Zirconia pre-sintered body, composition, and methods for producing same

Abstract

The present invention provides a pre-sintered body and a composition which are for obtaining a zirconia sintered body that, after short sintering in which the time of holding at a maximum sintering temperature is 10 minutes or less, maintains high light transmissivity equivalent to that of when long sintering is performed. The present invention also provides methods for producing the same. The present invention relates to a zirconia pre-sintered body in which zirconia particles have been consolidated to a degree such that sintering is not achieved, said zirconia pre-sintered body comprising a stabilizer capable of suppressing phase transition of the zirconia, wherein the following expression (1) is satisfied when comparing ΔL1*(W-B) relating to a first sintered body produced by sintering at 1550°C for 120 minutes and ΔL2*(W-B) relating to a second sintered body produced by sintering at 1550°C for 10 minutes.　(1): ΔL2*(W-B) / ΔL1*(W-B)≥0.85

Description

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

[0001] The present invention relates to a zirconia calcined body and composition, and a method for producing the same. More specifically, the present invention relates to a zirconia (zirconium (IV) oxide; ZrO2) calcined body and composition that have high translucency even after short-time sintering, and a method for producing the same.

[0002] Oxide ceramics are widely used industrially, and in particular, zirconia sintered bodies containing yttria have recently been used as dental materials, such as dental prostheses, due to their high strength and aesthetic properties. As raw materials for such zirconia sintered bodies, zirconium oxide powder and yttrium oxide powder are often used individually or as a solid solution. These raw materials are pulverized, mixed, dried, molded, and heat-treated to obtain a calcined body (mill blank), which is then machined into a shape similar to the desired dental prosthesis and further sintered to produce dental materials such as dental prostheses.

[0003] When sintering dental prostheses, it is important that the shorter the treatment time, the shorter the time required for completion, and that the aesthetics of the prosthesis remain consistent regardless of the sintering time, i.e., that the translucency remains consistent regardless of the sintering time.

[0004] As a method for producing a zirconia sintered body, for example, a method has been proposed in Patent Document 1. Patent Document 1 discloses a method for producing a zirconia sintered body in which a tetragonal crystal in which zirconia and yttria are solid-solved is mixed with a cubic crystal in which zirconia and yttria are solid-solved.

[0005] On the other hand, sintering of zirconia proceeds while energy stabilization occurs, accompanied by changes in shape and crystalline phase due to mass transfer. Therefore, in the method of Patent Document 1, for example, if sintering is stopped after a short time, there are problems such as insufficient densification resulting in low transparency, or insufficient crystalline phase transition and / or crystallization resulting in low strength and / or transparency.

[0006] In order to solve the problem of sintering in such a short time, proposals have been made in Patent Documents 2 and 3. Patent Document 2 discloses that by using zirconium oxide and yttrium oxide individually as raw materials and simultaneously using a tetragonal solid solution of zirconium oxide and yttrium oxide, the difference in translucency between a zirconia sintered body obtained by short-term retention at the maximum sintering temperature of 30 minutes and a zirconia sintered body obtained by long-term retention with the retention time of about 2 hours is small, and further discloses that excellent translucency can be achieved with sintering for 15 minutes.

[0007] Furthermore, Patent Document 3 discloses a zirconia workpiece for dental cutting, which uses Zpex Smile (registered trademark) or the like as a powder material or workpiece used in producing a sintered body and has a porosity of 15 to 30%, and discloses that in a specific embodiment, a sintered body excellent in translucency and strength was obtained by sintering for a short period of time.

[0008] JP 2018-52806 A International Publication No. 2018 / 056330 JP 2020-033338 A

[0009] On the other hand, the shorter the sintering time, the more advantageous it is in terms of manufacturing costs. As a result of investigations by the present inventors, in order to further shorten the sintering time, the holding time at the maximum sintering temperature is further shortened from about 30 minutes to, for example, 10 minutes. In the invention of Patent Document 1, it has been confirmed that in a short-term holding time of, for example, 10 minutes, there is a problem in that the translucency is lower than in a long-term holding time of, for example, about 2 hours, because there is not a sufficient gradient in the concentrations of zirconium and yttrium to be able to utilize mass transfer between the tetragonal and cubic crystals to promote sintering.

[0010] Furthermore, in Patent Document 2, when the holding time at the maximum sintering temperature is shortened to 10 minutes, the proportion of monoclinic crystals remaining in the calcined body without undergoing phase transition is high, and the reaction rate for the phase transition from monoclinic crystals to tetragonal crystals or cubic crystals is insufficient. As a result, there is a problem in that the translucency is low when comparing a short-term holding time at the maximum sintering temperature of, for example, about 10 minutes with a long-term holding time of about 2 hours.

[0011] Furthermore, Patent Document 3 does not disclose the use of undissolved yttria in short-time sintering with a holding time of 2 minutes at the maximum sintering temperature, but only discloses a zirconia workpiece using yttrium dissolved in zirconia, and discloses that sufficient translucency cannot be obtained unless yttrium dissolved in zirconia is used in Reference Example 1. Furthermore, even in the case of short-time sintering, it does not clearly state that the translucency of a zirconia sintered body obtained by short-time sintering with a holding time of 2 minutes is comparable to that of a zirconia sintered body obtained by sintering with a holding time of 2 hours.

[0012] In Patent Document 3, the reason why sintering in a short time using an yttrium compound that is not solid-dissolved in zirconia cannot be performed is because an yttrium compound that is not solid-dissolved in zirconia is not a material that favors substance diffusion. Therefore, when a zirconia calcined body contains an yttrium compound that is not solid-dissolved in zirconia, there is a problem in that a zirconia sintered body obtained by short-term retention at the maximum sintering temperature for a holding time of about 10 minutes is lower than a zirconia sintered body obtained by long-term retention at the maximum sintering temperature for a holding time of about 2 hours.

[0013] An object of the present invention is to provide a zirconia calcined body and composition for obtaining a zirconia sintered body that can maintain high translucency equivalent to that achieved by long-term sintering after sintering for a short period of time, i.e., a holding time of 10 minutes or less at the maximum sintering temperature, as well as methods for producing the same.

[0014] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that, in a zirconia calcined body (mill blank), controlling the range of the average primary particle size of particles constituting the raw material powder used to produce the calcined body and the height of the concentration gradient of the zirconium element and the yttrium element between each crystallite contained in the particles, i.e., the range of the standard deviation of the distribution of the yttrium element in the microscopic region, is useful for favorably promoting material diffusion and obtaining a zirconia sintered body that can maintain high translucency after sintering for a short period of time, at the same level as that after sintering for a long period of time. Based on this finding, the present inventors have conducted further research and have completed the present invention.

[0015] That is, the present invention encompasses the following inventions: [1] A zirconia calcined body in which zirconia particles are consolidated to a degree that does not result in sintering, comprising zirconia and a stabilizer capable of suppressing a phase transition of zirconia, wherein, when ΔL1*(W-B) of a first sintered body produced by sintering the zirconia calcined body at 1550°C for 120 minutes is compared with ΔL2*(W-B) of a second sintered body produced by sintering the zirconia calcined body at 1550°C for 10 minutes, the zirconia calcined body satisfies the following formula (1): ΔL2*(W-B) / ΔL1*(W-B)≧0.85 (1) [2] The zirconia calcined body according to [1], which satisfies either the following condition (i) or (ii): (i) The zirconia contains tetragonal zirconia, and a part of the stabilizer is not solid-dissolved in the zirconia; or (ii) The zirconia contains monoclinic zirconia and cubic zirconia. [3] The zirconia calcined body according to [1] or [2], wherein the stabilizer is yttria (YO). [4] The zirconia calcined body according to [3], which satisfies any one of the following conditions (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6):(A-1) The zirconia contains monoclinic zirconia and tetragonal zirconia, the monoclinic content is 55% or more, the tetragonal content is 10% or more, and a portion of the yttria is not solid-dissolved in the zirconia; (A-2) The zirconia contains tetragonal zirconia, does not fall under (A-1), the tetragonal content is 10% or more, and a portion of the yttria is not solid-dissolved in the zirconia; (A-3) The zirconia contains monoclinic zirconia and cubic zirconia, the monoclinic content is 55% or more, and the cubic content is 15% or more; (A-4) The zirconia contains monoclinic zirconia and cubic zirconia, does not fall under (A-3), and the cubic content is 15% or more; (A-5) The zirconia contains tetragonal zirconia and cubic zirconia, the tetragonal content is 5% or more and less than 50%, the cubic content is 50% or more and less than 95%, and a portion of the yttria is not solid-dissolved in the zirconia; (A-6) The zirconia contains tetragonal zirconia and cubic zirconia, does not fall under (A-5), the cubic content is 10% or more and less than 50%, and a portion of the yttria is not solid-dissolved in the zirconia. The contents of tetragonal, cubic, and monoclinic crystals in (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6) are calculated from the following formulas: Tetragonal fraction f. t (%) = I t / (I m +I t +I c +I y )×100 (2-1) Cubic crystal ratio f c (%) = I c / (I m +I t +I c +I y ) × 100 (2-2) Monoclinic crystal ratio f m (%) = I m / (I m +It +I c +I y )×100 (2-3) (where f m is the monoclinic crystal ratio (%), f t is the tetragonal crystal ratio (%), f c represents the cubic crystal ratio (%), and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.2° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak at 2θ=30.1° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2°, where the peak top of the main peak of undissolved yttria appears.) [5] The zirconia calcined body according to [3] or [4], in which the standard deviation of the yttrium element distribution is 2 mol% or more and less than 21 mol%. [6] The zirconia calcined body according to [4] or [5], which satisfies the condition (A-1) or (A-2), and in which the proportion of yttria not dissolved in zirconia is 1 to 25%. [7] The zirconia calcined body according to [4] or [5], which satisfies the condition (A-3) or (A-4), and in which a portion of the yttria is not dissolved in zirconia, and in which the proportion of the yttria not dissolved in zirconia is 1 to 15%. [8] The zirconia calcined body according to any of [1] to [7], in which the content of the stabilizer is 2 to 9 mol% based on the total moles of zirconia and stabilizer. [9] Density is 3.6 g / cm 3

[10] The zirconia calcined body according to any one of [1] to [9], wherein the average primary particle size is 40 to 110 nm.

[11] A zirconia composition containing zirconia and a stabilizer capable of suppressing a phase transition of zirconia, wherein, when ΔL1*(W-B) of a first sintered body produced by sintering the zirconia composition at 1550°C for 120 minutes is compared with ΔL2*(W-B) of a second sintered body produced by sintering the zirconia composition at 1550°C for 10 minutes, the zirconia composition satisfies the following formula (1): ΔL2*(W-B) / ΔL1*(W-B)≧0.85 (1)

[12] The zirconia composition according to

[11] , wherein the zirconia composition satisfies either the following condition (i) or (ii): (i) The zirconia powder (T) is a tetragonal zirconia, and a stabilizer powder is one in which a portion of the stabilizer is not solid-dissolved in the zirconia; or (ii) The zirconia powder (M) is a monoclinic zirconia, and a cubic zirconia powder (C) is included.

[13] The zirconia composition according to

[12] , which satisfies the condition (i) and further contains a monoclinic zirconia powder (M).

[14] The zirconia composition according to

[13] , in which the ratio of the total mass of the zirconia powder (T) and the zirconia powder (M) to the mass of the stabilizer powder is 85.0 mass%:15.0 mass% to 99.8 mass%:0.2 mass%.

[15] The zirconia composition according to

[13] or

[14] , in which the zirconia powder (M) accounts for 0 to 85 mass% of the total mass of the zirconia powder (T) and the zirconia powder (M).

[16] The zirconia composition according to any one of

[12] to

[15] , wherein the zirconia powder (T) contains a stabilizer capable of suppressing the phase transition of dissolved zirconia, and the content of the dissolved stabilizer is 2 to 4 mol% relative to the total moles of zirconia and stabilizer.

[17] The zirconia composition according to

[12] , which satisfies the condition (ii) and further wherein a portion of the stabilizer is not dissolved in zirconia.

[18] The zirconia composition according to

[12] or

[17] , wherein the ratio of the total mass of the zirconia powder (M) and the zirconia powder (C) to the mass of the stabilizer powder is 85.0 mass%:15.0 mass% to 100 mass%:0 mass%.

[19] The zirconia composition according to

[12] ,

[17] or

[18] , wherein the zirconia powder (C) accounts for 15.0 to 95.0 mass% of the total mass of the zirconia powder (M) and the zirconia powder (C).

[20] The zirconia composition according to any one of

[12] ,

[17] to

[19] , wherein the content of the stabilizer in the zirconia powder (M) is 0 to 1 mol% based on the total moles of the zirconia powder (M) and the stabilizer.

[21] The zirconia composition according to any one of

[12] ,

[17] to

[20] , wherein the zirconia powder (C) contains a stabilizer capable of suppressing the phase transition of dissolved zirconia, and the content of the dissolved stabilizer is 5 mol% to 15 mol% based on the total moles of the zirconia powder (C) and the stabilizer.

[22] The zirconia composition according to

[12] , which satisfies the condition (i) and further contains a cubic zirconia powder (T), wherein the ratio of the total mass of the zirconia powder (T) and the zirconia powder (C) to the mass of the stabilizer powder is 88.0 mass%:12.0 mass% to 99.999 mass%:0.001 mass%.

[23] The zirconia composition according to any one of

[11] to

[22] , wherein the average primary particle size (r1) of the zirconia powder (T), the zirconia powder (C), and the zirconia powder (M) is 40 to 110 nm.

[24] A method for producing a calcined zirconia body, which comprises firing the zirconia composition according to

[11] to

[23] to a degree that does not result in sintering of the zirconia particles.

[25] A method for producing a sintered zirconia body, which comprises sintering the calcined zirconia body according to [1] to

[10] .

[0016] By using the zirconia calcined body and composition of the present invention and their manufacturing methods, it is possible to obtain a zirconia sintered body that can maintain high translucency equivalent to that obtained by long-term sintering after sintering for a short period of time, i.e., a holding time at the maximum sintering temperature of 10 minutes or less. Furthermore, by using the zirconia calcined body and composition of the present invention and their manufacturing methods, it is possible to obtain a zirconia sintered body that can maintain high translucency equivalent to that obtained by long-term sintering after sintering for a short period of time, i.e., a holding time at the maximum sintering temperature of less than 1600°C (particularly preferably, 1560°C or less) of 10 minutes or less. Therefore, the manufacturing efficiency is excellent, and the method is industrially advantageous.

[0017] The zirconia calcined body of the present invention contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, and when ΔL1*(W-B) of a first sintered body produced by sintering at 1550°C for 120 minutes is compared with ΔL2*(W-B) of a second sintered body produced by sintering at 1550°C for 10 minutes, the following formula (1) is satisfied: ΔL2*(W-B) / ΔL1*(W-B)≧0.85 (1)

[0018] A zirconia calcined body can be a precursor (intermediate product) of a zirconia sintered body. In this specification, a zirconia calcined body is a body in which zirconia particles are solidified to a degree that does not result in sintering. The term "to a degree that does not result in sintering" refers to a state in which the zirconia particles are not completely sintered (semi-sintered state). In a completely sintered body, the relative density increases with sintering and densification progresses, so the relative density of the zirconia sintered body is 95% or more. The relative density can be calculated as the ratio of the actual density measured by Archimedes' method to the theoretical density. In this specification, the upper and lower limits of the numerical ranges (contents of each component, values ​​calculated from each component, and each physical property, etc.) can be appropriately combined. In addition, in this specification, the tetragonality f calculated by the following formulas (2-1), (2-2), (2-3), and (2-4) is used. t , cubic crystal fraction f c , monoclinic fraction f m , the content of undissolved yttria f y The total amount does not exceed 100%.

[0019] [Zirconia Calcined Body] The zirconia calcined body of the present invention contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia (hereinafter, also simply referred to as "stabilizer").

[0020] Examples of the stabilizer include calcium oxide (CaO), magnesium oxide (MgO), and yttrium oxide (YO 3、 Hereinafter, also referred to as "yttria."), cerium oxide (CeO2), scandium oxide (Sc2O3), niobium oxide (Nb2O5), lanthanum oxide (La2O3), erbium oxide (Er2O3), praseodymium oxide (Pr2O3, Pr6O11 Examples of the stabilizer include oxides such as samarium oxide (SmO), europium oxide (EuO), thulium oxide (TmO), gallium oxide (GaO), indium oxide (InO), and ytterbium oxide (YbO), with yttria being preferred. One type of stabilizer may be blended alone, or two or more types may be blended in combination.

[0021] The stabilizer content in the zirconia calcined body of the present invention is preferably 2 mol% or more, more preferably 3 mol% or more, even more preferably 3.5 mol% or more, and particularly preferably 4 mol% or more, based on the total moles of zirconia (zirconium (IV) oxide; ZrO2) and stabilizer. A content of 2 mol% or more is preferable because the crystal structure contained in the zirconia sintered body contains more cubic crystals, improving translucency. Furthermore, the stabilizer content is preferably 9 mol% or less, more preferably 8 mol% or less, even more preferably 7.5 mol% or less, and particularly preferably 7 mol% or less, from the viewpoint of suppressing a decrease in strength of the sintered body. The stabilizer content may be within any combination of these ranges. For example, the stabilizer content is preferably 2 to 9 mol%, more preferably 3 to 8 mol%, even more preferably 3.5 to 7.5 mol%, and particularly preferably 4 to 7 mol%. The content of the stabilizer in the zirconia calcined body of the present invention can be adjusted by changing the compounding ratios in consideration of the content of the stabilizer dissolved in each crystal system, for example, by adjusting the content of the stabilizer that is not dissolved in the zirconia composition described below, or by adjusting the content of cubic zirconia that has a high content of the stabilizer dissolved in zirconia.

[0022] In this specification, the content of the stabilizer means the total content of the stabilizer dissolved in zirconia and the stabilizer not dissolved in zirconia.

[0023] The stabilizer content in the zirconia calcined body of the present invention can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis (XRF), or the like.

[0024] The zirconia calcined body of the present invention satisfies the following formula (1) when comparing ΔL1 * (W-B) of the first sintered body produced by sintering at 1550°C for 120 minutes with ΔL2 * (W-B) of the second sintered body produced by sintering at 1550°C for 10 minutes: ΔL2 * (W-B) / ΔL1 * (W-B) ≧ 0.85 (1)

[0025] ΔL1 * (W-B) for the first sintered body and ΔL2 * (W-B) for the second sintered body are both values ​​calculated using the L* value of lightness (color space) in the L*a*b* color system (JIS Z 8781-4:2013 Colorimetry - Part 4: CIE 1976 L*a*b* color space). The lightness L* value can be measured under a D65 light source using, for example, a spectrophotometer manufactured by Olympus Corporation (product name "Crystal Eye"), or a spectrophotometer CM-3610A or CM-36dGV manufactured by Konica Minolta, Inc.

[0026] ΔL1*(W-B) for the first sintered body and ΔL2*(W-B) for the second sintered body are both measured by measuring the lightness (LW*) of the sample (zirconia sintered body) against a white background, and the lightness (LB*) of the same sample for which LW* was measured, measured against a black background using the same measuring device, measuring mode, and light source.The difference between these values ​​(ΔL*=(LW*)-(LB*)) represents an index of translucency.In evaluating ΔL1*(W-B) for the first sintered body and ΔL2*(W-B) for the second sintered body, the maximum sintering temperature was 1550°C in both cases, and the heating and cooling rates were the same. In the evaluation of ΔL1*(W-B) for the first sintered body, the holding time (holding time) at the maximum sintering temperature was 120 minutes (hereinafter, sintering with a holding time at the maximum sintering temperature of 120 minutes will also be referred to as "120-minute sintering" or "long-term sintering"). In the evaluation of ΔL2*(W-B) for the second sintered body, the holding time (holding time) at the maximum sintering temperature was 10 minutes (hereinafter, sintering with a holding time at the maximum sintering temperature of 10 minutes will also be referred to as "10-minute sintering" or "short-time sintering").

[0027] The reason why the zirconia calcined body of the present invention can provide a zirconia sintered body that can maintain high translucency equivalent to that of a zirconia sintered body sintered for a long time, even after a short sintering time of 10 minutes or less at the maximum sintering temperature, is thought to be as follows. Hereinafter, an example in which the stabilizer is yttria will be described, but the present invention is not limited to the case in which the stabilizer is yttria. Normally, when the holding time at the maximum sintering temperature is shortened to 10 minutes, if the concentration gradient of the stabilizer metal element (preferably yttrium element) in the zirconia crystal system is small, there is almost no transfer of yttrium element or yttrium ions between substances. Therefore, there are difficulties with 10-minute sintering, such as insufficient stabilization of energy associated with substance transfer, insufficient sintering, and reduced translucency. In contrast to this, as shown in an embodiment according to any of the following conditions (i) or (ii) (for example, conditions (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6)), by selecting a zirconia powder and a yttria powder of a specific crystal system according to the amount of yttria dissolved, etc., and producing a calcined body, a source that supplies elemental yttrium or yttrium ions and a destination to which the elemental yttrium or yttrium ions move are present within the system of the zirconia calcined body, and an appropriate concentration gradient of elemental yttrium or yttrium ions is achieved between the two, and elemental yttrium or yttrium ions move between crystals in the zirconia crystal system during sintering.In this way, by having a zirconia crystal system or yttrium source as a supplier that supplies elemental yttrium or yttrium ions, and a zirconia crystal system as a destination to which elemental yttrium or yttrium ions can migrate, present within the system of the zirconia calcined body, the difference in concentration of elemental yttrium or yttrium ions between the substances present in the system during sintering is increased, and material transfer occurs as particles solidify during sintering. As a result, even during a short sintering time of 10 minutes or less, the migration of elemental yttrium or yttrium ions progresses sufficiently, and when combined with a raw material powder having a predetermined average particle size, they act together, resulting in a more uniform distribution of elemental yttrium in the resulting zirconia sintered body. It is therefore believed that the translucency of the zirconia sintered body satisfies the above formula (1).

[0028] Patent Document 3 discloses an example in which the holding time at the maximum sintering temperature was shortened to 2 minutes only when using zirconia powder containing 4 mol% to 5.5 mol% of yttrium dissolved in zirconia. However, in the example in Patent Document 3, the holding time was shortened not by dispersing a non-dissolved yttrium compound on the outermost surface of the zirconia particles as in the other examples, but by using only yttrium dissolved in zirconia, and by performing CIP treatment multiple times (specifically, 5 to 10 times) to reduce the porosity of the workpiece, and then sintering at a high temperature of 1600 °C. This manufacturing method, which requires both repeated CIP treatment five or more times to obtain a workpiece and then high-temperature treatment at a maximum sintering temperature of 1600 °C, has poor manufacturing efficiency and is industrially disadvantageous from a cost perspective, leaving room for improvement.

[0029] In contrast, as described above, the present invention increases the difference in the concentrations of yttrium element or yttrium ions between substances present in the sintering system during sintering, thereby promoting mass transfer during sintering. This allows for excellent translucency even in a short sintering time of 10 minutes or less, even at a maximum sintering temperature of less than 1600°C. Therefore, unlike Patent Document 3, repeated CIP treatment five or more times is not required during production of a molded body. The maximum sintering temperature is lower and the sintering time is shorter, achieving both a lower maximum sintering temperature and a shorter sintering time, which is industrially advantageous. The present invention can achieve the effects of the present invention even in crystal systems different from those of Patent Document 3 (e.g., a crystal system in which the monoclinic content of the zirconia constituting the zirconia calcined body is 55% or more), as long as the migration of yttrium element or yttrium ions can be promoted.

[0030] As described above, the present invention can achieve the effects of the present invention even when using yttria that is not dissolved in zirconia (hereinafter also referred to as "undissolved yttria"). This is an advantage that differs from Patent Document 3, which shows in Reference Example 1 that unless 4 mol% or more of dissolved yttrium is used, the amount of dissolved yttrium is insufficient to sufficiently promote phase transition with short-time sintering, and sufficient translucency cannot be obtained.

[0031] Hereinafter, a preferred embodiment will be described taking the case where the stabilizer is yttria as an example. The present invention is not limited to the case where the stabilizer is yttria. Therefore, when another stabilizer is used, the "yttria content" can be read as the content of the other stabilizer, and the "yttrium element distribution" can be read as the element distribution of the other metal element.

[0032] In the zirconia calcined body of the present invention, the standard deviation of the yttrium element distribution is preferably 2 mol% or more, from the viewpoint that migration of yttrium element or yttrium ions is likely to occur during short-time sintering and the resulting zirconia sintered body has excellent translucency. From the viewpoint of even better translucency, the standard deviation of the yttrium element distribution is more preferably 2.1 mol% or more, even more preferably 2.5 mol% or more, and particularly preferably 3 mol% or more. Furthermore, from the viewpoint that migration of yttrium element or yttrium ions is likely to occur between substances present in the sintering system during short-time sintering and the resulting zirconia sintered body has excellent translucency, the standard deviation of the yttrium element distribution is preferably less than 21 mol%, more preferably 20 mol% or less, even more preferably 18 mol% or less, and particularly preferably 15 mol% or less. The standard deviation of the yttrium element distribution may be within any combination of these ranges. For example, the standard deviation of the yttrium element distribution is preferably 2 mol% or more and less than 21 mol%, more preferably 2.1 mol% or more and 20 mol% or less, even more preferably 2.5 mol% or more and 18 mol% or less, and particularly preferably 3 mol% or more and 15 mol% or less. In one preferred embodiment, a zirconia calcined body having a standard deviation of 2.1 mol% or more and 15 mol% or less can be mentioned. The standard deviation of the yttrium element distribution is determined by the content f of undissolved yttria. y The content of undissolved yttria can be adjusted by adjusting the average particle size of the raw material powder used as the yttrium source, the content of the raw material powder in the raw material composition, the blending ratio, etc. y This can be more easily adjusted by adjusting the predetermined average particle size of the raw material powder used as the yttrium source.

[0033] The method for calculating the standard deviation of the yttrium element distribution is as described in the Examples below.

[0034] In the zirconia calcined body of the present invention, migration of elemental yttrium or yttrium ions is likely to occur during short-term sintering, and the resulting zirconia sintered body has excellent translucency. Therefore, the zirconia calcined body of the present invention preferably satisfies either of the following conditions (i) or (ii): (i) the zirconia contains tetragonal zirconia, and a portion of the stabilizer is not solid-dissolved in the zirconia; or (ii) the zirconia contains monoclinic zirconia and cubic zirconia.

[0035] Examples of embodiments of condition (i) include a zirconia calcined body in which the zirconia contains only tetragonal zirconia and a portion of the stabilizer is not solid-dissolved in the zirconia; a zirconia calcined body in which the zirconia contains monoclinic zirconia and tetragonal zirconia and a portion of the stabilizer is not solid-dissolved in the zirconia; and a zirconia calcined body in which the zirconia contains tetragonal zirconia and cubic zirconia and a portion of the stabilizer is not solid-dissolved in the zirconia. Specifically, embodiments of condition (i) are preferably zirconia calcined bodies that satisfy any of the following conditions (A-1), (A-2), (A-5), or (A-6). Specifically, embodiments of condition (ii) are preferably zirconia calcined bodies that satisfy any of the following conditions (A-3) or (A-4). In any embodiment, the yttria content, the standard deviation of the yttrium element distribution, and the like can be selected in appropriate combination within the ranges described in this specification.(A-1) The zirconia contains monoclinic zirconia and tetragonal zirconia, the monoclinic content is 55% or more, the tetragonal content is 10% or more, and a portion of the yttria is not solid-dissolved in the zirconia; (A-2) The zirconia contains tetragonal zirconia, does not fall under (A-1), the tetragonal content is 10% or more, and a portion of the yttria is not solid-dissolved in the zirconia; (A-3) The zirconia contains monoclinic zirconia and cubic zirconia, the monoclinic content is 55% or more, and the cubic content is 15% or more; (A-4) The zirconia contains monoclinic zirconia and cubic zirconia, does not fall under (A-3), and the cubic content is 15% or more; (A-5) The zirconia contains tetragonal zirconia and cubic zirconia, the tetragonal content is 5% or more and less than 50%, the cubic content is 50% or more and less than 95%, and part of the yttria is not solid-dissolved in the zirconia; (A-6) The zirconia contains tetragonal zirconia and cubic zirconia, does not fall under (A-5), the cubic content is 10% or more and less than 50%, and part of the yttria is not solid-dissolved in the zirconia. The contents of tetragonal, cubic, and monoclinic crystals in (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6) are calculated from the following formulas: Tetragonal fraction f. t (%) = I t / (I m +I t +I c +I y )×100 (2-1) Cubic crystal ratio f c (%) = I c / (I m +I t +I c +I y ) × 100 (2-2) Monoclinic crystal ratio f m (%) = I m / (I m +It +I c +I y )×100 (2-3) (where f m is the monoclinic crystal ratio (%), f t is the tetragonal crystal ratio (%), f c represents the cubic crystal ratio (%), and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.2° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak at 2θ=30.1° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2° where the peak top of the main peak of undissolved yttria appears.)

[0036] Hereinafter, embodiments (A-1), (A-2), (A-3), (A-4), (A-5) and (A-6) will be described one by one as examples of preferred embodiments.

[0037] The contents of the tetragonal, cubic, and monoclinic crystals in the embodiments (A-1), (A-2), (A-3), (A-4), (A-5), and (A-6) are calculated from the above formulas (2-1), (2-2), and (2-3), respectively. The methods for measuring the contents of the tetragonal, cubic, and monoclinic crystals are as described in the Examples below.

[0038] <Embodiment (A-1)> A preferred embodiment (A-1) is a zirconia calcined body containing monoclinic zirconia and tetragonal zirconia, wherein the monoclinic content is 55% or more and the tetragonal content is 10% or more, and a portion of the yttria is not solid-dissolved in the zirconia (hereinafter, also referred to as "Embodiment (A-1)").

[0039] In embodiment (A-1), the monoclinic content is preferably 55% or more, more preferably 56% or more, even more preferably 58% or more, and particularly preferably 60% or more. The monoclinic content is preferably 85% or less, more preferably 80% or less, even more preferably 75% or less, and particularly preferably 70% or less. The monoclinic content may be any combination of these ranges. For example, the monoclinic content is preferably 55% or more and 85% or less, more preferably 56% or more and 80% or less, even more preferably 58% or more and 75% or less, and particularly preferably 60% or more and 70% or less. When the monoclinic content is within the above range, when combined with tetragonal zirconia of a predetermined content, the difference in the concentration of yttrium element or yttrium ion in the system during sintering can be set to a desired range. When combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal elements or their ions constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency. Note that, in this specification, the difference in concentration is not particularly limited, as long as the desired standard deviation range is obtained in the sintered zirconia sintered body and the translucency satisfies Equation (1). The method for measuring the monoclinic content is as described in the Examples below.

[0040] In embodiment (A-1), the tetragonal content is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and particularly preferably 25% or more. The tetragonal content is preferably 44% or less, more preferably 42% or less, even more preferably 40% or less, and particularly preferably 38% or less. The tetragonal content may be any combination of these ranges. For example, the tetragonal content is preferably 10% or more and 44% or less, more preferably 15% or more and 42% or less, even more preferably 20% or more and 40% or less, and particularly preferably 25% or more and 38% or less. When the tetragonal content is within the above range, when combined with monoclinic zirconia supplied as a destination for yttrium element or yttrium ions, the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set within a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, sufficiently promoting the migration of the metal element or its ion constituting the stabilizer even during a short sintering time of 10 minutes or less, resulting in a zirconia sintered body with excellent translucency. The method for measuring the tetragonal content is as described in the Examples below.

[0041] Another preferred embodiment is a zirconia calcined body in which the content of the monoclinic system is 55% or more and 75% or less, and the content of the tetragonal system is 25% or more and 45% or less.

[0042] In embodiment (A-1), another preferred embodiment is a zirconia calcined body in which the proportion of yttria not dissolved in the zirconia is 1 to 25%.

[0043] In the zirconia calcined body according to embodiment (A-1), the proportion of yttria that is not dissolved in zirconia (hereinafter referred to as the "content of undissolved yttria f y " or "f y ") can be calculated based on the following formula (2-4): y (%) = I y / (Im +I t +I c +I y )×100 (2-4) (where f y represents the proportion (%) of undissolved yttria, and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.2° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak at 2θ=30.1° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2° where the peak top of the main peak of undissolved yttria appears.)

[0044] In embodiment (A-1), when tetragonal zirconia and monoclinic zirconia are combined, the concentration gradient of the yttrium element can be set within a desired range, the yttrium element is likely to move even in a short sintering time, and the resulting zirconia sintered body has excellent translucency. Therefore, the content f of undissolved yttria is preferably 0.05 to 0.15. y is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 3.5% or more. y is preferably 25% or less in terms of being able to suppress a decrease in strength of the sintered body, and is more preferably 20% or less, even more preferably 18% or less, and particularly preferably 16% or less in terms of being able to reduce the standard deviation of the yttrium element distribution, making it easier for the yttrium element to migrate during short-term sintering, and providing the resulting zirconia sintered body with better translucency. y For example, the content f of undissolved yttria may be in the range of any combination thereof. y The content f of undissolved yttria is preferably 1 to 25%, more preferably 2 to 20%, further preferably 3 to 18%, and particularly preferably 3.5 to 16%.y can be adjusted by adjusting the predetermined average particle size of the yttria powder used as the yttrium source, the content and blending ratio of the predetermined yttria powder in the raw material composition, and the like.

[0045] In embodiment (A-1), the zirconia in the zirconia calcined body may contain a cubic crystal system, but preferably does not contain a cubic crystal system, since this facilitates the migration of yttrium element or yttrium ions. In other words, in embodiment (A-1), it is preferable that the zirconia calcined body does not simultaneously contain a cubic crystal system and a tetragonal crystal system.

[0046] <Embodiment (A-2)> A preferred embodiment (A-2) is a zirconia calcined body that contains tetragonal zirconia, does not fall under (A-1), has a tetragonal content of 10% or more, and is yttria that is not partly dissolved in zirconia (hereinafter, also referred to as "embodiment (A-2)").

[0047] In embodiment (A-2), the zirconia in the zirconia calcined body contains a tetragonal crystal. The tetragonal crystal content is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and particularly preferably 25% or more. Furthermore, in order to prevent a decrease in the strength of the sintered body, the tetragonal crystal content is preferably less than 98%, more preferably 97.5% or less, even more preferably 97% or less, and particularly preferably 96.5% or less. The tetragonal crystal content may be any combination of these ranges. For example, the tetragonal crystal content is preferably 10% or more and 98% or less, more preferably 15% or more and 97.5% or less, even more preferably 20% or more and 97% or less, and particularly preferably 25% or more and 96.5% or less. In another embodiment, the zirconia sintered body does not contain monoclinic zirconia. For example, the tetragonal content is preferably greater than 45% and less than 98%, more preferably 55% to 97.5%, even more preferably 70% to 97%, and particularly preferably 80% to 96.5%. When the tetragonal content is within the above range, when combined with undissolved yttria, the difference in the concentration of yttrium element or yttrium ions in the sintered body can be adjusted to a desired range. When combined with a raw material powder having a predetermined average particle size, the zirconia sintered body acts integrally with the stabilizer, sufficiently promoting the migration of metal elements or their ions constituting the stabilizer, even during short sintering times of 10 minutes or less, resulting in an excellent translucency. The tetragonal content is measured as described in the Examples below.

[0048] Since embodiment (A-2) does not fall under embodiment (A-1), the monoclinic content is 0% or more and less than 55%. The monoclinic content is preferably 1% or more, more preferably 2% or more, even more preferably 2.5% or more, and particularly preferably 10% or more. Furthermore, the monoclinic content is preferably less than 55%, more preferably 50% or less, even more preferably 40% or less, and particularly preferably 30% or less. The monoclinic content may be any combination of these ranges. For example, the monoclinic content is preferably 1% or more and less than 55%, more preferably 2% or more and less than 50%, even more preferably 2.5% or more and less than 40%, and particularly preferably 10% or more and less than 30%.

[0049] Another preferred embodiment is a zirconia calcined body in which the zirconia in the calcined body contains a tetragonal crystal, the content of the monoclinic crystal is 0%, and the content of the tetragonal crystal is 80% or more and 97% or less, and a part of the stabilizer is not solid-dissolved in the zirconia.

[0050] In the embodiment (A-2), a part of the stabilizer, which is yttria contained in the calcined zirconia body, is undissolved yttria.

[0051] In the zirconia calcined body according to embodiment (A-2), the content f of undissolved yttria y can be calculated based on the above formula (2-4).

[0052] In the embodiment (A-2), the content of undissolved yttria f y When combined with tetragonal zirconia, the concentration gradient of the yttrium element can be set within a desired range, the yttrium element is likely to migrate even during short-time sintering, and the resulting zirconia sintered body has excellent translucency. Therefore, the content f of undissolved yttria is preferably more than 2%, more preferably 2.5% or more, even more preferably 3% or more, and particularly preferably 3.5% or more. yis preferably 25% or less in terms of being able to suppress a decrease in strength of the sintered body, and is more preferably 20% or less, even more preferably 18% or less, and particularly preferably 16% or less in terms of being able to reduce the standard deviation of the yttrium element distribution, making it easier for the yttrium element to migrate during short-term sintering, and providing the resulting zirconia sintered body with better translucency. y For example, the content f of undissolved yttria may be in the range of any combination thereof. y is preferably 1 to 25%, more preferably 2 to 20%, further preferably 3 to 18%, and particularly preferably 3.5 to 16%.

[0053] In embodiment (A-2), the zirconia in the zirconia calcined body may contain a cubic crystal system, but preferably does not contain a cubic crystal system, since this facilitates the migration of yttrium element or yttrium ions. In other words, in embodiment (A-2), it is preferable that the zirconia calcined body does not simultaneously contain a cubic crystal system and a tetragonal crystal system.

[0054] <Embodiment (A-3)> A preferred embodiment (A-3) includes a zirconia calcined body containing monoclinic zirconia and cubic zirconia, wherein the monoclinic zirconia content is 55% or more and the cubic zirconia content is 15% or more (hereinafter, also referred to as "Embodiment (A-3)").

[0055] In embodiment (A-3), the monoclinic content is preferably 55% or more, more preferably 56% or more, even more preferably 58% or more, and particularly preferably 60% or more. The monoclinic content is preferably 85% or less, more preferably 80% or less, even more preferably 75% or less, and particularly preferably 70% or less. The monoclinic content may be any combination of these ranges. For example, the monoclinic content is preferably 55% or more and 85% or less, more preferably 56% or more and 80% or less, even more preferably 58% or more and 75% or less, and particularly preferably 60% or more and 70% or less. When the monoclinic content is within the above range, when cubic zirconia with a predetermined content is combined with undissolved yttria as needed, the difference in concentration of yttrium element or yttrium ion in the system during sintering can be set within a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal elements or their ions constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency. The method for measuring the monoclinic content is as described in the Examples below.

[0056] In embodiment (A-3), the cubic crystal content is preferably 15% or more, more preferably 18% or more, even more preferably 20% or more, and particularly preferably 25% or more. The cubic crystal content is preferably 44% or less, more preferably 42% or less, even more preferably 40% or less, and particularly preferably 38% or less. The cubic crystal content may be any combination of these ranges. For example, the cubic crystal content is preferably 15% or more and 44% or less, more preferably 15% or more and 42% or less, even more preferably 20% or more and 40% or less, and particularly preferably 25% or more and 38% or less. When the cubic crystal content is within the above range, when combined with monoclinic zirconia, which exists as a destination for yttrium element or yttrium ions, the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set within a desired range, and when combined with a raw material powder having a predetermined average particle size, the stabilizer acts as an integrated body, sufficiently promoting the migration of the metal element or its ion constituting the stabilizer even during a short sintering time of 10 minutes or less, resulting in a zirconia sintered body with excellent translucency. The cubic crystal content can be measured as described in the Examples below.

[0057] In embodiment (A-3), another preferred embodiment is a zirconia calcined body in which a portion of the yttria is not solid-dissolved in zirconia, and the proportion of the yttria not solid-dissolved in zirconia is 1 to 15%.

[0058] In the zirconia calcined body according to embodiment (A-3), the content f of undissolved yttria y can be calculated based on the above formula (2-4).

[0059] In the embodiment (A-3), the content f of undissolved yttria yWhen cubic zirconia and monoclinic zirconia are combined, the concentration gradient of the yttrium element can be set within a desired range, the yttrium element is likely to move even in a short sintering time, and the resulting zirconia sintered body has excellent translucency. Therefore, the content f of undissolved yttria is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 3.5% or more. y is preferably 15% or less in terms of being able to suppress a decrease in strength of the sintered body, and is more preferably 14% or less, even more preferably 12% or less, and particularly preferably 11% or less in terms of being able to reduce the standard deviation of the yttrium element distribution, making it easier for the yttrium element to migrate during short-term sintering, and providing the resulting zirconia sintered body with better translucency. y For example, the content f of undissolved yttria may be in the range of any combination thereof. y is preferably 1 to 15%, more preferably 2 to 14%, even more preferably 3 to 12%, and particularly preferably 3.5 to 11%.

[0060] In embodiment (A-3), the zirconia in the zirconia calcined body may contain a tetragonal system, but preferably does not contain a tetragonal system, since this facilitates the migration of yttrium element or yttrium ions. In other words, in embodiment (A-3), it is preferable that the zirconia calcined body does not simultaneously contain a cubic system and a tetragonal system.

[0061] <Embodiment (A-4)> A preferred embodiment (A-4) is a zirconia calcined body that contains cubic zirconia and monoclinic zirconia, does not fall under (A-3), and has a cubic zirconia content of 15% or more (hereinafter, also referred to as "embodiment (A-4)").

[0062] In embodiment (A-4), the zirconia in the zirconia calcined body contains cubic zirconia. The cubic content is preferably 15% or more, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 40% or more. The cubic content is preferably 98% or less, more preferably 97% or less, even more preferably 96.5% or less, and particularly preferably 96% or less. The cubic content may be any combination of these ranges. For example, the cubic content is preferably 15% or more and 98% or less, more preferably 20% or more and 97% or less, even more preferably 30% or more and 96.5% or less, and particularly preferably 40% or more and 96% or less. When the cubic crystal content is within the above range, when combined with monoclinic zirconia supplied as a destination for yttrium element or yttrium ions, the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set within a desired range, and when combined with a raw material powder having a predetermined average particle size, the stabilizer acts as an integrated body, sufficiently promoting the migration of the metal element or its ion constituting the stabilizer even during a short sintering time of 10 minutes or less, resulting in a zirconia sintered body with excellent translucency. The cubic crystal content can be measured as described in the Examples below.

[0063] In embodiment (A-4), the zirconia in the zirconia calcined body contains monoclinic zirconia. The monoclinic content is preferably 1% or more, more preferably 2% or more, even more preferably 2.5% or more, and particularly preferably 3% or more. The monoclinic content is preferably less than 55%, more preferably 50% or less, even more preferably 45% or less, and particularly preferably 40% or less. The monoclinic content may be any combination of these ranges. For example, the monoclinic content is preferably 1% or more but less than 55%, more preferably 2% or more and 50% or less, even more preferably 2.5% or more and 45% or less, and particularly preferably 3% or more and 40% or less. When the monoclinic content is within the above range, when cubic zirconia, which is a supplier of yttrium element or yttrium ions, is combined with undissolved yttria as needed, the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set within a desired range, and when combined with a raw material powder having a predetermined average particle size, the metal element or its ion constituting the stabilizer acts integrally, and even during a short sintering time of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency. The method for measuring the monoclinic content is as described in the Examples below.

[0064] Another preferred embodiment of embodiment (A-4) is a zirconia calcined body containing cubic zirconia and monoclinic zirconia, in which the cubic zirconia content is 40% or more and 90% or less, and the monoclinic zirconia content is 10% or more and less than 55%.

[0065] Another preferred embodiment of embodiment (A-4) is a zirconia calcined body containing cubic zirconia and monoclinic zirconia, in which the cubic zirconia content is 70% or more and 97% or less, and the monoclinic zirconia content is 3% or more and 30% or less.

[0066] In embodiment (A-4), another preferred embodiment is a zirconia calcined body in which a portion of the yttria is not solid-dissolved in zirconia, and the proportion of the yttria not solid-dissolved in zirconia is 1 to 15%.

[0067] In the zirconia calcined body according to embodiment (A-4), the content f of undissolved yttria y can be calculated based on the above formula (2-4).

[0068] In the embodiment (A-4), the content f of undissolved yttria y When cubic zirconia and monoclinic zirconia are combined, the concentration gradient of the yttrium element can be set within a desired range, the yttrium element is likely to move even in a short sintering time, and the resulting zirconia sintered body has excellent translucency. Therefore, the content f of undissolved yttria is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 3.5% or more. y is preferably 15% or less in terms of being able to suppress a decrease in strength of the sintered body, and is more preferably 14% or less, even more preferably 12% or less, and particularly preferably 11% or less in terms of being able to reduce the standard deviation of the yttrium element distribution, making it easier for the yttrium element to migrate during short-term sintering, and providing the resulting zirconia sintered body with better translucency. y For example, the content f of undissolved yttria may be in the range of any combination thereof. y is preferably 1 to 15%, more preferably 2 to 14%, even more preferably 3 to 12%, and particularly preferably 3.5 to 11%.

[0069] In embodiment (A-4), the zirconia in the zirconia calcined body may contain a tetragonal system, but preferably does not contain a tetragonal system, since this facilitates the migration of yttrium element or yttrium ions. In other words, in embodiment (A-4), it is preferable that the zirconia calcined body does not simultaneously contain a cubic system and a tetragonal system.

[0070] <Embodiment (A-5)> A preferred embodiment (A-5) is a zirconia calcined body in which the zirconia contains tetragonal zirconia and cubic zirconia, the tetragonal content is 5% or more and less than 50%, the cubic content is 50% or more and less than 95%, and part of the yttria is not solid-dissolved in the zirconia (hereinafter, also referred to as "Embodiment (A-5)").

[0071] In embodiment (A-5), the tetragonal content is preferably 6% or more, more preferably 8% or more, even more preferably 9% or more, and particularly preferably 10% or more. The tetragonal content is preferably less than 49%, more preferably less than 48%, even more preferably less than 46%, and particularly preferably less than 40%. The tetragonal content may be any combination of these ranges. For example, in one embodiment, the tetragonal content is preferably 6% or more and less than 49%, more preferably 8% or more and less than 48%, even more preferably 9% or more and less than 46%, and particularly preferably 10% or more and less than 40%. When the tetragonal content is within the above range, when a predetermined content of cubic zirconia is combined with undissolved yttria, the difference in concentration of yttrium element or yttrium ion in the system during sintering can be set within a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal elements or their ions constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency. The method for measuring the tetragonal content is as described in the Examples below.

[0072] In embodiment (A-5), the cubic crystal content is preferably 51% or more, more preferably 52% or more, even more preferably 54% or more, and particularly preferably 60% or more. The cubic crystal content is preferably less than 94%, more preferably less than 92%, even more preferably less than 91%, and particularly preferably less than 90%. The cubic crystal content may be any combination of these ranges. For example, the cubic crystal content is preferably 51% or more and less than 94%, more preferably 52% or more and less than 92%, even more preferably 54% or more and less than 91%, and particularly preferably 60% or more and less than 90%. When the cubic content is within the above range, when undissolved yttria is combined with tetragonal zirconia, which exists as a destination for yttrium element or yttrium ions, the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set within a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during a short sintering time of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency. The cubic content can be measured as described in the Examples below.

[0073] In the embodiment (A-5), a part of the stabilizer among the yttria contained in the zirconia calcined body is undissolved yttria. y can be calculated based on the above formula (2-4).

[0074] In the embodiment (A-5), the content f of undissolved yttria yis preferably 0.001% or more, more preferably 0.01% or more, even more preferably 0.02% or more, particularly preferably 0.05% or more, and most preferably 0.1% or more, from the viewpoints that when cubic zirconia and tetragonal zirconia are combined, the concentration gradient of the yttrium element can be set within a desired range, the yttrium element is likely to move even in a short sintering time, and the resulting zirconia sintered body has excellent translucency. y is preferably 12% or less from the viewpoint of suppressing a decrease in strength of the sintered body, and is more preferably 10% or less, even more preferably 9% or less, particularly preferably 8% or less, and most preferably 5% or less from the viewpoint of reducing the standard deviation of the yttrium element distribution, facilitating the migration of the yttrium element during short-term sintering, and providing the resulting zirconia sintered body with superior translucency. y For example, the content f of undissolved yttria may be in the range of any combination thereof. y is preferably 0.001 to 12%, more preferably 0.01 to 10%, further preferably 0.02 to 9%, particularly preferably 0.05 to 8%, and most preferably 0.1 to 5%.

[0075] In embodiment (A-5), the zirconia in the zirconia calcined body preferably does not contain a monoclinic system, since this facilitates the migration of yttrium element or yttrium ions.

[0076] <Embodiment (A-6)> A preferred embodiment (A-6) is a zirconia calcined body that does not fall under (A-5), in which the zirconia contains tetragonal zirconia and cubic zirconia, the cubic zirconia content is 10% or more and less than 50%, and part of the yttria is not solid-dissolved in the zirconia (hereinafter, also referred to as "Embodiment (A-6)").

[0077] Since embodiment (A-6) does not fall under (A-5), the tetragonal content is 50% or more and less than 90%. In embodiment (A-6), the tetragonal content is preferably 51% or more, more preferably 52% or more, even more preferably 54% or more, and particularly preferably 60% or more. Furthermore, the tetragonal content is preferably less than 89%, more preferably less than 88%, even more preferably less than 86%, and particularly preferably less than 85%. The tetragonal content may be a range that is a combination of any of these ranges. For example, in one embodiment, the tetragonal content is preferably 51% or more and less than 89%, more preferably 52% or more and less than 88%, even more preferably 54% or more and less than 86%, and particularly preferably 60% or more and less than 85%. When the tetragonal content is within the above range, when a predetermined content of cubic zirconia is combined with undissolved yttria, the difference in concentration of yttrium element or yttrium ion in the system during sintering can be set within a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during short sintering times of 10 minutes or less, the migration of the metal elements or their ions constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency. The method for measuring the tetragonal content is as described in the Examples below.

[0078] In embodiment (A-6), the cubic crystal content is preferably 11% or more, more preferably 12% or more, even more preferably 14% or more, and particularly preferably 15% or more. The cubic crystal content is preferably less than 49%, more preferably less than 48%, even more preferably less than 46%, and particularly preferably less than 40%. The cubic crystal content may be any combination of these ranges. For example, the cubic crystal content is preferably 11% or more and less than 49%, more preferably 12% or more and less than 48%, even more preferably 14% or more and less than 46%, and particularly preferably 15% or more and less than 40%. When the cubic content is within the above range, when undissolved yttria is combined with tetragonal zirconia, which exists as a destination for yttrium element or yttrium ions, the difference in concentration of the metal element or its ion constituting the stabilizer in the system during sintering can be set within a desired range, and when combined with a raw material powder having a predetermined average particle size, they act together, and even during a short sintering time of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is sufficiently promoted, resulting in a zirconia sintered body with excellent translucency. The cubic content can be measured as described in the Examples below.

[0079] In the embodiment (A-6), a part of the stabilizer among the yttria contained in the zirconia calcined body is undissolved yttria. y can be calculated based on the above formula (2-4).

[0080] In the embodiment (A-6), the content f of undissolved yttria yis preferably 0.001% or more, more preferably 0.01% or more, even more preferably 0.02% or more, particularly preferably 0.05% or more, and most preferably 0.1% or more, from the viewpoints that when cubic zirconia and tetragonal zirconia are combined, the concentration gradient of the yttrium element can be set within a desired range, the yttrium element is likely to move even in a short sintering time, and the resulting zirconia sintered body has excellent translucency. y is preferably 12% or less from the viewpoint of suppressing a decrease in strength of the sintered body, and is more preferably 10% or less, even more preferably 9% or less, particularly preferably 8% or less, and most preferably 5% or less from the viewpoint of reducing the standard deviation of the yttrium element distribution, facilitating the migration of the yttrium element during short-term sintering, and providing the resulting zirconia sintered body with superior translucency. y For example, the content f of undissolved yttria may be in the range of any combination thereof. y is preferably 0.001 to 12%, more preferably 0.01 to 10%, further preferably 0.02 to 9%, particularly preferably 0.05 to 8%, and most preferably 0.1 to 5%.

[0081] In embodiment (A-6), the zirconia in the zirconia calcined body preferably does not contain a monoclinic system, since this facilitates the migration of yttrium element or yttrium ions.

[0082] In embodiments (A-1) to (A-6), the stabilizer is yttria, and the standard deviation of the yttrium element distribution is 2 mol% or more and less than 21 mol%, so that even in a short sintering time of 10 minutes or less, the movement of yttrium element or yttrium ions between substances in the system during sintering proceeds sufficiently, and the translucency of the obtained zirconia sintered body can satisfy the above formula (1).

[0083] As described above, in view of the ease of obtaining a desired range of standard deviation of elemental yttrium distribution, the zirconia calcined body of the present invention preferably does not include, for example, a zirconia calcined body containing only tetragonal zirconia and cubic zirconia and containing no stabilizer that is not solid-dissolved in the zirconia; a zirconia calcined body containing only cubic zirconia and a stabilizer that is not partly solid-dissolved in the zirconia; a zirconia calcined body containing only cubic zirconia and no stabilizer that is not solid-dissolved in the zirconia; a zirconia calcined body containing monoclinic zirconia and tetragonal zirconia and no stabilizer that is not solid-dissolved in the zirconia; or a zirconia calcined body containing only tetragonal zirconia and no stabilizer that is not solid-dissolved in the zirconia. In one embodiment, the zirconia calcined body may not contain a porosity of 15 to 30%. The porosity is a value calculated from the following formula: Porosity (%) = Pore volume / (Pore volume + Skeleton volume) x 100 The pore volume is a value determined by measuring the number of interconnected pores, which do not contain closed pores, having a diameter of about 5 nm to 250 μm, by mercury intrusion porosimetry. The skeletal volume is a value calculated from the true density measured by gas phase displacement spectroscopy. The skeletal volume is the skeletal volume (cm 3 / g) = 1 / true density (g / cm 3 The pore volume and skeletal volume were measured using a sample of calcined zirconia cut into a rectangular column (5 mm × 5 mm × 5 mm). The pore volume was measured using a fully automatic multifunctional mercury porosimeter (POREMASTER, manufactured by Anton Paar Japan Co., Ltd.) (measurement conditions: mercury surface tension: 480 erg / cm 2 , contact angle: 140°, discharge contact angle: 140°, pressure: 0 to 50,000 psia), and the skeletal volume can be calculated by measuring the true density using a dry automatic densimeter (AccuPic II 1340, manufactured by Shimadzu Corporation).

[0084] The density of the zirconia calcined body of the present invention is 3.6 g / cm 3 Preferably, it is 3.5 g / cm or less. 3More preferably, it is 3.4 g / cm or less. 3 The density of the zirconia calcined body of the present invention is more preferably 2.5 g / cm or less. 3 It is preferable that the density is 2.7 g / cm or more. 3 More preferably, it is 2.9 g / cm or more. 3 More preferably, it is equal to or greater than this.

[0085] The density of the zirconia calcined body can be calculated by (mass of the zirconia calcined body) / (volume of the zirconia calcined body). The density of the zirconia calcined body can be determined, for example, by cutting out 10 mm square specimens (n=3) from arbitrary positions on the zirconia calcined body while changing the cutting position, measuring the mass and volume of the obtained specimens, calculating the average of the measured values, and using the average value to calculate the density according to the above formula.

[0086] The average primary particle size of the particles in the zirconia calcined body of the present invention is preferably 40 nm or more, more preferably 45 nm or more, and even more preferably 50 nm or more. The average primary particle size of the particles in the zirconia calcined body of the present invention is preferably 110 nm or less, more preferably 105 nm or less, and even more preferably 100 nm or less. The average primary particle size of the particles in the zirconia calcined body may be any combination of these ranges. For example, the average primary particle size is preferably 40 to 110 nm, more preferably 45 to 105 nm, and even more preferably 50 to 100 nm.

[0087] The method for measuring the average primary particle size of the particles in the zirconia calcined body is as described in the Examples below.

[0088] The zirconia calcined body of the present invention may 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), binders, dispersants, emulsifiers, antifoaming agents, pH adjusters, lubricants, and translucency adjusters. One type of additive may be used alone, or two or more types may be used in combination.

[0089] Examples of the pigment include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Er.

[0090] Examples of the composite pigment include (Zr, V) O 2 , Fe(Fe, Cr) 2 O 4 , (Ni, Co, Fe)(Fe, Cr) 2 O 4 .ZrSiO 4 , and (Co, Zn)Al 2 O 4 .

[0091] The zirconia calcined body of the present invention may contain a fluorescent agent. By including a fluorescent agent in the zirconia calcined body, the zirconia sintered body has fluorescence. The type of fluorescent agent is not particularly limited, and one or more fluorescent agents capable of emitting fluorescence with light of any wavelength can be used. Examples of fluorescent agents include those containing metal elements. Examples of such metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one of these metal elements alone, or two or more of them. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred. Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the above metal elements. The fluorescent agents are Y2SiO5:Ce, Y2SiO5:Tb, (Y, Gd, Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl. 10 O 17 :Eu, etc.

[0092] The content of the fluorescent agent in the zirconia calcined body is not particularly limited and can be adjusted appropriately depending on the type of fluorescent agent or the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the fluorescent agent content is preferably 0.001 mass% or more, more preferably 0.005 mass% or more, and even more preferably 0.01 mass% or more, calculated as the oxide of the metal element contained in the fluorescent agent, relative to 100 mass% of zirconia contained in the zirconia calcined body. Furthermore, the fluorescent agent content is preferably 1 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less, calculated as the oxide of the metal element contained in the fluorescent agent. When the content is above the lower limit, the fluorescence is comparable to that of natural human teeth. When the content is below the upper limit, the decrease in translucency and mechanical strength can be suppressed.

[0093] Examples of binders include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic binders, wax-based binders, polyvinyl butyral, polymethyl methacrylate, ethyl cellulose, etc. In order to improve translucency, the content of the binder in the zirconia composition of the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, relative to 100% by mass of zirconia.

[0094] Examples of the plasticizer include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0095] Examples of dispersants include ammonium polycarboxylate (e.g., triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic acid ester copolymer, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (e.g., polyoxyethylene alkyl ether phosphate esters such as polyoxyethylene lauryl ether phosphate esters), nonionic surfactants, olein glyceride, amine salt surfactants, oligosaccharide alcohols, and stearic acid.

[0096] Examples of emulsifiers include alkyl ethers, phenyl ethers, sorbitan derivatives, and ammonium salts.

[0097] Examples of the antifoaming agent include alcohol, polyether, polyethylene glycol, silicone, and wax.

[0098] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide).

[0099] Examples of the lubricant include polyoxyethylene alkylate ether and wax.

[0100] Examples of the light transmittance adjusting agent include aluminum oxide (Al2O3), titanium oxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0101] [Method for producing zirconia calcined body] The zirconia calcined body of the present invention can be produced by firing (calcining) a zirconia composition (e.g., a molded body) to a degree that does not result in sintering of the zirconia particles. In this specification, the zirconia composition is a composition containing zirconia powder and a powder of a stabilizer capable of suppressing the phase transition of zirconia. The zirconia composition may be, for example, a molded body. The molded body is formed by applying an external force to a powder containing zirconia-based particles. The zirconia composition and zirconia molded body are those before firing, and therefore do not exhibit necking (sticking).

[0102] One embodiment is a zirconia composition containing zirconia and a stabilizer capable of suppressing a phase transition of zirconia, wherein, when ΔL1*(W-B) of a first sintered body produced by sintering the zirconia composition at 1550°C for 120 minutes is compared with ΔL2*(W-B) of a second sintered body produced by sintering the zirconia composition at 1550°C for 10 minutes, the zirconia composition satisfies the following formula (1): ΔL2*(W-B) / ΔL1*(W-B)≧0.85 (1) ΔL1*(W-B) and ΔL2*(W-B) are as described for the zirconia calcined body.

[0103] By calcining the zirconia composition, organic substances are removed, a desired amount of stabilizer is dissolved in the zirconia, and a calcined zirconia body in which the primary particles are necked is obtained.

[0104] The temperature at which the zirconia composition is fired (calcination temperature) is preferably 200°C or higher, more preferably 300°C or higher, and even more preferably 400°C or higher, from the viewpoints of obtaining excellent translucency in a short time in the subsequent sintering step, being able to remove organic substances, and not adversely affecting the subsequent sintering step. Furthermore, the calcination temperature is preferably 900°C or lower, more preferably 700°C or lower, and even more preferably 600°C or lower. The calcination temperature may be within any combination of these ranges. For example, the calcination temperature is preferably 200 to 900°C, more preferably 300 to 700°C, and even more preferably 400 to 600°C. The pressure during calcination is not particularly limited and may be atmospheric pressure.

[0105] The time for treatment at the calcination temperature (calcination time) is preferably 30 minutes or more, more preferably 120 minutes or more. By setting the calcination time to 120 minutes or more, organic substances can be removed and adverse effects in the subsequent sintering step can be easily avoided. Furthermore, the calcination time is preferably 360 minutes or less, more preferably 240 minutes or less. Setting the calcination time to 240 minutes or less is preferable because it reduces the diffusion distance of the stabilizer and maintains the concentration gradient of the stabilizer, thereby achieving excellent translucency in a short time in the subsequent sintering step. The calcination time may be set to any combination of these ranges. For example, the calcination time is preferably 30 to 360 minutes, more preferably 120 to 240 minutes.

[0106] [Method for Producing Zirconia Composition] Examples of methods for producing a zirconia composition include a step of producing a zirconia powder, a step of producing a powder of a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also referred to as "stabilizer powder"), and a step of mixing the zirconia powder and the stabilizer powder to produce a powder containing zirconia-based particles. In this specification, particles containing zirconia particles and stabilizer particles are referred to as "zirconia-based particles."

[0107] - Method for producing zirconia powder and stabilizer powder There are no particular limitations on the method for preparing the raw material powders, zirconia powder and yttria powder. For example, a breakdown process in which coarse particles are pulverized or crushed to produce fine powder, or a building-up process in which atoms or ions are synthesized through a nucleation and growth process can be used.

[0108] Examples of the zirconia powder include tetragonal zirconia powder (T), monoclinic zirconia powder (M), and cubic zirconia powder (C).

[0109] The average primary particle size (r1) of the zirconia powder (hereinafter also referred to as "average particle size (r1)") is preferably 40 nm or more, more preferably 45 nm or more, and even more preferably 50 nm or more, in order to ensure excellent translucency of the zirconia calcined body obtained by short-time sintering. Furthermore, the average particle size (r1) of the zirconia powder is preferably 110 nm or less, more preferably 105 nm or less, and even more preferably 100 nm or less, in order to ensure excellent translucency of the zirconia calcined body obtained by short-time sintering. The average particle size (r1) of the zirconia powder may be any combination of these ranges. For example, the average particle size (r1) of the zirconia powders (zirconia powder (T), zirconia powder (C), and zirconia powder (M)) is preferably 40 to 110 nm, more preferably 45 to 105 nm, and even more preferably 50 to 100 nm. When the average particle diameters of the tetragonal zirconia powder (T), the monoclinic zirconia powder (M), and the cubic zirconia powder (C) are within the range of the average particle diameter (r1), when a specific crystal system is selected and used, the migration of the metal elements or ions thereof constituting the stabilizer is sufficiently promoted even during short-term sintering of 10 minutes or less, and the resulting zirconia sintered body has excellent translucency.

[0110] The average primary particle diameter (r2) of the stabilizer powder capable of suppressing the phase transition of zirconia (hereinafter also referred to as "average particle diameter (r2)") is preferably 20 nm or more, more preferably 40 nm or more, even more preferably 45 nm or more, and particularly preferably 50 nm or more, in order to ensure excellent translucency of the zirconia calcined body obtained by short-time sintering. Furthermore, the average particle diameter (r2) of the stabilizer powder is preferably 350 nm or less, more preferably 300 nm or less, even more preferably 250 nm or less, and particularly preferably 200 nm or less, in order to ensure excellent translucency of the zirconia calcined body obtained by short-time sintering. The average particle diameter (r2) of the stabilizer powder may be any combination of these ranges. For example, the average particle diameter (r1) of the zirconia powder is preferably 20 to 350 nm, more preferably 40 to 300 nm, even more preferably 45 to 250 nm, particularly preferably 50 to 200 nm, and most preferably 60 to 110 nm. When the average particle size (r2) of the stabilizer powder is within the above range, when the stabilizer powder is combined with a zirconia powder having a specific crystal system and the above-mentioned predetermined average particle size (r1), the migration of the metal elements or ions constituting the stabilizer is sufficiently promoted even during short-time sintering of 10 minutes or less, and the resulting zirconia sintered body has excellent translucency.

[0111] In some embodiments, the stabilizer powder may have an average particle size (r2) of greater than 60 nm, such as a zirconia composition having an average particle size (r2) of greater than 60 nm and equal to or less than 300 nm.

[0112] The average particle size (r1) and the average particle size (r2) are average primary particle sizes, and can be measured on a volume basis using, for example, a laser diffraction / scattering particle size distribution measuring device (product name "Partica LA-950") manufactured by Horiba, Ltd., by irradiating a slurry diluted with water with ultrasonic waves for 30 minutes, and then applying ultrasonic waves.

[0113] The following describes an example of a method for preparing zirconia powder. The method for preparing zirconia powder can also be used for preparing stabilizer particles, unless otherwise specified.

[0114] A preferred embodiment is a zirconia composition that satisfies either of the following conditions (i) or (ii): (i) the zirconia is a stabilizer powder containing a tetragonal zirconia powder (T) and a part of the stabilizer is not solid-dissolved in the zirconia; or (ii) the zirconia is a monoclinic zirconia powder (M) and a cubic zirconia powder (C).

[0115] Suitable embodiments that satisfy the condition (i) include, for example, a zirconia composition containing only tetragonal zirconia powder (T) and a stabilizer powder in which part of the stabilizer is not dissolved in the zirconia; a zirconia composition containing monoclinic zirconia powder (M) and tetragonal zirconia powder (T) and a stabilizer powder in which part of the stabilizer is not dissolved in the zirconia; and a zirconia composition containing tetragonal zirconia powder (T) and cubic zirconia powder (C) and a stabilizer powder in which part of the stabilizer is not dissolved in the zirconia. Another suitable embodiment is a zirconia composition that satisfies the condition (i) and further contains monoclinic zirconia powder (M).

[0116] Another preferred embodiment is a zirconia composition that satisfies the condition (ii) and further includes a zirconia composition in which a part of the stabilizer is not solid-dissolved in zirconia.

[0117] As the zirconia raw material used to produce the zirconia powder, tetragonal zirconia, monoclinic zirconia, and cubic zirconia can be used. These zirconia raw materials can be produced, for example, by the production method described in Japanese Patent No. 6543926 (produced by hydrolysis). Commercially available zirconia raw materials can also be used. Examples of commercially available products include zirconia powder "TZ-0" (monoclinic 0Y (0 mol % yttria)), 3 mol % yttria solid-solution zirconia powder "TZ-3Y-E" (tetragonal 3Y), 6 mol % yttria solid-solution zirconia powder "TZ-6Y" (cubic 6Y), and 10 mol % yttria solid-solution zirconia powder "TZ-10Y" (cubic 10Y), all of which are manufactured by Tosoh Corporation.

[0118] In the breakdown process, coarse particles of the zirconia raw material are separately pulverized according to their crystal systems to produce tetragonal zirconia powder (T), monoclinic zirconia powder (M), and cubic zirconia powder (C), each adjusted to fall within the above-mentioned range of average particle size (r2). Furthermore, in terms of ease of controlling the desired average particle sizes (r1) and (r2), it is preferable to produce the zirconia powder by pulverizing the zirconia raw material separately from the raw material of the stabilizer powder (e.g., yttria raw material).

[0119] The stabilizer powder can also be adjusted to the average particle size (r2) by pulverizing a raw material compound (e.g., yttria) by a known method (e.g., ball mill). The average particle size of the raw material compound is not particularly limited as long as it can be adjusted to fall within the range of the average particle size (r2) by pulverization.

[0120] The average particle size of the zirconia powder having the above average particle size (r1) and the stabilizer powder having the above average particle size (r2) can be adjusted by known methods, such as grinding the raw material powder. Because it is easy to adjust the above-mentioned predetermined average particle size (r1) and average particle size (r2), it is preferable to use fine-sized grinding media for grinding, for example, grinding media of 100 μm or less. Furthermore, it is preferable to classify the resulting zirconia powder after grinding the coarse particles. Known methods and devices can be used for classification. Known methods include, for example, elutriation (elutriation) utilizing differences in sedimentation velocity due to particle size-dependent dispersibility, and then accelerating the sedimentation using a centrifuge. Known devices include, for example, porous membranes (e.g., membrane filters with pores of 100 nm), classification devices (wet classification devices, dry classification devices), etc. A raw material powder having the desired average particle size can be obtained by operations such as grinding and classification, including changing the grinding time as necessary. By preparing a raw material powder having a desired average particle size, when a predetermined crystal system and / or undissolved yttria is selected for the zirconia crystal system, the concentration gradient of elemental yttrium or yttrium ions can be easily controlled within a predetermined range. As a result, mass transfer occurs while particles are solidifying together during sintering, and the migration of elemental yttrium or yttrium ions progresses sufficiently even in a short sintering time of 10 minutes or less. This results in a more uniform distribution of elemental yttrium in the resulting zirconia sintered body, and it is believed that the translucency of the zirconia sintered body satisfies the above formula (1).

[0121] In addition, the following description will be given taking the case where the stabilizer is yttria as an example, but the present invention is not limited to the case where the stabilizer is yttria. As a zirconia raw material, the content of dissolved yttria in tetragonal zirconia (hereinafter also referred to as the "amount of dissolved yttria") is preferably 2 mol% or more, more preferably 2.2 mol% or more, and even more preferably 2.5 mol% or more, relative to the total moles of zirconia and yttria. Furthermore, the amount of dissolved yttria in the tetragonal zirconia is preferably less than 5 mol%, more preferably 4.8 mol% or less, even more preferably 4.5 mol% or less, particularly preferably 4.0 mol% or less, and most preferably 3.8 mol% or less. The amount of dissolved yttria in the tetragonal zirconia may be within any of these ranges. For example, the amount of yttria dissolved in the tetragonal zirconia is preferably 2 mol% or more and less than 5 mol%, more preferably 2.0 mol% or more and 4.8 mol% or less, even more preferably 2.2 mol% or more and 4.5 mol% or less, particularly preferably 2.2 mol% or more and 4.0 mol% or less, and most preferably 2.5 mol% or more and 3.8 mol% or less. The amount of yttria dissolved in the tetragonal zirconia powder (T) obtained from the zirconia raw material is also similar to the amount of yttria dissolved in the zirconia raw material.

[0122] The amount of yttria dissolved in the monoclinic zirconia used in the present invention is preferably 0 to 1 mol %, more preferably 0 to 0.5 mol %, and even more preferably 0 mol %, relative to the total moles of zirconia and yttria. The amount of yttria dissolved in the monoclinic zirconia powder (M) obtained from the zirconia raw material is also similar to the amount of yttria dissolved in the zirconia raw material.

[0123] As a zirconia raw material, the amount of yttria dissolved in cubic zirconia is preferably 5 mol% or more, more preferably 5.5 mol% or more, and even more preferably 6 mol% or more, based on the total moles of zirconia and yttria. Furthermore, the amount of yttria dissolved in the cubic zirconia is preferably 15 mol% or less, more preferably 12 mol% or less, and even more preferably 10 mol% or less. The amount of yttria dissolved in the cubic zirconia may be any combination of these ranges. For example, the amount of yttria dissolved in the cubic zirconia is preferably more than 5 mol% and 15 mol% or less, more preferably 5.5 mol% to 12 mol%, and even more preferably 6 mol% to 10 mol%. The amount of yttria dissolved in the cubic zirconia powder (C) obtained from the zirconia raw material is the same as the amount of yttria dissolved in the zirconia raw material.

[0124] The amount of yttria dissolved in tetragonal, monoclinic, and cubic zirconia can be measured by, for example, inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis (XRF), or the like.

[0125] The zirconia composition of the present invention may 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), binders, dispersants, emulsifiers, antifoaming agents, pH adjusters, lubricants, alumina (Al2O3), titanium oxide (TiO2), and silica (SiO2). One type of additive may be used alone, or two or more types may be used in combination. Examples of additives include those listed for the zirconia calcined body. The additives may be added during mixing or pulverization of the raw materials, or may be added to the pulverized powder.

[0126] In the production of the zirconia composition of the present invention, the zirconia powder and the stabilizer powder may be mixed by dry mixing or wet mixing.

[0127] The mixing ratio of the zirconia powder and the stabilizer powder can be adjusted appropriately depending on the embodiment (for example, embodiments (A-1) to (A-6) etc.) so as to obtain the desired content of the crystal system.

[0128] For example, in a zirconia composition satisfying condition (i), when a monoclinic zirconia powder (M) is further contained as needed, the ratio of the total mass of the zirconia powder (T) and the zirconia powder (M) to the mass of the stabilizer powder is preferably 85.0% by mass:15.0% by mass to 99.8% by mass:0.2% by mass. In addition, in a zirconia composition satisfying condition (i), the respective contents of the zirconia powder (T) and the zirconia powder (M) can be adjusted within the above ranges so as to obtain the tetragonal content and monoclinic content in embodiments (A-1) and (A-2). In addition, in an embodiment, when a zirconia composition satisfying condition (i) contains a zirconia powder (M) as in embodiments (A-1) and (A-2), the content of the zirconia powder (M) in the zirconia composition is preferably 0 to 85 mass%, more preferably 0 to 82 mass%, and even more preferably 0 to 80 mass%, of the total mass of the zirconia powder (T) and the zirconia powder (M).

[0129] A zirconia composition satisfying condition (i) preferably contains a zirconia powder (T) containing a stabilizer capable of suppressing the phase transition of dissolved zirconia. The content of the stabilizer capable of suppressing the phase transition of dissolved zirconia in the zirconia powder (T) is preferably 2 to 4 mol%, more preferably 2 to 3.5 mol%, and even more preferably 2 to 3 mol%, based on the total moles of zirconia and stabilizer.

[0130] In a zirconia composition satisfying condition (ii), the ratio of the total mass of the zirconia powder (M) and the zirconia powder (C) to the mass of the stabilizer powder is preferably 85.0% by mass:15.0% by mass to 100% by mass:0% by mass. In a zirconia composition satisfying condition (ii), the respective contents of the zirconia powder (M) and the zirconia powder (C) can be adjusted within the above ranges so as to obtain the monoclinic content and cubic content in embodiments (A-3) and (A-4).

[0131] In one embodiment, the content of the zirconia powder (C) in the zirconia composition satisfying the condition (ii) is preferably 15.0 to 95.0 mass%, more preferably 18.0 to 82.0 mass%, and even more preferably 20.0 to 80.0 mass%, of the total mass of the zirconia powder (M) and the zirconia powder (C).

[0132] In a zirconia composition satisfying the condition (ii), the content of the stabilizer capable of suppressing the phase transition of dissolved zirconia in the zirconia powder (M) is preferably 0 to 1 mol %, more preferably 0 to 0.5 mol %, and even more preferably 0 mol %, relative to the total moles of zirconia and the stabilizer.

[0133] In a zirconia composition satisfying the condition (ii), the content of the stabilizer capable of suppressing the phase transition of dissolved zirconia in the zirconia powder (C) is preferably 5 mol % or more and 15 mol % or less, more preferably 5.5 mol % or more and 12 mol % or less, and even more preferably 6 mol % or more and 10 mol % or less, based on the total moles of zirconia and the stabilizer.

[0134] Furthermore, in the zirconia composition satisfying the condition (i), when a cubic zirconia powder (T) is further contained as necessary, the ratio of the total mass of the zirconia powder (T) and the zirconia powder (C) to the mass of the stabilizer powder is preferably 88.0 mass%:12.0 mass% to 99.999 mass%:0.001 mass%, more preferably 90.0 mass%:10.0 mass% to 99.99 mass%:0.01 mass%, even more preferably 91.0 mass%:9.0 mass% to 99.98 mass%:0.02 mass%, particularly preferably 92.0 mass%:8.0 mass% to 99.95 mass%:0.05 mass%, and most preferably 95.0 mass%:5.0 mass% to 99.9 mass%:0.1 mass%. Furthermore, in the case where the zirconia composition satisfying the condition (i) further contains a cubic zirconia powder (T) as necessary, the respective contents of the zirconia powder (T) and the zirconia powder (C) can be adjusted within the above-mentioned ranges so as to obtain the tetragonal content and the cubic content in the embodiments (A-5) and (A-6).

[0135] The solvent used in the wet mixing is not particularly limited as long as it contains water, and an organic solvent, a mixed solvent of water and an organic solvent, or water alone may be used. Examples of organic solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, 2-methoxyethanol, 2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol, diethylene glycol monobutyl ether, and glycerin; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, diethyl ether, diisopropyl ether, 1,4-dioxane, and dimethoxyethane (including modified ethers such as propylene glycol monomethyl ether acetate (commonly known as "PGMEA") (preferably ether-modified ethers and / or ester-modified ethers, more preferably ether-modified alkylene glycols and / or ester-modified alkylene glycols)); esters such as ethyl acetate and butyl acetate; hydrocarbons such as hexane and toluene; and halogenated hydrocarbons such as chloroform and carbon tetrachloride. The organic solvent may be used alone or in combination of two or more kinds.

[0136] The zirconia composition of the present invention may be in a dry state, or may contain or be contained in a liquid. For example, the zirconia composition may be in the form of a powder, a paste, a slurry, or the like.

[0137] The method for wet-mixing the raw materials in a solvent containing water is not particularly limited. For example, the raw materials may be wet-pulverized and mixed in a known pulverizing and mixing device (such as a ball mill) to form a slurry containing zirconia-based particles, and then the slurry containing the zirconia-based particles may be dried and granulated to produce a granular zirconia composition.

[0138] The mixed powder obtained by mixing the zirconia powder and the stabilizer powder is also referred to as "powder containing zirconia-based particles" below.

[0139] When the slurry is dried to granulate it, the drying method is not particularly limited, and for example, spray drying, supercritical drying, freeze drying, hot air drying, reduced pressure drying, etc. can be used. Among these, any of spray drying, supercritical drying, and freeze drying is preferred, any of spray drying and supercritical drying is more preferred, and spray drying is even more preferred, because it is possible to suppress aggregation of particles during drying and obtain a denser zirconia sintered body.

[0140] The slurry containing zirconia-based particles to be dried may be a slurry in which the dispersion medium is water, but it is preferable that the slurry be a slurry in which the dispersion medium is other than water, such as an organic solvent, because this makes it possible to suppress aggregation of particles during drying and thereby obtain a denser zirconia sintered body.

[0141] The water content of the slurry containing zirconia-based particles to be dried is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, because this can suppress particle aggregation during drying and allow a denser zirconia sintered body to be obtained. The water content can be measured using a Karl Fischer moisture meter.

[0142] The drying conditions for each drying method are not particularly limited, and known drying conditions can be appropriately adopted. When an organic solvent is used as the dispersion medium, drying is preferably carried out in the presence of a non-flammable gas, more preferably in the presence of nitrogen, in order to reduce the risk of explosion during drying.

[0143] The supercritical fluid used in supercritical drying is not particularly limited, and for example, water, carbon dioxide, etc. can be used. However, it is preferable that the supercritical fluid is carbon dioxide, since this can suppress aggregation of particles and thereby produce a denser zirconia sintered body.

[0144] Furthermore, particularly when spray drying is employed, it is preferable that the dispersion medium of the slurry containing zirconia-based particles to be dried contains a liquid having a surface tension of 50 mN / m or less at 25° C., since this can suppress aggregation of the zirconia particles during drying and allows for the production of a denser zirconia sintered body. From this perspective, the surface tension of the liquid is preferably 40 mN / m or less, and more preferably 30 mN / m or less.

[0145] The surface tension at 25°C can be measured using, for example, the values ​​described in the Handbook of Chemistry and Physics. For liquids not described therein, the values ​​described in WO 2014 / 126034 can be used. For liquids not described in any of these publications, the surface tension can be determined by known measurement methods, such as the hanging ring method or the Wilhelmy method. The surface tension at 25°C is preferably measured using an automatic surface tensiometer "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. or a "SIGMA 702" manufactured by KSV INSTRUMENTS LTD (now Biolin Scientific AB, Sweden).

[0146] As the liquid, an organic solvent having the above-mentioned surface tension can be used. As the organic solvent, any of the above-mentioned organic solvents having the above-mentioned surface tension can be used, but at least one selected from the group consisting of methanol, ethanol, 2-methoxyethanol, 1,4-dioxane, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol is preferred, and at least one selected from the group consisting of methanol, ethanol, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol is more preferred, because it can suppress aggregation of particles during drying and thereby produce a denser zirconia sintered body.

[0147] The content of the liquid in the dispersion medium is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, because this makes it possible to suppress aggregation of particles during drying and to obtain a denser zirconia sintered body.

[0148] A slurry containing a dispersion medium other than water can be obtained by substituting the dispersion medium for a slurry containing water. There are no particular limitations on the method for substituting the dispersion medium. For example, a method can be employed in which a dispersion medium other than water (such as an organic solvent) is added to a slurry containing water, and then the water is distilled off. When distilling off the water, part or all of the dispersion medium other than water may be distilled off together. The addition of the dispersion medium other than water and the distillation off of the water may be repeated multiple times. Alternatively, a method can be employed in which a dispersion medium other than water is added to a slurry containing water, and then the dispersoid is precipitated. Furthermore, the dispersion medium of a slurry containing water may be substituted with a specific organic solvent, and then further substituted with another organic solvent.

[0149] The fluorescent agent may be added after replacing the dispersion medium, but is preferably added before replacing the dispersion medium, because a more uniform zirconia sintered body with excellent physical properties can be obtained. Similarly, when a colorant and / or a light-transmittance adjuster is contained in the slurry, the fluorescent agent may be added after replacing the dispersion medium, but is preferably added before replacing the dispersion medium, because a more uniform zirconia sintered body with excellent physical properties can be obtained.

[0150] On the other hand, examples of the build-up process include a gas-phase pyrolysis method in which an oxide is precipitated by thermally decomposing an oxyacid salt of a metal ion or an organometallic compound while vaporizing it; a gas-phase reaction method in which synthesis is carried out by a gas-phase chemical reaction between a gas of a metal compound with a high vapor pressure and a reactive gas; an evaporation concentration method in which a raw material is heated and vaporized, and then rapidly cooled in an inert gas at a predetermined pressure to condense the vapor into fine particles; a melt method in which a molten liquid is cooled into small droplets and solidified to form a powder; a solvent evaporation method in which a solvent is evaporated to increase the concentration in the liquid to a supersaturated state, and then precipitation is carried out; and a precipitation method in which the solute concentration is supersaturated by reaction with a precipitant or hydrolysis, and sparingly soluble compounds such as oxides and hydroxides are precipitated through a nucleation-growth process.

[0151] Precipitation methods are further classified into homogeneous precipitation methods, in which a precipitant is generated in a solution by a chemical reaction to eliminate local non-uniformity in the precipitant concentration; coprecipitation methods, in which multiple metal ions coexisting in a solution are simultaneously precipitated by adding a precipitant; hydrolysis methods, in which an oxide or hydroxide is obtained by hydrolysis from a metal salt solution or an alcohol solution of a metal alkoxide or the like; and solvothermal synthesis methods, in which an oxide or hydroxide is obtained from a high-temperature, high-pressure fluid. The solvothermal synthesis methods are further classified into hydrothermal synthesis methods using water as a solvent and supercritical synthesis methods using a supercritical fluid such as water or carbon dioxide as a solvent. Note that in the present invention, it is preferable not to use a coprecipitation method using zirconia and a stabilizer, in order to ensure that the particles of the zirconia powder and stabilizer powder have the desired average particle sizes (r1) and (r2).

[0152] The zirconium source used in the build-up process may be, for example, a nitrate, an acetate, a chloride, an alkoxide, etc. Specific examples of the zirconium source include zirconium oxychloride, zirconium acetate, and zirconyl nitrate.

[0153] The zirconia powder may be used in the step of mixing the zirconia powder and the stabilizer powder in the form of a slurry containing zirconia particles without drying, as long as the average particle size of the zirconia particles is within the desired range when produced by a method such as a building-up process. The method for preparing the slurry containing zirconia particles is not particularly limited, and it may be obtained, for example, via the breakdown process or building-up process described above.

[0154] When the zirconia composition of the present invention is in a dry state, it can be obtained by drying a slurry containing zirconia particles.

[0155] The zirconia composition of the present invention may be formed into a molded body through a molding process. The term "molded body" refers to a body that has not yet reached either a semi-sintered state (calcined state) or a sintered state. In other words, the molded body is distinguished from a calcined body and a sintered body in that the molded body is formed into a molded body and then unsintered.

[0156] The type of the molding step is not particularly limited, but because the zirconia molded body of the present invention, and therefore the zirconia calcined body and zirconia sintered body of the present invention, can be easily obtained, the molding step is preferably at least one of: (i) a step of slip-casting a slurry containing zirconia-based particles; (ii) a step of gel-casting a slurry containing zirconia-based particles; (iii) a step of press-molding a powder containing zirconia-based particles; (iv) a step of molding a composition containing zirconia-based particles and a resin; (v) a step of polymerizing a composition containing zirconia-based particles and a polymerizable monomer or oligomer; and (vi) a step of layer-by-layer manufacturing of granules containing zirconia-based particles, and more preferably a method having a molding step of molding zirconia-based particles, a polyol, and a binder to obtain a zirconia molded body.

[0157] (i) Slip Casting When a zirconia molded body is produced by a method including a step of slip-casting a slurry containing zirconia-based particles, the specific method of slip-casting is not particularly limited. For example, a method can be employed in which a slurry containing zirconia-based particles is poured into a mold and then dried.

[0158] The content of the dispersion medium in the slurry containing the zirconia-based particles used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, because this allows the slurry to be easily poured into a mold, prevents a long drying time from being required, and enables the number of times the mold can be used to be increased.

[0159] The slurry may be poured into the mold under normal pressure, but from the viewpoint of production efficiency, it is preferable to pour the slurry under pressurized conditions. There are no particular limitations on the type of mold used in slip casting, and for example, porous molds made of gypsum, resin, ceramics, etc. can be used. Porous molds made of resin or ceramics are excellent in terms of durability.

[0160] The zirconia-based particle-containing slurry used in slip casting may further contain one or more of the above-mentioned other components, such as a binder, a plasticizer, a dispersant, an emulsifier, an antifoaming agent, a pH adjuster, and a lubricant.

[0161] (ii) Gel Casting When a zirconia molded body is produced by a method including a step of gel-casting a slurry containing zirconia-based particles, the specific method of gel-casting is not particularly limited. For example, a method can be employed in which a shaped wet body is obtained by gelling a slurry containing zirconia particles and a fluorescent agent in a mold, and then the obtained wet body is dried.

[0162] The content of the dispersion medium in the slurry containing the zirconia-based particles used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, because this can prevent drying from taking a long time and can also suppress the occurrence of cracks during drying.

[0163] The gelation may be carried out, for example, by adding a gelling agent, or by adding a polymerizable monomer and then polymerizing it. There are no particular limitations on the type of mold used, and for example, a porous mold made of gypsum, resin, ceramics, etc., or a non-porous mold made of metal, resin, etc., can be used.

[0164] There is no limitation on the type of gelling agent, and for example, a water-soluble gelling agent can be used, and specifically, agarose, gelatin, etc. can be preferably used. A single gelling agent may be used alone, or two or more types may be used in combination. The amount of gelling agent used is not particularly limited as long as problems such as cracking do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less based on the mass of the slurry after the gelling agent is blended.

[0165] The type of polymerizable monomer is not particularly limited, and examples thereof include (meth)acrylate monomers such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; and (meth)acrylamide monomers such as N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N,N-bis(2-hydroxyethyl) (meth)acrylamide. One type of polymerizable monomer may be used alone, or two or more types may be used in combination.

[0166] The amount of polymerizable monomer used is not particularly limited as long as problems such as cracks do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less, based on the mass of the slurry after the polymerizable monomer is blended.

[0167] When gelation is carried out by polymerization of a polymerizable monomer, the polymerization is preferably carried out using a polymerization initiator. There are no particular restrictions on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred.

[0168] Specific examples of the photopolymerization initiator include (bis)acylphosphine oxides (including salts), thioxanthones (including salts such as quaternary ammonium salts), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ether compounds, and α-aminoketone compounds. One photopolymerization initiator may be used alone, or two or more may be used in combination. Among these photopolymerization initiators, it is preferable to use at least one selected from the group consisting of (bis)acylphosphine oxides and α-diketones. This allows polymerization (gelation) to occur in both the ultraviolet (including near-ultraviolet) and visible light regions, and in particular, polymerization (gelation) can be sufficiently performed using any light source, such as a laser (e.g., Ar laser, He—Cd laser), or lighting (e.g., halogen lamp, xenon lamp, metal halide lamp, light-emitting diode (LED), mercury lamp, or fluorescent lamp.

[0169] Among the (bis)acylphosphine oxides, examples of the acylphosphine oxides include 2,4,6-trimethylbenzoyldiphenylphosphine oxide (commonly known as "TPO"), 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide, 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide, 2,3,5,6-tetramethylbenzoyldiphenylphosphine oxide, benzoyldi(2,6-dimethylphenyl)phosphonate, sodium salt of 2,4,6-trimethylbenzoylphenylphosphine oxide, potassium salt of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and ammonium salt of 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0170] Of the (bis)acylphosphine oxides, examples of the bisacylphosphine oxides include bis(2,6-dichlorobenzoyl)phenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, bis(2,6-dimethoxybenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and bis(2,3,6-trimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide. Furthermore, compounds described in JP-A No. 2000-159621 can also be used.

[0171] Among these (bis)acylphosphine oxides, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and sodium salts of 2,4,6-trimethylbenzoylphenylphosphine oxide are preferred.

[0172] Examples of α-diketones include diacetyl, benzyl, camphorquinone, 2,3-pentadione, 2,3-octadione, 9,10-phenanthrenequinone, 4,4′-oxybenzyl, acenaphthenequinone, etc. Among these, camphorquinone is preferred, particularly when a light source in the visible light region is used.

[0173] The zirconia-based particle-containing slurry used in gel casting may also contain one or more of the above-mentioned other components, such as binders, plasticizers, dispersants, emulsifiers, antifoaming agents, pH adjusters, and lubricants, as in the case of slurries used in slip casting.

[0174] The drying method for drying the shaped wet body is not particularly limited, and examples thereof include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. These may be used alone or in combination. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred because they can suppress the occurrence of cracks during drying.

[0175] (iii) Press Molding When producing a zirconia molded body by a method including a step of press-molding a powder containing zirconia-based particles, the specific press molding method is not particularly limited, and can be performed using a known press molding machine. Specific press molding methods include, for example, uniaxial pressing. The press pressure in press molding is appropriately set to an optimum value depending on the size, open porosity, biaxial bending strength, and particle size of the target molded body, and is usually 5 MPa to 1000 MPa. By increasing the press pressure during molding in the above production method, the pores of the resulting molded body are more fully filled, allowing the open porosity to be set lower and the density of the molded body to be increased. Furthermore, to increase the density of the resulting zirconia molded body, cold isostatic pressing (CIP) treatment may be further performed after uniaxial pressing.

[0176] The powder containing the zirconia-based particles used in press molding may further contain one or more of the above-mentioned other components such as binders, plasticizers, dispersants, emulsifiers, antifoaming agents, pH adjusters, lubricants, and light-transmittance adjusters. These components may be blended when preparing the powder.

[0177] (iv) Molding of a Resin-Containing Composition When a zirconia molded body is produced by a method including a step of molding a composition containing zirconia-based particles and a resin, the specific method for molding the composition is not particularly limited, and for example, injection molding, cast molding, extrusion molding, etc. may be used. Alternatively, a method of molding the composition by fusion dynamic molding (FDM), an inkjet method, a powder / binder lamination method, or other additive manufacturing methods (e.g., 3D printing) may also be used. Among these molding methods, injection molding and cast molding are preferred, and injection molding is more preferred.

[0178] The type of the resin is not particularly limited, and one that functions as a binder can be preferably used. Specific examples of the resin include paraffin wax, polyvinyl alcohol, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, atactic polypropylene, methacrylic resin, and fatty acids such as stearic acid. These resins may be used alone or in combination of two or more.

[0179] The composition containing the zirconia-based particles and resin may further contain one or more of the other components, such as the plasticizer, dispersant, emulsifier, antifoaming agent, pH adjuster, and lubricant, as described above.

[0180] (v) Polymerization of a composition containing a polymerizable monomer or oligomer. Polymerizing a composition containing zirconia-based particles and a polymerizable monomer or oligomer polymerizes the polymerizable monomer in the composition, thereby hardening the composition. When producing a zirconia molded body using a method including this polymerization step, the specific method is not particularly limited. For example, (a) a method of polymerizing a composition containing zirconia-based particles and a polymerizable monomer or oligomer in a mold; or (b) a stereolithography (SLA) method using a composition containing zirconia-based particles and a polymerizable monomer or oligomer can be employed. Among these, the stereolithography method (b) is preferred. The stereolithography method allows the zirconia molded body to be given a shape corresponding to the desired shape of the final zirconia sintered body at the time of production. Therefore, the stereolithography method may be particularly suitable when the zirconia sintered body of the present invention is used as a dental material for dental prostheses, etc.

[0181] The type of polymerizable monomer in the composition containing the zirconia-based particles and the polymerizable monomer or oligomer is not particularly limited, and may be any of monofunctional polymerizable monomers such as monofunctional (meth)acrylates and monofunctional (meth)acrylamides, and polyfunctional polymerizable monomers such as bifunctional aromatic compounds, bifunctional aliphatic compounds, and trifunctional or higher compounds. One type of polymerizable monomer may be used alone, or two or more types may be used. The oligomer is not particularly limited, as long as it is a compound in which two or more of the polymerizable monomers are bonded and has polymerizability. Among these, it is preferable to use a polyfunctional polymerizable monomer, especially when a stereolithography method is employed.

[0182] Examples of monofunctional (meth)acrylates include (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and sec-butyl (meth)acrylate. alkyl (meth)acrylates such as acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate; alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic group-containing (meth)acrylates such as benzyl (meth)acrylate and phenyl (meth)acrylate; and (meth)acrylates having a functional group such as 2,3-dibromopropyl (meth)acrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, and 11-(meth)acryloyloxyundecyltrimethoxysilane.

[0183] 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.

[0184] Among these monofunctional polymerizable monomers, (meth)acrylamide is preferred because of its excellent polymerizability, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.

[0185] Examples of bifunctional aromatic compounds include 2,2-bis((meth)acryloyloxyphenyl)propane, 2,2-bis[4-(2-hydroxy-3-acryloyloxypropoxy)phenyl]propane, 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (commonly known as "Bis-GMA"), 2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane, 2,2-bis (Meth)acrylates such as (4-(meth)acryloyloxydipropoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, and 1,4-bis(2-(meth)acryloyloxyethyl)pyromellitate are mentioned. Among these, Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article. Of the 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propanes, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average number of moles of ethoxy groups added: 2.6, commonly known as "D-2.6E") is preferred.

[0186] Examples of the bifunctional aliphatic compounds include glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of (meth)acrylates include triethylene glycol dimethacrylate (commonly known as "TEGDMA") and 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate (commonly known as "UDMA"), and other (meth)acrylates. Among these, triethylene glycol dimethacrylate (commonly known as "TEGDMA") and 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0187] Examples of tri- or higher functional compounds include (meth)acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacryloyloxy-2,2,6,6-tetra(meth)acryloyloxymethyl-4-oxaheptane. Among these, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetramethacrylate and 1,7-diacryloyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxaheptane are preferred in terms of excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0188] In both of the above methods (a) and (b), the polymerization of the composition is preferably carried out using a polymerization initiator, and the composition preferably further contains a polymerization initiator. There are no particular limitations on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred. Specific examples of photopolymerization initiators are the same as those described above in the explanation of gel casting, and a duplicated explanation will be omitted here.

[0189] The composition containing the zirconia-based particles and the polymerizable monomer may further contain one or more of the above-mentioned other components, such as a plasticizer, a dispersant, an emulsifier, an antifoaming agent, a pH adjuster, and a lubricant.

[0190] When a zirconia molded body is produced by stereolithography using a composition containing zirconia-based particles and a polymerizable monomer, the specific method of stereolithography is not particularly limited, and any known method can be appropriately employed for stereolithography. For example, a method can be employed in which a liquid composition is photopolymerized using an optical lithography device with ultraviolet light, a laser, or the like to sequentially form layers having the desired shape, thereby obtaining the desired zirconia molded body.

[0191] When obtaining a zirconia molded body by stereolithography, the content of zirconia-based particles in a composition containing zirconia-based particles and a polymerizable monomer is preferably as high as possible from the viewpoint of subsequent sintering properties. Specifically, the content of zirconia particles in the composition is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. On the other hand, in stereolithography, due to the principle of layered molding, it is preferable that the viscosity of the composition be within a certain range. Therefore, the content of zirconia-based particles in the composition is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less. Adjusting the viscosity of the composition can be particularly important when a controlled liquid level method is carried out in which a zirconia molded body is formed one layer at a time by curing layers by irradiating light from below a container through the bottom surface of the container, in order to raise the cured layer by one layer and allow the composition for forming the next layer to smoothly flow between the underside of the cured layer and the bottom surface of the container.

[0192] The specific viscosity of the composition at 25°C is preferably 20,000 mPa·s or less, more preferably 10,000 mPa·s or less, and even more preferably 5,000 mPa·s or less. Furthermore, the viscosity is preferably 100 mPa·s or more. Since the viscosity of the composition tends to increase as the zirconia particle content increases, it is preferable to appropriately adjust the balance between the zirconia particle content and viscosity of the composition in accordance with the performance of the stereolithography device used, taking into account the balance between the stereolithography speed and the precision of the resulting zirconia molded body. The viscosity can be measured using an E-type viscometer.

[0193] In the method for producing a zirconia molded body of the present invention, the zirconia molded body may be subjected to a humidification treatment followed by a CIP treatment in order to further improve the density of the zirconia molded body. When press molding is performed, a powder containing zirconia particles may be subjected to a humidification treatment before press molding, followed by press molding. The humidification method may be any known method without any limitations, and may involve spraying water with a spray bottle or using a hygrostat or thermo-hygrostat. The moisture content increase due to the humidification treatment depends on the particle size of the zirconia particles contained, the particle size of the stabilizer particles, etc., but is preferably greater than 2% by mass, more preferably greater than 3% by mass, even more preferably greater than 4% by mass, and particularly preferably greater than 5% by mass, relative to the mass of the powder before humidification treatment and the molded body. It is also preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 11% by mass or less. The moisture content of the powder after humidification can be calculated as a percentage by subtracting the mass of the powder before humidification and the compact from the mass of the wet powder (powder after humidification) and the compact, and dividing the result by the mass of the powder before humidification and the compact. The pressure for the CIP treatment is the same as that described above in the description of press molding.

[0194] (vi) Step of additive manufacturing of granules containing zirconia-based particles When manufacturing granules containing zirconia-based particles, there are no particular limitations on the specific method. For example, a method can be used in which a slurry is obtained and then dried in a spray dryer to form granules, and the resulting granules can be used for powder additive manufacturing. There are no particular limitations on the powder additive manufacturing method, but examples include a powder bed method, an SLS method (selective laser sintering method), an SLM method (selective laser melting method), an electron beam method, an arc discharge method, and a binder jet method. For methods in which it is preferable to not use organic substances during additive manufacturing, it is preferable not to use organic substances even in the granule manufacturing stage.

[0195] [Zirconia Sintered Body] Next, the zirconia sintered body of the present invention will be described. The zirconia sintered body of the present invention can be produced using a zirconia calcined body. Specifically, the zirconia sintered body of the present invention can be obtained, for example, by sintering the above-mentioned zirconia calcined body. The zirconia sintered body is in a completely sintered state in which zirconia particles are solidified by sintering, the relative density increases as sintering proceeds, and densification progresses, with the relative density being 95% or more.

[0196] The content of the stabilizer in the zirconia sintered body of the present invention is the same as the content of the stabilizer in the zirconia calcined body.

[0197] The zirconia sintered body of the present invention satisfies the above formula (1) when the first translucency ΔL1 *(W-B) of a zirconia sintered body produced by sintering at 1550° C. for 120 minutes is compared with the second translucency ΔL2 *(W-B) of a zirconia sintered body produced by sintering at 1550° C. for 10 minutes. Therefore, the zirconia sintered body of the present invention can maintain high translucency equivalent to that of long-term sintering after sintering for a short time, in which the holding time at the maximum sintering temperature is 10 minutes or less.

[0198] The zirconia sintered body of the present invention may contain a fluorescent agent. The fluorescent agent is the same as the fluorescent agent in the zirconia calcined body. The zirconia sintered body of the present invention may contain one type of fluorescent agent alone or two or more types in combination. In this specification, regarding the fluorescent agent, "relative to 100% by mass of zirconia contained in the zirconia calcined body" can be read as "relative to 100% by mass of zirconia contained in the zirconia sintered body."

[0199] The zirconia sintered body of the present invention may contain a colorant. Examples of the colorant include the same colorants as those used in the zirconia calcined body.

[0200] The content of the colorant in the zirconia sintered body is not particularly limited and can be adjusted appropriately depending on the type of colorant and the application of the zirconia sintered body, but from the viewpoint of favorable use as a dental prosthesis, the content of the colorant, calculated as the oxide of the metal element contained in the colorant, relative to 100% by mass of zirconia contained in the zirconia sintered body, is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more. Furthermore, the content of the colorant, calculated as the oxide of the metal element contained in the colorant, is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and may be 0.1% by mass or less, or even 0.05% by mass or less.

[0201] In order to adjust the translucency of the zirconia sintered body of the present invention, the zirconia sintered body of the present invention may contain a translucency adjuster. Examples of the translucency adjuster include the same ones as those used in the zirconia calcined body.

[0202] The content of the light-transmitting adjuster in the zirconia sintered body is not particularly limited, and can be appropriately adjusted depending on the type of light-transmitting adjuster and the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the content is preferably 0.1% by mass or less relative to 100% by mass of zirconia contained in the zirconia sintered body.

[0203] [Method of Manufacturing Zirconia Sintered Body] Examples of methods for manufacturing the zirconia sintered body of the present invention include methods for manufacturing a zirconia sintered body by sintering the above-mentioned zirconia calcined body. A manufacturing method including a step of sintering the above-mentioned zirconia calcined body under normal pressure at a temperature higher than 900°C and not higher than 1700°C is preferred. By using such a manufacturing method, it is possible to easily manufacture the zirconia sintered body of the present invention, which can maintain high translucency equivalent to that achieved by long-term sintering after sintering for a short period of time, i.e., a holding time of 10 minutes or less at the maximum sintering temperature.

[0204] The zirconia sintered body of the present invention can also be produced by sintering the zirconia calcined body of the present invention under normal pressure.

[0205] When producing a sintered body by sintering the zirconia calcined body of the present invention, the sinterable temperature (e.g., the maximum sintering temperature) is preferably set at a temperature that maximizes the translucency of the zirconia sintered body. From the viewpoint of easily obtaining the desired zirconia sintered body under normal pressure, the sinterable temperature is preferably above 900°C, more preferably above 1000°C, and even more preferably above 1050°C. It is also preferably below 1700°C, more preferably below 1650°C, and even more preferably below 1600°C. In a preferred embodiment, a method for producing a zirconia sintered body includes sintering a zirconia calcined body at above 900°C and below 1560°C under normal pressure, because excellent translucency is achieved even in a short sintering time, even at a lower sinterable temperature. Compared to conventional techniques, this method is industrially advantageous because it provides excellent translucency even in a short sintering time at a lower sinterable temperature. By setting the sinterable temperature at or above the lower limit and below the upper limit, sintering can be carried out sufficiently, and a dense sintered body can be easily obtained. Furthermore, by ensuring that the sinterable temperature is equal to or lower than the upper limit, it is possible to prevent the fluorescent agent from being deactivated.

[0206] When producing a sintered body, there is no particular limitation on the sintering time as long as the holding time at the maximum sintering temperature is 10 minutes or less, but because the desired zirconia sintered body can be obtained efficiently and stably with good productivity, the holding time at a sinterable temperature (for example, the maximum sintering temperature) is preferably 10 minutes or less, more preferably 9 minutes or less, even more preferably 8 minutes or less, even more preferably 7 minutes or less, particularly preferably 6 minutes or less, and most preferably 5 minutes or less. The holding time is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 3 minutes or more.

[0207] When producing a sintered body, the sintering time required to produce the sintered body can be shortened without reducing the translucency of the resulting zirconia sintered body. In particular, the holding time at the maximum sintering temperature required to produce the sintered body can be shortened to 10 minutes or less. This improves production efficiency, and when the zirconia calcined body of the present invention is used in a dental product, it shortens the time required from determining the dimensions of the dental product to be used in treatment and cutting it to making the dental product ready for treatment, thereby reducing the time burden on patients. It also reduces energy costs.

[0208] The temperature increase rate and temperature decrease rate in the sintering step are preferably set so as to shorten the time required for the sintering step. For example, the temperature increase rate can be set so as to reach the maximum sintering temperature in the shortest time depending on the performance of the sintering furnace. The temperature increase rate to the maximum sintering temperature can be, for example, 10°C / min or more, 50°C / min or more, 100°C / min or more, 120°C / min or more, 150°C / min or more, or 200°C / min or more. The temperature decrease rate is preferably set so as not to cause defects such as cracks in the sintered body. For example, after heating is completed, the sintered body can be allowed to cool at room temperature.

[0209] The sintering in the present invention can be carried out using a sintering furnace. There are no particular limitations on the type of sintering furnace, and for example, electric furnaces and degreasing furnaces used in general industry can be used. In particular, when used for dental materials, in addition to conventional sintering furnaces for dental zirconia, dental porcelain furnaces with relatively low sintering temperatures (e.g., maximum sintering temperatures) can also be used.

[0210] The zirconia sintered body of the present invention can be easily produced without HIP treatment, but by performing HIP treatment after the above-mentioned sintering under normal pressure, it is possible to further improve the translucency and mechanical strength.

[0211] [Uses of Zirconia Sintered Body] There are no particular limitations on the uses of the zirconia sintered body of the present invention. The zirconia sintered body of the present invention has excellent translucency and excellent in-line light transmittance, making it particularly suitable as a dental material for dental prostheses and the like. In particular, it is extremely useful not only as a dental prosthesis used in the cervical region of teeth, but also as a dental prosthesis used on the occlusal surfaces of molars and the incisal edges of front teeth. The zirconia sintered body of the present invention is extremely useful, particularly as a dental prosthesis used in the incisal edges of front teeth.

[0212] The present invention includes embodiments in which the above-described configurations are combined in various ways within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved.

[0213] Next, the present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way, and many modifications within the technical scope of the present invention are possible by those skilled in the art.

[0214] [Raw material powders] Monoclinic 0Y: zirconia powder ("TZ-0" manufactured by Tosoh Corporation) Tetragonal 3Y: zirconia powder with 3 mol% yttria solid solution ("TZ-3Y-E" manufactured by Tosoh Corporation) Cubic 6Y: zirconia powder with 6 mol% yttria solid solution ("TZ-6Y" manufactured by Tosoh Corporation) Cubic 10Y: zirconia powder with 10 mol% yttria solid solution ("TZ-10Y" manufactured by Tosoh Corporation) Cubic 15Y: A hydrated zirconia sol obtained by hydrolyzing an aqueous zirconium oxychloride solution was mixed with yttria and dried, and the resulting powder was heat-treated in air at 1,160°C for 2 hours to obtain an yttria-containing zirconia powder with an yttria content of 15 mol%. Yttria: yttria powder (Y2O3 manufactured by Treibacher Industrie AG)

[0215] Examples 1 to 15 and Comparative Examples 1 to 6 Preparation of Zirconia Compositions of Examples 1 to 15 and Comparative Examples 1 to 3 To prepare the granular raw material compositions of each Example and Comparative Example, the raw material powders described above were mixed to have the compositions shown in Table 1, water was added, and the mixture was wet-pulverized and mixed in a ball mill for 20 hours. A binder was added to the pulverized slurry, and the mixture was dried in a spray dryer to obtain granular zirconia compositions. In Tables 1 and 2 below, the "total yttria content" represents the yttria content relative to the total moles of zirconia and yttria.

[0216] [Preparation of zirconia compositions of comparative examples 4 and 5] The above raw material powders were mixed to the compositions shown in Table 1, water was added, and the mixture was wet-pulverized and mixed in a ball mill for 20 hours. A binder was added to the pulverized slurry, and the mixture was dried in a spray dryer to obtain granules. The granules were heated to 1000°C at a rate of 10°C / min and held for 2 hours. Water was then added, and the mixture was wet-pulverized and mixed in a ball mill for 20 hours. A binder was added to the pulverized slurry, and the mixture was dried in a spray dryer to obtain a granular zirconia composition.

[0217] [Preparation of Zirconia Composition of Comparative Example 6] The monoclinic 0Y powder and tetragonal 3Y powder were mixed to obtain the composition shown in Table 1, and water was added thereto, followed by wet-pulverization and mixing in a ball mill for 15 hours to obtain a slurry. Yttria powder was mixed with this slurry to obtain the composition shown in Table 1, and water was added thereto, followed by wet-pulverization and mixing in a ball mill for an additional 5 hours. A binder was added to the pulverized slurry, and the mixture was then dried in a spray dryer to obtain a granular zirconia composition.

[0218] [Preparation of Zirconia Calcined Body] For each of the Examples and Comparative Examples, a pellet-shaped calcined body was prepared as follows to obtain a zirconia sintered body sample for translucency evaluation. First, a cylindrical mold having a diameter of 19 mm was used, and the raw material composition was placed in the mold so that the thickness of the workable zirconia composite sintered body after sintering would be 1.2 mm. Next, the raw material composition was press-molded using a uniaxial press molding machine at a surface pressure of 200 MPa to prepare a pellet-shaped compact. The obtained pellet-shaped compact was heated to 1000°C at a rate of 10°C / min using a firing furnace "Noritake Katana (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd., and then cooled to obtain a zirconia calcined body.

[0219] [Preparation of zirconia sintered body] The obtained pellet-shaped calcined body was sintered at 1550°C for 120 minutes using a sintering furnace "Noritake Katana (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd. to prepare a sample for measuring ΔL1*(W-B) of the first sintered body, and a sample for measuring ΔL2*(W-B) of the second sintered body was prepared by sintering at 1550°C for 10 minutes.

[0220] The properties of the zirconia sintered bodies produced in each of the Examples and Comparative Examples were measured by the following methods.

[0221] <Method for Measuring the Average Primary Particle Diameter of Particles in a Zirconia Composition> The average primary particle diameter of each particle (zirconia particles, yttria particles) in the zirconia composition was measured by the following method for the primary particles constituting the granules obtained by the above-described method for producing a zirconia composition using each raw material powder alone. Surface images (SEM images) of the obtained granular powder were obtained using a scanning electron microscope (product name "VE-9800", manufactured by Keyence Corporation). The grain boundaries of each particle were noted on the obtained images, and the average primary particle diameter was calculated by image analysis. Image analysis software (product name "Image-Pro Plus ver. 7.0.1", manufactured by Hakuto Co., Ltd.) was used to measure the particle diameter. The captured SEM images were binarized, and the brightness range was adjusted so that the grain boundaries were clearly visible, allowing the particles to be recognized from the field of view (area). The particle diameter obtained using Image-Pro Plus is the diameter passing through the center of gravity of the particle. The diameter passing through the center of gravity of the particle is calculated by measuring the length of the line segment connecting the outlines passing through the center of gravity, determined from the outline of the particle, at intervals of 2 degrees from the center of gravity, and averaging the measured values ​​(180 pieces). In measuring particle diameter, particles not on the edge of the image were measured. "Particles not on the edge of the image" refers to particles excluding particles whose outlines do not fit completely within the screen of the SEM photograph (particles whose outlines are interrupted at the top, bottom, left, and right boundary lines). The particle diameters of all particles not on the edge of the image were determined by selecting the option to exclude particles on all boundary lines in Image-Pro Plus. The particle diameters of each granule in three fields of view were obtained for one sample in each Example and Comparative Example, and the average primary particle diameter was calculated.

[0222] <Content (mol %) of Stabilizer in Zirconia Composition and Zirconia Calcined Body> The content (mol %) of the stabilizer in the zirconia composition and the zirconia calcined body was measured as the content of the stabilizer relative to the total moles of zirconia and the stabilizer using an X-ray fluorescence analysis (XRF) device (RX3000, manufactured by Matsusada Precision Co., Ltd.).

[0223] <Evaluation of Crystalline Phase Ratio of Zirconia Calcined Body> The tetragonal phase ratio f of the zirconia calcined body t , cubic crystal fraction f c, and monoclinic fraction f m was determined by analyzing the crystalline phase in the zirconia calcined body. Specifically, as X-ray diffraction measurement, a fully automatic horizontal multipurpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and X-ray analysis integrated software (SmartLab Studio II, manufactured by Rigaku Corporation) were used to measure under the following conditions, and the area intensity of each peak (peak area intensity I) was determined. X-ray source: Cu Kα (λ = 1.54186 Å) Goniometer length: 300 mm Optical system: focusing method Detector: high-speed one-dimensional X-ray detector (D / teX Ultra 250) Monochromatization: Kβ filter Tube voltage: 40 kV Tube current: 30 mA Scan axis: 2θ / θ Scan speed: 0.2 ° / min Sampling step: 0.01 °

[0224] The crystalline phase ratio was calculated from the following formulas (2-1), (2-2), and (2-3) by assigning each peak to a crystalline phase. t (%) = I t / (I m +I t +I c +I y )×100 (2-1) Cubic crystal ratio f c (%) = I c / (I m +I t +I c +I y ) × 100 (2-2) Monoclinic crystal ratio f m (%) = I m / (I m +I t +I c +I y )×100 (2-3) (where f m is the monoclinic crystal ratio (%), f t is the tetragonal crystal ratio (%), f c represents the cubic crystal ratio (%), and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.2° where the peak top of the main peak of the tetragonal system appears, and I crepresents the area intensity of the peak at 2θ=30.1° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2° where the peak top of the main peak of undissolved yttria appears.) For the measurements, disk-shaped calcined zirconia bodies of each example and comparative example were used as samples.

[0225] <Measurement of the Proportion of Yttria Not Solubilized in Zirconia of Zirconia Calcined Body> The content f of undissolved yttria in the zirconia calcined body was y was measured by X-ray diffraction (XRD) using CuKα radiation and calculated from the following formula (2-4): y (%) = I y / (I m +I t +I c +I y )×100 (2-4) (where f y represents the proportion (%) of undissolved yttria, and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.2° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak at 2θ=30.1° where the peak top of the main peak of the cubic crystal system appears, and I y represents the integrated intensity of the peak near 2θ=29.2° where the peak top of the main peak of undissolved yttria appears.)

[0226] <Measurement of Standard Deviation of Yttrium Element Distribution in Zirconia Calcined Body> The yttrium element distribution in the zirconia calcined body was measured using a field emission scanning electron microscope (FE-SEM Reglus 8220, manufactured by Hitachi High-Tech Corporation) and an energy dispersive X-ray analyzer (Aztec Energy X-Max 50, manufactured by Oxford Instruments) under the following conditions, and the yttrium element was observed at 1.923 keV. The standard deviation (mol%) of the yttrium element for 10 particles derived from the stabilizer was determined. Measurement magnification: 20,000x Analysis mode: Point analysis Acceleration voltage: 5 kV Working distance: 15 mm±1 mm X-ray take-off angle: 30 degrees Dead time: 7% Measurement time: 100 seconds

[0227] <Method for measuring the average primary particle size of particles in a zirconia calcined body> For the zirconia calcined bodies obtained in the examples or comparative examples, an image (SEM image) of the surface was obtained using a scanning electron microscope (product name "VE-9800", manufactured by Keyence Corporation). The grain boundaries of each crystal particle were noted on the obtained image, and then the primary particle size of each crystal particle was measured by image analysis. For particle size measurement, image analysis software (product name "Image-Pro Plus ver. 7.0.1", manufactured by Hakuto Co., Ltd.) was used to binarize the captured SEM image, adjust the brightness range so that the grain boundaries were clearly visible, and recognize the particles from the field of view (area). The particle diameter obtained using Image-Pro Plus is the diameter passing through the center of gravity of the particle. The diameter passing through the center of gravity of the particle is the average of the values ​​(180) measured by measuring the length of the line segment connecting the outlines passing through the center of gravity determined from the outline of the particle at intervals of 2 degrees from the center of gravity. In measuring particle diameter, particles not on the edge of the image were measured. "Particles not on the edge of the image" refers to particles excluding particles whose outlines do not fit completely within the screen of the SEM photograph (particles whose outlines are interrupted at the top, bottom, left, and right boundary lines). The particle diameters of all particles not on the edge of the image were determined by selecting the option to exclude particles on all boundary lines in Image-Pro Plus. The particle diameters of each crystal particle in three fields of view were obtained for one sample of each example and comparative example, and the average primary particle diameter was calculated.

[0228] <Evaluation of Translucency of Zirconia Sintered Body (Measurement of ΔL*(W-B))> The calcined bodies obtained in the Examples and Comparative Examples were fired at a maximum sintering temperature of 1550°C and a holding time at the maximum sintering temperature of 120 minutes (120-minute sintering), to produce zirconia sintered bodies (first sintered bodies). Next, the calcined bodies produced by the same method were fired at a maximum sintering temperature of 1550°C and a holding time at the maximum sintering temperature of 10 minutes (10-minute sintering), to produce zirconia sintered bodies (second sintered bodies). The heating rate and cooling rate were set to the same for the 10-minute sintering and the 120-minute sintering. The two types of zirconia sintered bodies obtained were each polished into a flat plate sample with a thickness of 1.20 mm, which was used as a sample for measuring translucency. The translucency of the samples was measured using a spectrophotometer (product name "Crystal Eye") manufactured by Olympus Corporation, using a 7-band LED light source as the measurement mode. Specifically, the lightness (LW*) of a zirconia sintered body, which is a flat sample, measured against a white background, and the lightness (LB*) of the same sample measured against a black background using the same measuring device, measuring mode, and light source were measured to determine the light transmittance (ΔL*(W-B)) as the difference between the two (ΔL*=(LW*)-(LB*)) (average value of n=3). The L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013). The first translucency ΔL1*(W-B) of the first sintered body produced by sintering at 1550°C for 120 minutes and the second translucency ΔL2*(W-B) of the second sintered body produced by sintering at 1550°C for 10 minutes were determined, and the ratio of ΔL2*(W-B) to ΔL1*(W-B) (ΔL2*(W-B) / ΔL1*(W-B)) was calculated as the rate of change in translucency. A rate of change in translucency of 0.85 or more (85% or more) was considered acceptable.

[0229] The evaluation results of the zirconia calcined body and the zirconia sintered body are shown in Table 2.

[0230]

[0231] As shown in Table 2, in Comparative Examples 1 to 6, the translucency was lower in the short-time sintering with a holding time of 10 minutes at the maximum sintering temperature than in the sintering with a holding time of 2 hours at the maximum sintering temperature. In contrast, in Examples 1 to 15, the translucency was comparable to that of the sintering with a holding time of 2 hours at the maximum sintering temperature, even in the short-time sintering with a holding time of 10 minutes at the maximum sintering temperature.

[0232] The zirconia calcined body and composition of the present invention, as well as the method for producing the same, are useful as dental materials such as dental prostheses.

Claims

1. A partially sintered zirconia green body in which zirconia particles are consolidated to such an extent that they do not reach sintering, ΔL related to the first sintered body containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, and obtained by sintering the zirconia green compact at 1550 °C for 120 minutes 1 * (W - B) and ΔL related to the second sintered body obtained by sintering at 1550 °C for 10 minutes 2 * A zirconia green compact that satisfies the following formula (1) when compared with (W - B). ΔL 2 *(W - B) / ΔL 1 *(W - B) ≥ 0.85 (1)

2. The partially sintered zirconia green body according to Claim 1, satisfying any one of the following conditions (i) or (ii). (i) The zirconia contains tetragonal zirconia, and a part of the stabilizer is a stabilizer that is not dissolved in the zirconia; or (ii) The zirconia contains monoclinic zirconia and cubic zirconia.

3. The stabilizer is yttria (Y 2 O 3 ), the zirconia calcined body according to claim 1 or 2.

4. The partially sintered zirconia green body according to Claim 3, satisfying any one of the following conditions (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6). (A-1) The zirconia contains monoclinic zirconia and tetragonal zirconia, the content rate of the monoclinic phase is 55% or more, the content rate of the tetragonal phase is 10% or more, and a part of the yttria is yttria that is not dissolved in the zirconia; (A-2) The zirconia contains tetragonal zirconia, does not fall under (A-1), the content rate of the tetragonal phase is 10% or more, and a part of the yttria is yttria that is not dissolved in the zirconia; (A-3) The zirconia contains monoclinic zirconia and cubic zirconia, the content rate of the monoclinic phase is 55% or more, and the content rate of the cubic phase is 15% or more; (A-4) The zirconia contains monoclinic zirconia and cubic zirconia, does not fall under (A-3), and the content rate of the cubic phase is 15% or more; (A-5) The zirconia contains tetragonal zirconia and cubic zirconia, the content rate of the tetragonal phase is 5% or more and less than 50%, the content rate of the cubic phase is 50% or more and less than 95%, and a part of the yttria is yttria that is not dissolved in the zirconia; (A-6) The zirconia contains tetragonal zirconia and cubic zirconia, does not fall under (A-5), the content rate of the cubic phase is 10% or more and less than 50%, and a part of the yttria is yttria that is not dissolved in the zirconia. The content rates of the tetragonal phase, cubic phase, and monoclinic phase in (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6) are calculated from the following formulas, respectively. Cubic ratio f t (%) = I t / (I m + I t + I c + I y ) × 100 (2 - 1) Cubic crystal ratio f c (%) = I c / (I m + I t + I c + I y ) × 100 (2 - 2) Monoclinic ratio f m (%) = I m / (I m + I t + I c + I y ) × 100 (2 - 3) (where f m represents the monoclinic ratio (%), f t represents the tetragonal ratio (%), f c represents the cubic ratio (%). In XRD measurement, I m represents the peak area intensity of the peak near 2θ = 28.2° where the peak top of the main peak of the monoclinic system appears. I t represents the peak area intensity of the peak near 2θ = 30.2° where the peak top of the main peak of the tetragonal system appears. I c represents the peak area intensity of the peak near 2θ = 30.1° where the peak top of the main peak of the cubic system appears. I y represents the peak area intensity of the peak near 2θ = 29.2° where the peak top of the main peak of un-dissolved yttria appears.)

5. The zirconia calcined body according to claim 3, wherein the standard deviation of the yttrium element distribution is 2 mol% or more and less than 21 mol%.

6. The zirconia calcined body according to claim 4, which satisfies the condition (A-1) or (A-2), and the proportion of yttria not dissolved in zirconia is 1 to 25%.

7. The zirconia calcined body according to claim 4, which satisfies the condition (A-3) or (A-4), and a part of the yttria is yttria not dissolved in zirconia, and the proportion of yttria not dissolved in zirconia is 1 to 15%.

8. The zirconia calcined body according to claim 1 or 2, wherein the content of the stabilizer is 2 to 9 mol% based on the total mol of zirconia and the stabilizer.

9. The density is 3.6 g / cm 3 The zirconia calcined body according to claim 1 or 2, wherein the density is 3.6 g / cm or less.

10. The zirconia calcined body according to claim 1 or 2, wherein the average primary particle size is 40 to 110 nm.

11. A zirconia composition containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, ΔL related to the first sintered body produced by sintering the zirconia composition at 1550 °C for 120 minutes 1 *(W - B) and ΔL related to the second sintered body produced by sintering at 1550 °C for 10 minutes 2 *(W - B), a zirconia composition that satisfies the following formula (1) when compared ΔL 2 *(W - B) / ΔL 1 *(W - B) ≥ 0.85 (1)

12. The zirconia composition according to claim 11, which satisfies any one of the following conditions (i) or (ii). (i) It contains zirconia powder (T) in which the zirconia is tetragonal, and a part of the stabilizer is stabilizer powder not dissolved in zirconia; or (ii) It contains zirconia powder (M) in which the zirconia is monoclinic and zirconia powder (C) in which the zirconia is cubic.

13. The zirconia composition according to claim 12, which satisfies the condition (i) and further contains zirconia powder (M) in which the zirconia is monoclinic.

14. The zirconia composition according to claim 13, wherein the ratio of the total mass of the zirconia powder (T) and the zirconia powder (M) to the mass of the stabilizer powder is 85.0% by mass: 15.0% by mass to 99.8% by mass: 0.2% by mass.

15. The zirconia composition according to claim 13 or 14, wherein the zirconia powder (M) is 0 to 85% by mass in the total mass of the zirconia powder (T) and the zirconia powder (M).

16. The zirconia composition according to claim 12 or 13, wherein the zirconia powder (T) contains a stabilizer capable of suppressing the phase transition of the dissolved zirconia, and the content of the dissolved stabilizer is 2 to 4 mol% based on the total mol of zirconia and the stabilizer.

17. The zirconia composition according to claim 12, which satisfies the condition (ii), and in which part of the stabilizer is a stabilizer that is not dissolved in zirconia.

18. The zirconia composition according to claim 12 or 17, wherein the ratio of the total mass of the zirconia powder (M) and the zirconia powder (C) to the mass of the stabilizer powder is 85.0% by mass: 15.0% by mass to 100% by mass: 0% by mass.

19. The zirconia composition according to claim 12 or 17, wherein the zirconia powder (C) is 15.0 to 95.0% by mass in the total mass of the zirconia powder (M) and the zirconia powder (C).

20. The zirconia composition according to claim 12 or 17, wherein the content of the stabilizer in the zirconia powder (M) is 0 to 1 mol% with respect to the total mol of the zirconia powder (M) and the stabilizer.

21. The zirconia composition according to claim 12 or 17, wherein the zirconia powder (C) contains a stabilizer capable of suppressing the phase transition of the dissolved zirconia, and the content of the dissolved stabilizer is 5 mol% or more and 15 mol% or less with respect to the total mol of the zirconia powder (C) and the stabilizer.

22. The zirconia composition according to claim 12, which satisfies the condition (i), further contains a zirconia powder (T) having a cubic crystal system, and the ratio of the total mass of the zirconia powder (T) and the zirconia powder (C) to the mass of the stabilizer powder is 88.0% by mass: 12.0% by mass to 99.999% by mass: 0.001% by mass.

23. The zirconia composition according to claim 11 or 12, wherein the average primary particle diameter (r1) of the zirconia powder (T), the zirconia powder (C), and the zirconia powder (M) is 40 to 110 nm.

24. A method for producing a zirconia green compact, which comprises firing the zirconia composition according to claim 11 or 12 to such an extent that the zirconia particles do not sinter together.

25. A method for producing a zirconia sintered body, which comprises sintering the zirconia green compact according to claim 1 or 2.