1.

[0017] A method for manufacturing a zirconium oxide composition as described in any one of [7][1] to [6], comprising: a step of manufacturing a raw material composition comprising zirconium oxide particles and particles of a stabilizer capable of inhibiting the phase transformation of zirconium oxide; and The pulverization process of pulverizing the aforementioned zirconium oxide composition. The aforementioned crushing process uses crushing media with a diameter of less than 1 mm.

[0018] [8] In the method for manufacturing the zirconium oxide composition according to [7], the processing time of the aforementioned pulverizing step is 20 minutes to 2 hours.

[0019] [9] The method for manufacturing the zirconium oxide composition according to [7] or [8], wherein the average primary particle size of the aforementioned zirconium oxide particles is 0.06 to 0.17 μm.

[0020]

[10] The method for manufacturing the zirconium oxide composition according to any one of [7] to [9], wherein the average primary particle size of the aforementioned small particles is less than 0.06 μm.

[0021]

[11] The method for manufacturing a zirconium oxide composition according to any one of [7] to

[10] , wherein the aforementioned stabilizer capable of suppressing the phase transformation of zirconium oxide is yttrium oxide.

[0022]

[12] The method for manufacturing the zirconium oxide composition according to any one of [7] to

[11] further includes the steps of manufacturing a slurry containing the aforementioned raw material composition and spray drying to granulate it.

[0023] Invention Effects According to the present invention, a zirconia composition with excellent mechanical strength and a method for manufacturing the same can be provided, wherein the resulting zirconia sintered body has opalescence controlled to an appropriate range.

[0024] Furthermore, by using the zirconia pre-sintered body of the present invention, a zirconia sintered body with excellent mechanical strength and light transmittance can be obtained at a lower maximum sintering temperature than before (e.g., below 1450°C).

[0025] Furthermore, by using the zirconia pre-sintered body of the present invention, a zirconia sintered body with excellent mechanical strength and light transmittance can be provided without the use of a HIP device. Detailed Implementation

[0026] [Zirconium oxide composition] The zirconia composition of the present invention comprises zirconia particles having a zirconia concentration of 80% by mass or more, and Small particles (hereinafter referred to as "small particles") containing a concentration of 10-50% by mass of stabilizer capable of suppressing the phase transformation of zirconium oxide. The aforementioned small particles have a primary particle size smaller than the average primary particle size of the aforementioned zirconia particles.

[0027] In this specification, "zirconia composition" refers to a composition containing zirconia powder and stabilizer powder.

[0028] In this specification, "molded body" refers to an object that has not reached the semi-sintered state (pre-sintered state) or the sintered state. That is, the molded body is distinguished from the pre-sintered body and the sintered body in that it has not been calcined after being formed by molding.

[0029] In this specification, "zirconia pre-sintered body" refers to a semi-sintered object in which zirconia particles are necked (fixed) together and are not fully sintered.

[0030] In this specification, "zirconia sintered body" refers to an object in a sintered state where zirconia particles are completely sintered. In a zirconia sintered body, the zirconia particles are bonded together by sintering, and as sintering progresses, the relative density increases, resulting in densification. Therefore, it exhibits a fully sintered state with a relative density of over 95%.

[0031] In this specification, "zirconia" refers to zirconia (IV) (ZrO2), where ZrO2 particles contain trace amounts (more than 0.5% by mass and less than 3% by mass) of HfO2 relative to the amount of ZrO2. HfO2 is difficult to separate; therefore, terms such as "zirconia," "zirconia particles," and "zirconia powder" refer to substances containing both ZrO2 and HfO2. Furthermore, particles and / or powders of stabilizers dissolved in zirconia are also included in "zirconia particles" and "zirconia powder," respectively.

[0032] In this instruction manual, "atmospheric pressure" refers to standard atmospheric pressure (1 atm).

[0033] It should be noted that the upper and lower limits of the numerical ranges (temperature range, content of each component, presence rate of crystal system, values ​​calculated from components, and various physical properties, etc.) in this specification can be appropriately combined.

[0034] The zirconia sintered body obtained by having a concentration of 10-50% by mass of a stabilizer in the small particles contained together with the zirconia particles in the zirconia composition of the present invention exhibits excellent mechanical strength and can control opalescence to an appropriate range. The reason for this is not yet determined, but is speculated as follows.

[0035] In zirconia compositions, by including small particles of a stabilizer at a concentration of 10–50% by mass, which can suppress the phase transformation of zirconia, along with the zirconia particles, it is possible to improve the imbalance of stabilizer in zirconia compositions, which was not achievable in conventional unsolvable zirconia (zirconia in which the stabilizer is not dissolved). As a result, it can be considered that the obtained sintered body, with a relatively uniform sintered structure in terms of crystal grain size and composition, can achieve a sintered body with excellent mechanical strength and opalescence controlled within an appropriate range.

[0036] [Method for manufacturing zirconium oxide composition] The zirconia composition of the present invention can be manufactured by providing an excess of energy compared with the prior art by pulverizing a raw zirconia composition (hereinafter also referred to as "raw material composition" or "zirconia composition before pulverization") containing zirconia particles and particles of a stabilizer capable of inhibiting the zirconia phase transformation (hereinafter also simply referred to as "stabilizer") under specified conditions.

[0037] Stabilizers (hereinafter also referred to as "stabilizers") that can suppress the phase transformation of zirconium oxide include, for example, 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 (Pr2O3, Pr6O3). 11 Oxides such as samarium oxide (Sm₂O₃), europium oxide (Eu₂O₃), thulium oxide (Tm₂O₃), gallium oxide (Ga₂O₃), indium oxide (In₂O₃), and yttrium oxide (Yb₂O₃) are preferred. One of the aforementioned stabilizers may be used alone, or two or more may be used in combination.

[0038] In the zirconium oxide composition of the present invention, the stabilizer may be only yttrium oxide (Y2O3), or may further include yttrium oxide and other stabilizers capable of inhibiting the phase transformation of zirconium oxide besides yttrium oxide.

[0039] The content of stabilizer in the zirconium oxide 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, relative to the total molar content of zirconium oxide and stabilizer. From the viewpoint that 2.5 mol% or more increases the cubic crystal system within the sintered body and improves light transmittance, this is preferable.

[0040] Furthermore, the content of the aforementioned 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. From the viewpoint of preventing strength reduction, a content of 10 mol% or less is preferred.

[0041] The manufacturing method of the zirconium oxide composition will be illustrated by taking the case where the stabilizer is yttrium oxide as an example.

[0042] The zirconia composition (raw material composition) before pulverization can be prepared by mixing zirconia powder, which is used as a raw material powder, with yttrium oxide powder. The mixing method is not particularly limited, and known methods and apparatus can be used.

[0043] As a method for preparing zirconium oxide particles constituting zirconium oxide powder and yttrium oxide particles constituting yttrium oxide powder, a crushing process that achieves micronization by crushing or breaking down coarse particles can be adopted, for example, an aggregation process that synthesizes particles by atoms or ions through a nucleation and growth process. However, considering that a specific crushing process is required to adjust the concentration of stabilizer in small particles to the desired range when manufacturing by aggregation process, from the viewpoint of easy manufacturing, the crushing process is preferred.

[0044] The following describes the manufacturing method of the zirconium oxide composition, using the crushing process as an example.

[0045] The zirconium oxide constituting the aforementioned zirconium oxide powder preferably includes monoclinic zirconium oxide.

[0046] In one embodiment, the zirconia constituting the aforementioned zirconia powder may include monoclinic zirconia, and may further include tetragonal zirconia, and / or cubic zirconia.

[0047] In another embodiment, the zirconia constituting the aforementioned zirconia powder may include tetragonal zirconia and / or cubic zirconia, or may not include monoclinic zirconia.

[0048] In zirconium oxide powder, these crystal systems can be used individually or in combination of two or more.

[0049] Zirconia powder used as raw material powder can be commercially available zirconia particles, or it can be pulverized using a known pulverizing and mixing device (ball mill, etc.) before use.

[0050] Yttrium oxide powder, used as a raw material powder, can be commercially available yttrium oxide granules, or it can be pulverized using a known pulverizing and mixing device (ball mill, etc.) before use.

[0051] Commercially available zirconium oxide powders include, for example, those marketed under the trade names "Zpex (registered trademark)" (Y₂O₃ content: 3 mol%), "Zpex (registered trademark) 4" (Y₂O₃ content: 4 mol%), "Zpex (registered trademark) Smile (registered trademark)" (Y₂O₃ content: 5.5 mol%), "TZ-3Y" (Y₂O₃ content: 3 mol%), "TZ-3YS" (Y₂O₃ content: 3 mol%), "TZ-4YS" (Y₂O₃ content: 4 mol%), "TZ-6Y" (Y₂O₃ content: 6 mol%), "TZ-6YS" (Y₂O₃ content: 6 mol%), "TZ-8YS" (Y₂O₃ content: 8 mol%), and "TZ..." -10YS (Y2O3 content: 10 mol%), "TZ-3Y-E" (Y2O3 content: 3 mol%), "TZ-3YS-E" (Y2O3 content: 3 mol%), "TZ-3YB-E" (Y2O3 content: 3 mol%), "TZ-3YSB-E" (Y2O3 content: 3 mol%), "TZ-3YB" (Y2O3 content: 3 mol%), "TZ-3YSB" (Y2O3 content: 3 mol%), "TZ-3Y20AB" (Y2O3 content: 3 mol%), "TZ-8YSB" (Y2O3 content: 8 mol%), "TZ-0" (Y2O3 content: 0 mol%; monoclinic zirconia); all of the above are manufactured by Tosoh Corporation, etc.

[0052] Next, the zirconium oxide composition containing zirconium oxide particles and stabilizer particles is subjected to a pulverization process.

[0053] In a crushing process under specified conditions, by applying excessive energy compared to existing technologies, it is possible to obtain a zirconia composition containing small particles and zirconia particles with the concentration of stabilizer adjusted to a desired range.

[0054] Previously, regarding zirconia particles, since zirconia itself is a very hard material, it was difficult to excessively reduce the size of zirconia particles even if the energy value of the crushing process was increased. From this point of view, no technical significance was found in excessive crushing.

[0055] However, it can be inferred that when the zirconium oxide composition containing zirconium oxide and yttrium oxide is supplied to the pulverization process in this invention, by adjusting the concentration of the stabilizer in the small particles to the desired range, in the manufacture of sintered bodies, in addition to the excellent mechanical strength, the opalescence can also be controlled to an appropriate range, thus exhibiting excellent aesthetics.

[0056] By adjusting the concentration of stabilizer in the small particles to the desired range, in addition to the excellent mechanical strength of the final sintered body, the opalescence can also be controlled to an appropriate range. In order to exhibit excellent aesthetics, starting from applying excess energy to the zirconia composition, as a specific operation in the pulverization process, a pulverizing medium with a diameter of less than 1 mm is used.

[0057] This pulverization process involves disintegration and pulverization, thereby promoting mixing while micronizing the zirconium oxide and yttrium oxide particles. This allows the concentration of stabilizer in the small particles of the resulting zirconium oxide composition to be adjusted to the desired range.

[0058] Furthermore, during these pulverization processes, the solid solution and amorphization of yttrium oxide occur, and the presence rate of undissolved yttrium oxide can be adjusted using Equation (1-1). As long as the zirconia composition contains small particles of zirconia with the stabilizer concentration adjusted to the desired range, in addition to the excellent mechanical strength of the final sintered body, the opalescence can be controlled to an appropriate range; therefore, the presence rate of undissolved yttrium oxide is not particularly limited. The presence rate of undissolved yttrium oxide can be controlled by adjusting the pulverization time.

[0059] When using a grinding medium with a diameter of less than 1 mm, the diameter of the grinding medium is preferably 0.1 to 0.5 mm, from the viewpoint that it is easy to increase the energy value of the grinding process and easy to adjust the concentration of stabilizer in small particles to the desired range by using a grinding medium with a fine diameter.

[0060] Commercially available products can be used as pulverizing media with a diameter of less than 1 mm.

[0061] Examples of grinding devices that use grinding media with a diameter of less than 1 mm include bead mills.

[0062] When using a pulverizing medium with a diameter of less than 1 mm, the pulverization time is not particularly limited as long as a zirconia composition containing zirconia particles with a concentration of 80% by mass or more and a stabilizer concentration of 10-50% by mass is obtained. From the viewpoint of easily adjusting the concentration of stabilizer in the small particles to the desired range, 10 minutes or more is preferred, more preferably 15 minutes or more, further preferably 20 minutes or more, and particularly preferably 30 minutes or more. Furthermore, from the viewpoint of easily adjusting the concentration of stabilizer in the small particles to the desired range, the pulverization time is preferably 20 hours or less, more preferably 10 hours or less, further preferably 5 hours or less, and particularly preferably 2 hours or less.

[0063] It should be noted that when using a pulverizing device that circulates the slurry while pulverizing (such as a circulating bead mill) as a pulverizing device, the pulverizing time refers to the residence time of the slurry in the container (pulverizing chamber).

[0064] In this invention, by supplying the zirconia composition with pulverizing energy that is adjusted and increased according to the combination of pulverizing time and pulverizing media diameter, it is possible to obtain a zirconia composition containing small particles and zirconia particles with the concentration of stabilizer adjusted to a desired range.

[0065] It can be inferred that by using a zirconia composition containing small particles and zirconia particles with the concentration of the stabilizer obtained as described above adjusted to the desired range to produce a zirconia pre-sintered body, and then producing a zirconia sintered body, in addition to the excellent mechanical strength of the resulting sintered body, the opalescence can also be controlled to an appropriate range, thus exhibiting excellent aesthetics.

[0066] Because of its excellent mechanical strength and ease of controlling opalescence to an appropriate range, the concentration of stabilizer in the small particles contained in the pulverized zirconia composition is preferably 10% by mass or more, more preferably 10.5% by mass or more, further preferably 11% by mass or more, and particularly preferably 11.5% by mass or more. Furthermore, because of its excellent mechanical strength and ease of controlling opalescence to an appropriate range, the concentration of stabilizer in the small particles is preferably 50% by mass or less, more preferably 45% by mass or less, further preferably 40% by mass or less, and particularly preferably 35% by mass or less.

[0067] The pulverized zirconium oxide composition can also form a small particle cluster containing multiple small particles with the concentration of stabilizer adjusted to the desired range, provided that the opalescence is controlled to an appropriate range.

[0068] Among the above-mentioned small particle groups, the mechanical strength is excellent and the opalescence is easily controlled to an appropriate range. Therefore, the concentration of the stabilizer is preferably 10 to 50% by mass.

[0069] 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 zirconium oxide composition.

[0070] Furthermore, from the viewpoint that the concentration of zirconium oxide in the small particles is integrated with the concentration of the stabilizer, resulting in excellent mechanical strength and easy control of opalescence within an appropriate range, the concentration of zirconium oxide in the aforementioned small particle group is preferably 50% by mass or more, more preferably 55% by mass or more, further preferably 60% by mass or more, and particularly preferably 65% ​​by mass or more. Additionally, from the viewpoint that the concentration of zirconium oxide in the small particles is integrated with the concentration of the stabilizer, resulting in excellent mechanical strength and easy control of opalescence within an appropriate range, the concentration of zirconium oxide in the aforementioned small particle group is preferably 90% by mass or less, more preferably 89.5% by mass or less, further preferably 89% by mass or less, and particularly preferably 88.5% by mass or less.

[0071] From the viewpoint of having excellent mechanical strength and easily controlling opalescence to an appropriate range, the pulverized zirconium oxide composition preferably consists of 10 small particles randomly selected from 1 field of view with a magnification of 200,000x under transmission electron microscopy (TEM), wherein at least 6 of the aforementioned 10 small particles are small particles with a stabilizer concentration of 10 to 50% by mass.

[0072] Of the aforementioned 10 small particles, it is more preferable that there are 7 or more small particles with a stabilizer concentration of 10 to 50% by mass, further preferably 8 or more, particularly preferably 9 or more, and most preferably 10.

[0073] Additionally, if you cannot obtain 10 small particles from one field of view, you can increase the number of fields of view and select a total of 10 small particles.

[0074] Similarly, in this instruction manual, when selecting a specific number (e.g., 10) of small particles in a field of view, or when the target number of particles cannot be determined in a single field of view, the number of fields of view can be increased to two or more, and the target number (e.g., 10) can be selected in a total manner. For example, when selecting 100 particles, any 10 particles can be selected from four fields of view, and this process can be repeated until the target number of 100 is reached.

[0075] Furthermore, when arbitrarily selecting 10 small particles for observation under TEM and observing 10 fields of view respectively, it is preferable that the zirconia composition satisfies the above-mentioned number of small particles in 6 or more fields of view, more preferably that the zirconia composition satisfies the above-mentioned number of small particles in 8 or more fields of view, even more preferably that the zirconia composition satisfies the above-mentioned number of small particles in 9 or more fields of view, and particularly preferably that the zirconia composition satisfies the above-mentioned number of small particles in all 10 fields of view.

[0076] As a suitable embodiment, among 100 (e.g., any 10 × 10 fields of view in one field of view with a magnification of 200,000x), preferably 60 or more are small zirconia compositions in which the concentration of stabilizer is 10 to 50% by mass, more preferably 70 or more, further preferably 80 or more, particularly preferably 90 or more, and most preferably 100.

[0077] In this invention, the number of objects observed by TEM can be more than 200 or more than 500, depending on the needs.

[0078] From the viewpoint of having excellent mechanical strength and easily controlling opalescence to an appropriate range, the zirconia composition after pulverization, under TEM observation, has the following area ratio (%) as zirconia particles and small particles: zirconia particles / small particles preferably 55 / 45 to 99 / 1, more preferably 65 / 35 to 98 / 2, further preferably 70 / 30 to 97 / 3, and particularly preferably 75 / 25 to 95 / 5.

[0079] The zirconium oxide composition before and after pulverization can be in the form of particles, slurry, etc.

[0080] When the zirconium oxide composition is a slurry, the slurry can be manufactured by mixing the mixed powder obtained by pulverization with a solvent (suitably water).

[0081] In addition, the zirconia composition may contain additives such as binders, dispersants, emulsifiers, defoamers, pH adjusters, lubricants, and light transmittance adjusters. One additive may be used alone, or two or more may be used in combination.

[0082] Examples of adhesives include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic adhesives, wax adhesives, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.

[0083] To improve light transmittance, the binder content in the zirconium oxide composition of the present invention is preferably 10% by mass or less relative to 100% by mass of zirconium oxide, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0084] Examples of plasticizers include polyethylene glycol, glycerin, propylene glycol, and dibutylphthalic acid.

[0085] 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, glyceryl oleate, amine salt surfactants, oligosaccharide alcohols, stearic acid, etc.

[0086] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitol derivatives.

[0087] Examples of defoaming agents include alcohols, polyethers, polyethylene glycols, silicones, and waxes.

[0088] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxide such as tetramethylammonium hydroxide).

[0089] Examples of lubricants include polyoxyethylene alkyl ethers and waxes.

[0090] Examples of light transmittance modifiers include aluminum oxide (Al2O3), titanium dioxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0091] The BET specific surface area of ​​the particles constituting the zirconia composition, when measured according to JIS Z 8830:2013, is preferably 7.0 m². 2 / g or more, preferably 7.5m 2 / g or more, further preferably 8.0m 2 / g or more. At 7.0m 2 When the surface area is above a certain value (e.g.), it is easier to suppress the formation of white turbidity in the sintered body during sintering. Furthermore, the preferred BET specific surface area is 50 m² / g. 2 / g or less, preferably 45m 2 / g or less, more preferably 40m 2 / g or less. At 50m 2 When the content is below / g, it is not easily affected by uneven temperature inside the calcining furnace.

[0092] BET surface area can be measured using commercially available devices such as the fully automated surface area measuring device (trade name "Macsorb (registered trademark) HMmodel-1200", BET flow method (single-point method / multi-point method), manufactured by Mountech). For example, the aforementioned fully automated surface area measuring device can be used to perform the measurement using the BET flow method (single-point method).

[0093] Furthermore, the light transmittance of the sintered body is not easily reduced when the calcination time for sintering is shortened. The "BET specific surface area" mentioned here refers to the specific surface area measured without distinguishing between primary and secondary particles.

[0094] From the viewpoint that the sintered body has excellent mechanical strength and that the opalescence can be controlled to an appropriate range, the average particle size of the zirconia composition after pulverization is preferably 0.2 μm or less.

[0095] The average particle size of the zirconia and yttrium oxide particles in the pulverized zirconia composition can be determined by a dynamic light scattering particle size distribution measurement method. For example, a dynamic light scattering particle size distribution measurement device (trade name "SZ-100V2") manufactured by Horiba Corporation can be used to subject a slurry diluted with water to approximately 0.1% by mass to ultrasonic irradiation for 30 minutes, followed by measurement based on volume while in contact with ultrasonic waves.

[0096] The average primary particle size of the zirconia particles contained in the pulverized zirconia composition is preferably 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.06 μm or more. Furthermore, the average primary particle size of the aforementioned zirconia particles is preferably 0.20 μm or less, more preferably 0.19 μm or less, and even more preferably 0.17 μm or less.

[0097] The average primary particle size of the small particles contained in the pulverized zirconium oxide composition is preferably less than 0.06 μm, more preferably less than 0.05 μm, and even more preferably less than 0.04 μm.

[0098] Next, a molded body is produced by molding the pulverized zirconium oxide composition. The molded body is obtained by applying external force to the zirconium oxide composition and molding it using a known method.

[0099] There are no particular limitations on the molding method; for example, the following methods can be used.

[0100] (a) A process of casting a slurry containing a pulverized zirconium oxide composition; (b) A process of gel casting a slurry containing a pulverized zirconium oxide composition; (c) The process of pressing the pulverized zirconium oxide composition into shape; (d) A process for molding a zirconium oxide composition comprising zirconium oxide particles, small particles and resin; (e) A process of polymerizing a zirconium oxide composition comprising zirconium oxide particles, small particles, and containing polymerizable monomers and / or oligomers; and (f) Processes such as stacking and shaping particles containing zirconium oxide particles and small particles.

[0101] (a) Powder slurry pouring When manufacturing a zirconia molded body using a method that involves casting a slurry containing a pulverized zirconia composition, the specific method of casting the slurry is not particularly limited, and methods such as drying the slurry after it has been poured into a mold can be employed.

[0102] From the perspective 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 is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less.

[0103] The slurry can be poured into the mold under normal pressure, but from the point of view of production efficiency, it is preferable to do so under pressure.

[0104] (b) Gel casting When manufacturing a zirconia molded body by means of a process of gel casting a slurry containing a pulverized zirconia composition, the specific method of gel casting is not particularly limited. For example, a method can be used to obtain a shaped wet body by gelling the aforementioned slurry in a mold and then drying it.

[0105] From the perspective of preventing excessive drying time and suppressing cracks during drying, 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.

[0106] Gelation can be achieved, for example, by adding a gelling agent, or by polymerizing a polymerizable monomer after its addition.

[0107] There are no restrictions on the type of gelling agent; water-soluble gelling agents can be used, with agarose and gelatin being preferred. A single gelling agent can be used, or two or more can be used in combination. The amount of gelling agent used is not particularly limited as long as it does not cause problems such as cracking during sintering. Depending on the mass of the slurry after mixing the gelling agent, it can be set to less than 10% by mass, less than 5% by mass, or less than 1% by mass.

[0108] Furthermore, there are no particular limitations on the types of polymerizable monomers. 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, and other (meth)acrylate monomers; N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N,N-bis(2-hydroxyethyl)(meth)acrylamide, and other (meth)acrylamide monomers. A single polymerizable monomer can be used, or two or more monomers can be used in combination.

[0109] There is no particular limit to the amount of polymerizable monomers used, as long as problems such as cracking during sintering do not occur. Depending on the quality of the slurry after mixing the polymerizable monomers, it can be set to less than 10% by mass, less than 5% by mass, or less than 1% by mass.

[0110] When gelation is achieved by polymerization of polymerizable monomers, a polymerization initiator is preferably used. The type of polymerization initiator is not particularly limited, but photopolymerization initiators are particularly preferred. As a photopolymerization initiator, a suitable selection can be made from photopolymerization initiators commonly used in industry, with photopolymerization initiators used in dental applications being preferred.

[0111] 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 alone, 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. 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, light-emitting diodes (LEDs), mercury lamps, and fluorescent lamps.

[0112] 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 may be used. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred in order to suppress the formation of cracks during drying.

[0113] There are no particular limitations on the types of molds used in slurry casting and gel casting. For example, porous molds made of plaster, resin, ceramics, etc., and non-porous molds made of metal, resin, etc., can be used.

[0114] (c) Pressure molding In the process of press molding the pulverized zirconium oxide composition, there is no particular limitation on the specific method of press molding, and a known press molding machine can be used.

[0115] Specific methods of pressure molding include, for example, uniaxial pressure molding.

[0116] In addition, multi-stage molding can be performed. For example, after the zirconia composition is press-molded, it can be further subjected to CIP (Cold Isostatic Pressing) treatment.

[0117] The shape of the aforementioned molded body is not particularly limited and can be disc-shaped, cuboid-shaped, or in the shape of a dental product (e.g., a crown).

[0118] The molded body can be, for example, a columnar zirconia molded body in which a zirconia composition (e.g., particles) is filled into a mold and compacted by uniaxial pressure.

[0119] The higher the surface pressure during pressure 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 pre-sintered body will harden. Therefore, the surface pressure during pressure molding of zirconia molded bodies is preferably 30~200 MPa. When the surface pressure is 30 MPa or higher, the shape retention of the zirconia molded body is excellent. In addition, when the pressure is below 200 MPa, the density of the zirconia molded body will not increase excessively, making it easier to prevent hardening.

[0120] The aforementioned molded articles also include those that have been densified by high-temperature pressure treatment, such as CIP (Cold Isostatic Pressing).

[0121] Based on the same viewpoint as mentioned above, the CIP pressure is preferably 30~200MPa.

[0122] (d) Molding of a zirconia composition containing resin When a zirconia molded body is manufactured by means of a step of molding a zirconia composition comprising zirconia particles, small particles and resin, the specific method used to mold the zirconia composition is not particularly limited, and can be, for example, injection molding, injection molding, extrusion molding, etc.

[0123] Alternatively, molding methods such as hot-melt dissolution (FDM), inkjet printing, and powder / binder lamination (3D printing, etc.) can be used. Among these molding methods, injection molding and injection molding are preferred, and injection molding is more preferred.

[0124] There is no particular limitation on the type of resin mentioned above, but the aforementioned adhesive is preferred.

[0125] (e) Polymerization of zirconium oxide compositions comprising zirconium oxide particles, small particles and containing polymerizable monomers and / or oligomers Curing can be achieved by polymerizing a zirconium oxide composition containing zirconium oxide particles, small particles, and polymerizable monomers and / or oligomers, thereby polymerizing the polymerizable monomers and / or oligomers in the composition.

[0126] When manufacturing zirconia molded bodies using a method that includes this polymerization process, the specific method is not particularly limited. For example, a method that polymerizes the zirconia composition within a mold can be used; a photolithography method (stereolithography; SLA) using the zirconia composition can also be employed. Among these, (b) photolithography (SLA) is preferred.

[0127] According to the photoforming method, a shape corresponding to the desired shape of the final sintered zirconia body can be imparted at a specific point in time during the manufacturing process of the zirconia molded body. Therefore, this photoforming method is sometimes particularly suitable for applications such as the use of sintered zirconia bodies as dental materials, such as dental repairs.

[0128] There is no particular limitation on the type of polymerizable monomer. It can be any of the following: monofunctional (meth)acrylates, monofunctional (meth)acrylamides, etc.; and multifunctional polymerizable monomers such as difunctional aromatic compounds, difunctional aliphatic compounds, and trifunctional or higher compounds. One type of polymerizable monomer can be used alone, or two or more types can be used. Among these, multifunctional polymerizable monomers are preferred, especially when using photoforming methods.

[0129] There are no particular limitations on oligomers as long as they are compounds that are bonded to two or more of the aforementioned polymerizable monomers and have polymerizable properties.

[0130] 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-methacryloyloxypropyltrimethoxysilane, and 11-methacryloyloxyundecyltrimethoxysilane.

[0131] 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.

[0132] 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.

[0133] Examples of difunctional aromatic compounds 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, and 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane. Propane, 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)benzothionate, etc. (meth)acrylates. 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.

[0134] 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, 1,4-butanediol di(meth)acrylate, 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, and 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate (commonly known as "UDMA"), etc. Among these, from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles, triethylene glycol dimethacrylate (commonly known as "TEGDMA") and UDMA are preferred.

[0135] 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 (meth)acrylates. 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.

[0136] In any of the methods described 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 a photopolymerization initiator is particularly preferred. As a photopolymerization initiator, it can be appropriately selected 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 for the purpose of gel casting.

[0137] When manufacturing zirconia molded bodies using a photoforming method with a pulverized zirconia composition, the specific method of photoforming is not particularly limited, and known methods can be appropriately used. For example, methods such as using a photoforming device to photopolymerize a liquid composition using ultraviolet light, laser, etc., thereby sequentially forming layers with the desired shape, thus obtaining the desired zirconia molded body, can be employed.

[0138] To further increase the density of the zirconia molded body as a cured product, CIP treatment can be carried out after humidifying the zirconia molded body.

[0139] In the case of pressure molding, the powder containing zirconia particles can be humidified before pressure molding. The humidification method can be any known method without limitation; it can involve spraying water using a sprayer, or using a humidifier or a constant temperature and humidity device. The increase in moisture due to humidification depends on the average particle size of the contained zirconia particles, the average particle size of the stabilizer particles, etc., and 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, relative to the mass of the powder before humidification and the molded body. It should be noted that the increase in moisture due to humidification can be calculated as a percentage by dividing the mass of the powder before humidification by the mass of the powder before humidification and the molded body (the mass of the powder after humidification and the molded body).

[0140] The pressure applied during CIP processing is the same as described above for the instructions on pressure molding.

[0141] (f) The process of stacking and shaping particles containing zirconium oxide particles and small particles. There are no particular limitations on the specific methods used to manufacture granules containing zirconium oxide particles and small particles. For example, a method can be used to produce granules by drying them in a spray dryer after slurry preparation, and the resulting granules can be used for powder lamination shaping.

[0142] There are no particular limitations on the powder lamination method, and examples include powder layering, SLS (Selective Laser Sintering), SLM (Selective Laser Melting), electron beam lamination, arc discharge lamination, and binder spraying. Regarding a better method that does not contain organic matter during lamination, it is preferable that organic matter is also not used in the particle manufacturing stage.

[0143] [Manufacturing method of zirconia pre-sintered body] Next, regarding the manufacturing method of zirconia pre-sintered body, we will take the case where the stabilizer is yttrium oxide as an example for explanation.

[0144] The zirconia pre-fired body of the present invention can be manufactured by pulverizing a zirconia composition and then calcining (pre-firing) the pulverized zirconia composition into a molded body until the zirconia particles do not sinter together. In the aforementioned pulverization process, by pulverizing under specified conditions, an excessive amount of energy is applied compared to the prior art.

[0145] From the viewpoint that the use of the specific zirconium oxide composition described above ensures a reliable semi-sintered state, the pre-firing temperature (maximum pre-firing temperature) in the pre-firing process 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.

[0146] Furthermore, from the viewpoint of ensuring processability, the preheating temperature is preferably below 1200°C, more preferably below 1150°C, even more preferably below 1100°C, and particularly preferably below 1050°C.

[0147] That is, the preferred temperature for manufacturing the zirconia pre-fired body of the present invention is 600~1200°C.

[0148] In addition, by using the aforementioned pulverization process, the target pre-burnt body can be obtained even in regions with lower temperatures than before (e.g., around 600–900°C) by using small particles containing a stabilizer concentration within a specified range.

[0149] Regarding the holding time (retention time) at the aforementioned highest pre-sintering temperature, there is no particular limitation as long as a semi-sintered zirconia pre-sintered body can be obtained, but it is preferable to hold it at the highest pre-sintering temperature for 30 minutes to 6 hours.

[0150] In addition, the heating rate up to the maximum preheating temperature and the cooling rate from the maximum preheating temperature are preferably 300°C / min or less.

[0151] In a suitable embodiment, the heating rate for raising the zirconia molded body of the present invention to the highest pre-firing temperature during pre-firing is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, even more preferably 0.5°C / min or more, and preferably 50°C / min or less, more preferably 30°C / min or less, even more preferably 20°C / min or less.

[0152] By setting the heating rate above or below the aforementioned lower limit, productivity is increased. Furthermore, by setting the heating rate below or below the aforementioned upper limit, the volume difference between the interior and exterior of the zirconia molded body and / or the zirconia pre-sintered body can be suppressed. Additionally, in the case where the zirconia molded body contains organic matter, the rapid decomposition of that organic matter can be suppressed, thereby preventing cracking and / or damage.

[0153] [Zirconium oxide pre-fired body] Next, the zirconia pre-fired body will be described.

[0154] The zirconia pre-fired body is obtained by pre-firing the zirconia molded body as described above.

[0155] The types and contents of stabilizers in the zirconia pre-fired body are the same as those in the zirconia composition.

[0156] Furthermore, the zirconia pre-sintered body of the present invention has excellent mechanical strength, and the opalescence can be controlled to an appropriate range. Therefore, there is no particular limitation. In one embodiment, the zirconia pre-sintered body of the present invention is designed from the viewpoint that sometimes the monoclinic crystallinity of zirconia is within a specified range and the sintered body is monolithic, resulting in better mechanical strength and light transmittance. The presence rate f of yttrium oxide (hereinafter also simply referred to as "undissolved yttrium oxide") not dissolved in zirconia is calculated using the following formula (1-1). y (%) is preferably less than 4%.

[0157] f y (%)=I y / (I m +I t +I c +I y )×100 (1-1) (where f) y f represents the presence rate of yttrium oxide that is not dissolved in zirconium oxide. y (%), in XRD determination, I m I represents the area intensity of the peak near 2θ = 28.2° at the apex of the main peak in a monoclinic crystal system. t I represents the area intensity of the peak near 2θ = 30.3° at the apex of the main peak of the tetragonal crystal system. c I represents the area intensity of the peak near 2θ = 30.0° at the apex of the main peak in a cubic crystal system. y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak of yttrium oxide, which is not dissolved in zirconium oxide.

[0158] It should be noted that, since the main peaks of the tetragonal and cubic crystal systems are located close to each other, the area intensity of their respective main peaks can be calculated through peak separation.

[0159] From the perspective that the zirconia sintered body obtained by acting integrally within the specified range through the aforementioned half-width is superior in mechanical strength and light transmittance, the presence rate f of undissolved yttrium oxide... y (%) is more preferably less than 3.5%, further preferably less than 2%, and particularly preferably less than 1%.

[0160] Furthermore, the presence rate f of unsolidified yttrium oxide y (%) can be 0%.

[0161] The presence rate f of unsolvable yttrium oxide y (%) can be adjusted by methods such as pulverization, as described below.

[0162] Furthermore, the zirconia pre-sintered body of the present invention exhibits excellent mechanical strength, and the opalescence can be controlled to an appropriate range. Therefore, there are no particular limitations. In one embodiment, the zirconia pre-sintered body of the present invention is designed from the viewpoint that it is integrated with small particles whose concentration of stabilizer is sometimes adjusted to a desired range, resulting in a sintered body with superior mechanical strength and light transmittance. The monoclinic crystal ratio f is calculated using formula (1-2). m (%) is preferably less than 55%.

[0163] f m (%)=I m / (I m +I t +I c +I y )×100 (1-2) (where f) m Indicates the monoclinic crystallinity (%); in XRD measurements, I m This represents the area intensity of the peak near 2θ = 28.2° at the apex of the main peak in a monoclinic crystal system; I t This represents the area intensity of the peak near 2θ = 30.3° at the apex of the main peak of the tetragonal crystal system; I c I represents the area intensity of the peak near 2θ = 30.0° at the apex of the main peak in a cubic crystal system; y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak where unsolidified yttrium oxide appears.

[0164] It should be noted that, since the main peaks of the tetragonal and cubic crystal systems are located close to each other, the area intensity of their respective main peaks can be calculated through peak separation.

[0165] From the perspective that zirconia sintered bodies obtained by acting integrally within the aforementioned half-value width within a specified range have superior mechanical strength and light transmittance, the monoclinic crystallinity f m(%) is more preferably less than 50%, further preferably less than 48%, and particularly preferably less than 45%.

[0166] In addition, the monoclinic crystal ratio f m (%) is preferably 5% or more, more preferably 10% or more, even more preferably 15% or more, and particularly preferably 20% or more.

[0167] The zirconia pre-fired body of the present invention can contain additives other than zirconia and stabilizers, as long as the effects of the present invention are achieved. Examples of such additives include colorants (including pigments, composite pigments and fluorescent agents), alumina (Al2O3), titanium dioxide (TiO2), and silicon dioxide (SiO2).

[0168] As the aforementioned pigment, examples include oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically NiO, Cr2O3, etc.) (excluding Y2O3 and CeO2), preferably oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb, and more preferably oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb.

[0169] In addition, the zirconia pre-calcined body of the present invention may be free of erbium oxide (Er2O3).

[0170] Examples of composite pigments mentioned above include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, and (Co,Zn)Al2O4. Examples of fluorescent agents include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl. 10 O 17 Eu et al.

[0171] The zirconia pre-sintered body of the present invention may contain a fluorescent agent. By containing a fluorescent agent in the zirconia pre-sintered body, the zirconia sintered body becomes fluorescent. The type of fluorescent agent is not particularly limited, and one or more substances capable of emitting fluorescence using light of any wavelength may be used.

[0172] Examples of fluorescent agents include substances containing metallic elements. Examples of such metallic elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one or more of these metallic elements. Among these metallic elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred.

[0173] Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the aforementioned metal elements. Other fluorescent agents include Y₂SiO₅:Ce, Y₂SiO₅:Tb, (Y,Gd,Eu)BO₃, Y₂O₃:Eu, YAG:Ce, ZnGa₂O₄:Zn, and BaMgAl. 10 O 17 Eu et al.

[0174] The content of fluorescent agent in the zirconia pre-sintered body is not particularly limited, and can be appropriately adjusted according to the type of fluorescent agent or the purpose of the zirconia sintered body. From the viewpoint that it can be preferably used as a dental patch, 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 pre-sintered body and calculated according to the oxide of the metal element contained in the fluorescent agent.

[0175] Furthermore, the content of the fluorescent agent is calculated based on the oxide of the metal element contained in the fluorescent agent. There are no limitations as long as it exhibits suitable fluorescence, and it can be set to less than 1% by mass, less than 0.5% by mass, or less than 0.1% by mass. By keeping this content above the lower limit mentioned above, the fluorescence is comparable to that of natural human teeth. In addition, by keeping this content below the upper limit mentioned above, the reduction in mechanical strength and light transmittance can be suppressed.

[0176] Furthermore, to ensure sufficient mechanical strength for machining in the pre-sintered state, the flexural strength of the zirconia pre-sintered body of the present invention is preferably 15 MPa or more. Additionally, to facilitate machining in the pre-sintered state, the flexural strength of the zirconia pre-sintered body is preferably 70 MPa or less, more preferably 60 MPa or less.

[0177] The aforementioned bending strength was determined according to ISO 6872:2015 (Dentistry - Ceramic materials), with only the dimensions of the test piece changed; a test piece measuring 5mm × 10mm × 50mm was used. The front and C-side of the test piece (the side formed by chamfering the corners of the test piece at a 45° angle) were finished along the length using 600-grit sandpaper. The test piece was positioned with its widest face facing the vertical direction (load direction). In the three-point bending test, the distance between the support points (span) was set to 30mm, and the crosshead speed was set to 0.5mm / minute.

[0178] Furthermore, the density of the zirconia pre-fired body of the present invention is preferably 2.7 g / cm³. 3 The above, more preferably 3.0 g / cm 3 The above is further preferred to be 3.2 g / cm³. 3 above.

[0179] In addition, the density of the zirconia pre-sintered body is preferably 4.0 g / cm³. 3 The preferred value is 3.8 g / cm³. 3 The following is a further preferred value: 3.6 g / cm³ 3 The following applies. When the density is within the aforementioned range, molding can be easily performed.

[0180] The density of the zirconia pre-sintered body can be calculated using the formula (mass of the zirconia pre-sintered body) / (volume of the zirconia pre-sintered body). For example, to determine the density of the zirconia pre-sintered body, one can change the cutting position of the zirconia pre-sintered body while cutting out 10mm square test pieces (n=3) at arbitrary locations. The mass and volume of the obtained test pieces are measured, and the arithmetic mean of the measured values ​​is calculated. Using this arithmetic mean, the density is calculated according to the formula above.

[0181] [Zirconium oxide sintered body] Next, the sintered zirconia body will be described.

[0182] Zirconia sintered body is obtained by calcining the zirconia pre-sintered body obtained by the operation as described above.

[0183] The content of stabilizer (suitably yttrium oxide) in the zirconia sintered body of the present invention is the same as the content of stabilizer in the zirconia pre-sintered body.

[0184] Since the zirconia sintered body of the present invention uses small particles as raw materials with the concentration of stabilizer adjusted to the desired range, the effect of controlling the opalescence to an appropriate range is excellent even in zirconia sintered bodies produced by calcination at the highest sintering temperature (e.g., 1550°C) with a residence time (holding time) of less than 10 minutes.

[0185] The zirconia sintered body of the present invention may contain a fluorescent agent. The fluorescent agent is the same as that in the zirconia pre-sintered body.

[0186] In this specification, regarding fluorescent agents, "100% by mass of zirconium oxide contained in the pre-sintered zirconium oxide body" can be understood as "100% by mass of zirconium oxide contained in the sintered zirconium oxide body".

[0187] The zirconia sintered body of the present invention may contain a colorant. Examples of colorants include those used in the zirconia pre-sintered body.

[0188] 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. From the viewpoint of preferably using it as a dental patch, 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, based on the conversion of oxides of metal elements contained in the colorant, relative to 100% by mass of zirconia contained in the zirconia sintered body. In addition, the content of colorant, based on the conversion of oxides of 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, can be 0.1% by mass or less, and further can be 0.05% by mass or less.

[0189] To adjust the light transmittance of the zirconia sintered body of the present invention, the zirconia sintered body of the present invention may contain a light transmittance modifier. Examples of light transmittance modifiers include substances identical to those used in the zirconia pre-sintered body.

[0190] The content of the light transmittance modifier in the zirconia sintered body is not particularly limited, and can be appropriately adjusted according to the type of light transmittance modifier and the intended use of the zirconia sintered body. From the viewpoint that it can be preferably used as a dental patch, the content is preferably 0.1% by mass or less relative to 100% by mass of zirconia contained in the zirconia sintered body.

[0191] [Method for manufacturing zirconia sintered bodies] As a method for manufacturing the zirconia sintered body of the present invention, a method for manufacturing the zirconia sintered body by calcining the aforementioned zirconia pre-sintered body can be listed.

[0192] The preferred manufacturing method includes a step of calcining the aforementioned zirconia pre-sintered body under normal pressure at a maximum sintering temperature exceeding 1200°C and below 1650°C (hereinafter also referred to as the "calcination step").

[0193] In a suitable embodiment, the zirconia pre-sintered body of the present invention, by using small particles containing a stabilizer concentration adjusted to a desired range, can, for example, easily produce a zirconia sintered body of the present invention with excellent light transmittance after a short sintering time of less than 10 minutes at the highest sintering temperature.

[0194] When the zirconia pre-sintered body of the present invention is calcined to produce a sintered body, the highest sintering temperature is preferably the condition that the light transmittance of the zirconia sintered body reaches its maximum.

[0195] Based on the above viewpoints, and considering the ease with which the desired zirconia sintered body can be obtained under normal pressure, the maximum sintering temperature is preferably above 1200°C, more preferably above 1250°C, and even more preferably above 1300°C. Furthermore, the maximum sintering temperature is preferably below 1650°C, more preferably below 1600°C, even more preferably below 1550°C, particularly preferably below 1500°C, and most preferably below 1450°C.

[0196] As one embodiment, a method for manufacturing a zirconia sintered body may be provided, which includes a calcination process with a maximum sintering temperature exceeding 1200°C and below 1450°C.

[0197] By setting the maximum sintering temperature above the lower limit and below the upper limit, sintering can be performed sufficiently, and a dense sintered body can be easily obtained. Furthermore, by setting the maximum sintering temperature below the upper limit, the deactivation of the fluorescent agent can be suppressed.

[0198] The holding time at the highest sintering temperature is preferably 15 minutes or more, more preferably 30 minutes or more, and even more preferably 40 minutes or more. Furthermore, it is preferably 20 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less.

[0199] When a sintered body is manufactured by sintering for a short time, if the holding time at the highest sintering temperature is 10 minutes or less, the sintering time is not particularly limited. Since the desired zirconia sintered body can be obtained efficiently and stably with good productivity, the holding time at the highest sintering temperature is preferably 10 minutes or less, more preferably 5 minutes or less, further preferably 3 minutes or less, and particularly preferably 2 minutes or less.

[0200] The holding time can be more than 30 seconds, more than 45 seconds, or more than 1 minute.

[0201] The light transmittance of the zirconia sintered body is not reduced during manufacturing, and the calcination time for manufacturing the sintered body can be shortened. In particular, the holding time at the highest sintering temperature for manufacturing the sintered body can be shortened to less than 10 minutes. This improves production efficiency, and when the zirconia pre-sintered body of the present invention is applied to dental articles, the size of the dental article used for treatment can be determined, the time from machining to the point where the dental article can be used for treatment can be shortened, and the time burden on patients can be reduced. Furthermore, energy costs can be reduced.

[0202] The heating and cooling rates in the calcination process are preferably set in a way that minimizes the time required for the calcination process. For example, the heating rate can be set according to the performance of the calcination furnace to reach the highest sintering temperature in the shortest possible time. The heating rate up to the highest sintering temperature can be set to, for example, 10°C / min or higher, 50°C / min or higher, 100°C / min or higher, 120°C / min or higher, 150°C / min or higher, 200°C / min or higher, 250°C / min or higher, 300°C / min or higher, or 350°C / min or higher. The cooling rate is preferably set at a rate that prevents defects such as cracks from forming in the sintered body. For example, the sintered body can be allowed to cool naturally at room temperature after heating.

[0203] The pre-calcination and calcination in this invention can be carried out using a calcination furnace. There is no particular limitation on the type of calcination furnace; for example, electric furnaces and degreasing furnaces commonly used in industry can be used.

[0204] Commercially available dental calcining furnaces (such as the trade name "Sintra CS" (manufactured by Shenpaz)) can be used.

[0205] The zirconia sintered body of the present invention can be manufactured even without HIP treatment. As an optional step, HIP treatment can be performed after sintering at atmospheric pressure to further improve light transmittance and mechanical strength.

[0206] Hereinafter, the sintered body obtained by sintering at the aforementioned highest 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".

[0207] HIP processing can be performed using a known hot isostatic pressing (HIP) apparatus.

[0208] When performing HIP treatment on a single-sintered body, the HIP pressure is not particularly limited. However, to obtain a dense sintered body with high mechanical strength, the HIP pressure is preferably 100 MPa or higher, more preferably 125 MPa or higher, and even more preferably 130 MPa or higher. Furthermore, the upper limit of the HIP pressure is not particularly limited; for example, it can be set to 400 MPa or lower, 300 MPa or lower, or even 200 MPa or lower.

[0209] When performing HIP treatment on the aforementioned primary sintered body, the heating 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. Furthermore, the heating 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 heating rate to the above lower limit or above, productivity will be improved.

[0210] When performing HIP treatment on the aforementioned sintered body, the HIP time is not particularly limited. However, to obtain a dense zirconia sintered body with high mechanical strength, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Furthermore, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0211] In the method for manufacturing zirconia sintered bodies of the present invention, when performing HIP treatment on the aforementioned primary sintered body, the pressure medium is not particularly limited. From the viewpoint of minimizing the impact on zirconia, the pressure medium can be selected from at least one of oxygen, oxygen containing 3% hydrogen, air, and inactive gases (such as nitrogen, argon, etc.).

[0212] When performing HIP treatment on the aforementioned primary sintered body under an oxygen-mixed gas atmosphere, the oxygen concentration is not particularly limited; for example, it can be set to be more than 0% and less than 20%.

[0213] When using an oxygen-mixed gas, at least one of the following inert gases (such as nitrogen, argon, etc.) can be selected as the gas other than oxygen.

[0214] During the aforementioned HIP treatment, if an inert gas or the like is used in a reducing atmosphere, blackening may sometimes occur due to oxygen deficiency. In this case, to remove the blackening, it is preferable to include a heat treatment process (hereinafter also referred to as "tempering") at 1650°C or below in the atmosphere or in an oxygen-excess atmosphere after the aforementioned HIP treatment. From the viewpoint of effectively performing the heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere.

[0215] An atmosphere with excess oxygen refers to an atmosphere where the oxygen concentration is higher than that in the atmosphere.

[0216] As an oxygen-excess atmosphere, there is no particular limitation as long as the oxygen concentration exceeds 21% and is less than 100%, and it can be appropriately selected from this range. For example, the oxygen concentration can be set to 100%. During the aforementioned HIP treatment, if an inert gas or the like is used in a reducing atmosphere, blackening may sometimes occur due to oxygen deficiency. In this case, to remove the blackening, it is preferable to include a heat treatment process (hereinafter also referred to as "tempering") at 1650°C or below in the atmosphere or an oxygen-excess atmosphere after the aforementioned HIP treatment step. From the viewpoint of effectively performing the heat treatment, it is more preferable to perform it in an oxygen-excess atmosphere. An oxygen-excess atmosphere refers to an oxygen concentration higher than that in the atmosphere. As an oxygen-excess atmosphere, there is no particular limitation as long as the oxygen concentration exceeds 21% and is less than 100%, and it can be appropriately selected from this range. For example, the oxygen concentration can be set to 100%.

[0217] The zirconia sintered body of the present invention is not particularly limited as long as it achieves the effects of the present invention. It can be a single sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment.

[0218] Depending on the aesthetic appeal of the zirconia sintered body (e.g., the color of dental repairs), the heat treatment temperature in the atmosphere or in an oxygen-rich atmosphere can be appropriately changed.

[0219] In a suitable embodiment, from the viewpoint of the aesthetics of the zirconia sintered body, the heat treatment temperature in the atmosphere or in an oxygen-excess atmosphere is preferably below 1650°C, more preferably below 1600°C, and even more preferably below 1550°C.

[0220] In another suitable embodiment, from the viewpoint of the aesthetics of the zirconia sintered body, the heat treatment temperature in the atmosphere or in an oxygen-excess atmosphere is preferably below 1400°C, more preferably below 1300°C, and even more preferably below 1200°C.

[0221] Furthermore, in any embodiment, the heat treatment temperature is preferably 500°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher.

[0222] The aforementioned tempering process can be performed using a standard dental zirconia calcination furnace. Commercially available zirconia calcination furnaces can be used. Examples of commercially available furnaces include Noritake KATANA (registered trademark) F-1, F-1N, F-2, and F-2N (all from SK Medical Electronics Co., Ltd.).

[0223] The zirconia sintered body obtained by calcining the zirconia pre-burnt body of the present invention is suitable for use in dental products.

[0224] Examples of dental products include, for example, inner crowns, frameworks, dental crowns, dental bridges, bridge abutments, implants, implant screws, implant fixation devices, implant bridges, implant bars, dental crowns, dentures, inlays, onlays, orthodontic wires, and veneers.

[0225] By using the zirconia pre-fired body of the present invention in components such as implant screws and implant fixation devices, gingival discoloration caused by metal can be suppressed when using metal materials, resulting in excellent aesthetics.

[0226] Furthermore, as for their manufacturing methods, appropriate methods can be selected according to various applications. For example, dental articles can be obtained by machining the zirconia pre-fired body of the present invention followed by calcination. It should be noted that a CAD / CAM system is preferably used in this machining process.

[0227] There are no particular limitations on the CAD / CAM system, and any known device may be used. Examples of known devices include, for instance, CAD / CAM systems such as "KATANA (registered trademark) CAD / CAM system" and those manufactured by Kuraray Noritake Dental Co., Ltd.

[0228] As long as the present invention achieves the effects of the present invention, it includes the implementation methods obtained by combining all or part of the above-described structures in various ways within the scope of the technical concept of the present invention. Example

[0229] Next, embodiments are listed to illustrate the present invention in more detail, but the present invention is not limited to these embodiments at all, and those skilled in the art can make various modifications within the scope of the technical concept of the present invention.

[0230] [Example 1] Commercially available monoclinic zirconia powder (Y₂O₃: 0 mol%) and commercially available yttrium oxide powder were added to water to prepare a concentration of 20-30% by mass (yttrium oxide content (the ratio of the number of moles of yttrium oxide to the total number of moles of zirconia and yttrium oxide): 4.5 mol%). These powders, along with zirconia grinding media (diameter: 0.1 mm), were placed in the container of a bead mill. The grinding process was set to 1 hour, and the mixture was ground using the bead mill to obtain a slurry.

[0231] The resulting slurry was then dried in a dryer at 85°C. The dried powder obtained after removing the moisture was added to ethanol using a sample bottle to a concentration of approximately 0.1% by mass, and then subjected to ultrasonic dispersion for 2–30 minutes to obtain an ethanol solvent-diluted slurry containing the zirconium oxide composition.

[0232] <TEM observation of zirconium oxide compositions> One to two drops of the prepared ethanol-diluted slurry were added to a TEM microgrid (trade names "NP-M10-25" and "Microgrid Mo100P", equivalent to 250 mesh, manufactured by STEM Co., Ltd.) and allowed to dry. After confirming that the powder was mounted on the grid using an optical microscope, measurements were performed using a TEM (trade name "JEM-ARM200F ACCELARM Atomic Resolution Electron Microscope", manufactured by Nippon Electron Co., Ltd.) at an accelerating voltage of 200 kV and magnifications of 200,000x or 1,500,000x. It should be noted that the magnification can be adjusted appropriately according to the particle size of the object being observed.

[0233] <Method for identifying zirconium oxide particles> For zirconium oxide particles (zirconia concentration of 80% or more by mass), the following method is used for identification.

[0234] When performing measurements at high magnification (200,000x) in bright-field TEM observation, using scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS), observation points with a zirconium oxide concentration of 80% by mass or higher (observation range 5×5 nm) are included, and particles with almost constant brightness are considered as a single zirconium oxide particle. Alternatively, in dark-field TEM, by using an accelerating voltage that sharpens the diffraction pattern of monoclinic zirconium oxide, particles with increased brightness are considered as a single zirconium oxide particle.

[0235] <Method for determining the average primary particle size of zirconia particles> The equivalent diameter of the circle (equivalent diameter of the area circle) of each particle identified by the aforementioned method for identifying zirconia particles is taken as the primary diameter of each particle. The average value of the equivalent diameter of the circle of 10 particles randomly selected in a field of view at a magnification of 200,000 times is taken as the average primary diameter of the zirconia particles.

[0236] <Methods for identifying small particles> For small particles, use the following method to identify them.

[0237] When using the TEM used in the aforementioned <TEM observation of zirconia compositions>, and performing measurements at ultra-high magnification (1.5 million times) in bright field of view in TEM observation, for particles smaller than the average primary particle size of the aforementioned zirconia particles, when focusing on one of the particles, visually confirm by visually identifying the location where the lattice stripes of the particle are interrupted (or switched) as a grain boundary, and regard them as small particles.

[0238] <Methods for determining the primary particle size and average primary particle size of small particles> The equivalent diameter of the circle (equivalent diameter of the area circle) of each particle identified by the aforementioned small particle discrimination method is taken as the first particle diameter of each particle. The average value of the equivalent diameter of the circle of 10 particles randomly selected in a field of view at a magnification of 200,000 times is taken as the average first particle diameter of the small particles.

[0239] <Method for Determination of Yttrium Oxide Concentration in Small Particles> For each small particle identified by the aforementioned small particle discrimination method, the yttrium oxide concentration of each small particle was determined in STEM-EDS (observation range 5×5nm).

[0240] In Example 1, when arbitrarily selecting 10 small particles from a single field of view with a magnification of 200,000 times, the concentration of yttrium oxide in all 10 of the aforementioned 10 small particles is in the range of 10 to 50% by mass.

[0241] <Method for determining the area ratio of zirconia particles and small particles> The area ratio (%) of zirconia particles to small particles is calculated by using the area of ​​10 zirconia particles randomly selected from multiple particles identified by the aforementioned method for distinguishing zirconia particles and small particles, and the area of ​​10 small particles randomly selected from a field of view at a magnification of 200,000x.

[0242] An organic binder is added to the slurry diluted with ethanol solvent as described above and mixed. The mixed slurry is dried and granulated using a spray dryer to obtain a powder. The powder is then fed into a cylindrical mold and uniaxially pressed at 33 MPa, followed by CIP treatment at 190 MPa to obtain a plate-shaped or disc-shaped molded body.

[0243] The resulting molded body was placed in an electric furnace and heated from room temperature at a rate of 10°C / min. It was then held at 500°C for 2 hours to degrease the organic components. Subsequently, the temperature was increased at a rate of 10°C / min and held at 875°C for 2 hours. Finally, it was slowly cooled at a rate of -10°C / min to obtain a zirconia pre-fired body.

[0244] Furthermore, the pre-sintered zirconia body was calcined under atmospheric pressure, a heating rate of 10℃ / min, a maximum sintering temperature of 1375℃, and a holding time of 2 hours to obtain a sintered zirconia body containing 4.5 mol% yttrium oxide. The resulting sintered zirconia body was white.

[0245] [Comparative Example 1] Regarding the pulverization process, instead of a bead mill, a ball mill (diameter: 2 mm) was used, and the pulverization time was changed to 20 hours. Otherwise, the zirconia pre-sintered body and zirconia sintered body of Comparative Example 1 were manufactured using the same method as in Example 1.

[0246] <3-point bending strength> The three-point flexural strength of zirconia sintered bodies was determined according to ISO 6872:2015.

[0247] Samples measuring 4 mm × 1.2 mm × 15 mm were prepared from the plate-shaped zirconia sintered bodies of each embodiment and comparative example. The samples were 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.

[0248] <Opaqueness (OP value) of zirconia sintered bodies> a was measured using a spectrophotometer (manufactured by Konica Mining Co., Ltd., "CM-3610A") * 透射 a * 反射 b * 透射 b * 反射 The OP value of the zirconia sintered body is calculated using the following formula.

[0249] [Number 1] In this measurement, an F11 light source was used to measure the reflected light, and the result was obtained from this. A disc-shaped zirconia sintered body with a diameter of 15 mm and a thickness of 1.0 mm, obtained by mirror polishing on both sides, was used as the sample in the measurement. The average value was calculated with n=3.

[0250] As an OP value, a value of 4.5 or higher and 9.0 or lower is considered acceptable.

[0251] [Table 1] .

[0252] In the table, the yttrium oxide content of the sintered body was 4.5 mol in Example 1 and Comparative Example 1.

[0253] Furthermore, using the yttrium oxide concentration of the small particles in Table 1, the zirconium oxide concentration (mass%) in the small particles can be calculated from 100 (mass%) - yttrium oxide concentration (mass%).

[0254] The above results confirm that the zirconia sintered body obtained by the zirconia pre-sintered body of the present invention has excellent mechanical strength and excellent effect in controlling opalescence to an appropriate range.

[0255] In Comparative Example 1, since it was a zirconium oxide composition with small particles containing 10-50% by mass and no stabilizer, the opalescence could not be controlled to an appropriate range, and the target physical properties could not be obtained.

[0256] Industrial utilization The zirconium oxide composition of the present invention is useful for the manufacture of dental articles (especially dental articles used in dental hospital treatments).

Claims

1. A zirconium oxide composition comprising zirconium oxide particles having a concentration of 80% by mass or more, and Small particles containing 10-50% by mass of stabilizers capable of suppressing the phase transformation of zirconium oxide. The aforementioned small particles have a primary particle size smaller than the average primary particle size of the aforementioned zirconia particles.

2. The zirconia composition of claim 1, wherein, Under TEM observation, 10 small particles were randomly selected, and at least 6 of the aforementioned 10 small particles were small particles with a concentration of the aforementioned stabilizer of 10-50% by mass.

3. The zirconia composition of claim 1 or 2, wherein, The average primary particle size of the aforementioned zirconium oxide particles is 0.06~0.17 μm.

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

5. The zirconia composition of claim 1 or 2, wherein, The aforementioned stabilizer that can suppress the phase transformation of zirconium oxide is yttrium oxide.

6. The zirconia composition of claim 1 or 2, wherein, Under TEM observation, the area ratio of the aforementioned zirconium oxide particles to the aforementioned small particles was 55 / 45 to 99 / 1.

7. A method of making the zirconia composition of claim 1 or 2, comprising: The process of manufacturing a raw material composition comprising zirconium oxide particles and particles of a stabilizer capable of inhibiting the phase transformation of zirconium oxide, and The pulverization process of pulverizing the aforementioned zirconium oxide composition. The aforementioned crushing process uses crushing media with a diameter of less than 1 mm.

8. The method of manufacturing a zirconia composition according to claim 7, wherein, The processing time for the aforementioned crushing process is 20 minutes to 2 hours.

9. The method of producing a zirconia composition according to claim 7, wherein, The average primary particle size of the aforementioned zirconium oxide particles is 0.06~0.17 μm.

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

11. The method of manufacturing a zirconia composition according to claim 7, wherein, The aforementioned stabilizer that can suppress the phase transformation of zirconium oxide is yttrium oxide.

12. The method for manufacturing the zirconium oxide composition according to claim 7, further comprising the steps of manufacturing a slurry comprising the aforementioned raw material composition and spray drying to granulate.

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