Zirconium oxide presintered body and composition, and method for producing same

Abstract

Provided are: a pre-sintered body for obtaining a zirconia sintered body capable of maintaining high light transmittance as high as long-term sintering after short-term sintering in which the holding time at the maximum sintering temperature is 10 minutes or less; a composition; and methods for producing the pre-sintered body and the composition. The present invention relates to a zirconia pre-sintered body in which zirconia particles are consolidated to each other so as not to be sintered, the zirconia pre-sintered body containing a stabilizing agent capable of suppressing the phase change of zirconia, when [Delta] L1 * (W-B) of a first sintered body produced by sintering at 1550 DEG C for 120 minutes is compared with [Delta] L2 * (W-B) of a second sintered body produced by sintering at 1550 DEG C for 10 minutes, formula (1) is satisfied. [Delta] L2 * (W-B) / [Delta] L1 * (W-B) > = 0.85 (1).

Description

Technical Field

[0001] The present invention relates to a zirconia pre-sintered body, a composition, and a method for manufacturing the same. More specifically, the present invention relates to a zirconia (zirconium(IV); ZrO 2 ) pre-sintered body and a composition having high translucency even when sintered for a short time, and a method for manufacturing the same. Background Art

[0002] Oxide ceramics are widely used industrially. Among them, yttria-containing zirconia sintered bodies have been used in recent years for dental materials such as dental prostheses due to their high strength and aesthetic properties. As raw materials for such zirconia sintered bodies, zirconia powder and yttria powder are mainly used separately, or a substance in which they are solid-solved is often used. After obtaining a pre-sintered body (grinding blank) by pulverizing and mixing such raw materials, drying, molding, and heat treatment, the pre-sintered body is machined into a shape similar to that of a target dental prosthesis, and then sintered further to manufacture dental materials such as dental prostheses.

[0003] In the sintering of dental prostheses, it is important that the treatment time can be shortened to the extent that it can be completed in a short time, and that the aesthetic properties of the prostheses are constant even when sintered using various calcining furnaces with different output powers, that is, the translucency is constant regardless of whether the sintering time is short or long.

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

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

[0006] To solve such sintering problems in a short time, Patent Documents 2, 3, etc. have been proposed. Patent Document 2 discloses that by using zirconia and yttria as raw materials separately and simultaneously using a tetragonal crystal solid-solved with zirconia and yttria, the difference in translucency between a zirconia sintered body obtained by a short-time residence of 30 minutes at the maximum sintering temperature and a zirconia sintered body obtained by a long-time residence of about 2 hours is small, and excellent translucency at 15-minute sintering is disclosed.

[0007] Furthermore, in Patent Document 3, as a powder material for manufacturing a sintered body or a work piece to be cut, a dental cutting zirconia work piece with a porosity of 15 to 30% obtained using Zpex Smile (registered trademark) etc. is disclosed, and in a specific embodiment, a sintered body excellent in translucency and strength can be obtained by short-time sintering.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-52806

[0011] Patent Document 2: International Publication No. 2018 / 056330

[0012] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2020-033338 Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] On the other hand, the shorter the sintering time, the more advantageous it is from the aspect of manufacturing cost. The inventors confirmed in their research that: in order to further shorten the sintering time and further shorten the holding time at the maximum sintering temperature from about 30 minutes, for example, in a short residence time of 10 minutes, in the invention described in Patent Document 1, since the concentrations of zirconium element and yttrium element do not have a sufficient gradient to utilize the mass transfer between the tetragonal phase and cubic phase crystals to promote sintering, there is a problem that the translucency is lower compared to a long residence time of about 2 hours.

[0015] In addition, in Patent Document 2, when the holding time at the maximum sintering temperature is shortened to 10 minutes, there is the following problem: the residual rate of the monoclinic phase that does not undergo a phase change and remains in the pre-sintered body is high, and the reaction rate is insufficient to change from the monoclinic phase to the tetragonal phase or cubic phase. When the holding time at the maximum sintering temperature is a short residence time of about 10 minutes compared to a long residence time of about 2 hours, the translucency is low.

[0016] Furthermore, Patent Document 3 does not describe the use of yttrium oxide not dissolved in zirconia in short-time sintering with a holding time of 2 minutes at the maximum sintering temperature, and only discloses a zirconia work piece made of yttrium dissolved in zirconia. Reference Example 1 discloses that sufficient translucency cannot be obtained unless yttrium dissolved in zirconia is used. In addition, it is not clearly described that even in short-time sintering, the translucency of the zirconia sintered body obtained by the short-time sintering with the holding time of 2 minutes is the same as that of the zirconia sintered body obtained by the sintering with the holding time of 2 hours.

[0017] In Patent Document 3, the reason why a yttrium compound that is not dissolved in zirconia cannot be sintered in a short time is that the yttrium compound that is not dissolved in zirconia is not a material that favorably promotes the diffusion of substances.

[0018] Therefore, when the zirconia green compact contains a yttrium compound that is not dissolved in zirconia, for example, there is a problem that the light transmittance of the zirconia sintered body obtained by short-term residence at a maximum sintering temperature for about 10 minutes is lower than that of the zirconia sintered body obtained by long-term residence for about 2 hours.

[0019] An object of the present invention is to provide a zirconia green compact, a composition, and a method for manufacturing the same, which are used to obtain a zirconia sintered body that can maintain a high light transmittance equivalent to that of long-term sintering after short-term sintering at a maximum sintering temperature for 10 minutes or less.

[0020] Means for Solving the Problem

[0021] The present inventors repeatedly conducted in-depth research to solve the above problems and found that: for a zirconia green compact (grinding blank), controlling the range of the average primary particle diameter of the particles constituting the raw material powder for manufacturing the green compact and the height of the concentration gradient of zirconium and yttrium elements between the respective crystals contained in the particles, that is, the range of the standard deviation of the yttrium element distribution in the microphase region, is useful for favorably promoting the diffusion of substances and obtaining a zirconia sintered body that can maintain a high light transmittance equivalent to that of long-term sintering after short-term sintering. Based on this insight, further research was conducted, and thus the present invention was completed.

[0022] That is, the present invention includes the following technical solutions.

[0023] [1] A zirconia green compact, which is a zirconia green compact in which zirconia particles are consolidated to such an extent that they do not reach sintering,

[0024] which contains zirconia and a stabilizer capable of suppressing the phase transformation of zirconia, and the ΔL 1 *(W - B) of the first sintered body produced by sintering the aforementioned zirconia green compact at 1550 °C for 120 minutes and the ΔL 2 *(W - B) of the second sintered body produced by sintering at 1550 °C for 10 minutes satisfy the following formula (1) when compared.

[0025] ΔL 2 *(W - B) / ΔL 1 *(W - B) ≥ 0.85 (1)

[0026] [2] The zirconia green compact according to [1], which satisfies any one of the following conditions (i) or (ii).

[0027] (i) The zirconia described above contains tetragonal zirconia, and a part of the stabilizer is a stabilizer that is not dissolved in the zirconia; or

[0028] (ii) The zirconia described above contains monoclinic zirconia and cubic zirconia.

[0029] [3] The pre-fired zirconia body according to [1] or [2], wherein the stabilizer is yttrium oxide (Y 2 O 3 ).

[0030] [4] The pre-fired zirconia body according to [3] satisfies any one of the following conditions (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6).

[0031] (A-1) The zirconia described above contains monoclinic zirconia and tetragonal zirconia, the content rate of the monoclinic system is 55% or more, the content rate of the tetragonal system is 10% or more, and a part of the yttrium oxide is yttrium oxide that is not dissolved in the zirconia;

[0032] (A-2) The zirconia described above contains tetragonal zirconia, does not conform to (A-1), the content rate of the tetragonal system is 10% or more, and a part of the yttrium oxide is yttrium oxide that is not dissolved in the zirconia;

[0033] (A-3) The zirconia described above contains monoclinic zirconia and cubic zirconia, the content rate of the monoclinic system is 55% or more, and the content rate of the cubic system is 15% or more;

[0034] (A-4) The zirconia described above contains monoclinic zirconia and cubic zirconia, does not conform to (A-3), and the content rate of the cubic system is 15% or more;

[0035] (A-5) The zirconia described above contains tetragonal zirconia and cubic zirconia, the content rate of the tetragonal system is 5% or more and less than 50%, the content rate of the cubic system is 50% or more and less than 95%, and a part of the yttrium oxide is yttrium oxide that is not dissolved in the zirconia;

[0036] (A-6) The zirconia described above contains tetragonal zirconia and cubic zirconia, does not conform to (A-5), the content rate of the cubic system is 10% or more and less than 50%, and a part of the yttrium oxide is yttrium oxide that is not dissolved in the zirconia.

[0037] The content ratios of tetragonal, cubic, and monoclinic systems in the foregoing (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6) are calculated according to the following formulas, respectively.

[0038] Tetragonal ratio f t (%) = I t / (I m + I t + I c + I y ) × 100 (2-1)

[0039] Cubic ratio f c (%) = I c / (I m + I t + I c + I y ) × 100 (2-2)

[0040] Monoclinic ratio f m (%) = I m / (I m + I t + I c + I y ) × 100 (2-3)

[0041] (In the formula, 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 near 2θ = 28.2° at the peak top of the main peak of the monoclinic system, I t represents the peak area intensity near 2θ = 30.2° at the peak top of the main peak of the tetragonal system, I c represents the peak area intensity near 2θ = 30.1° at the peak top of the main peak of the cubic system, I y represents the peak area intensity near 2θ = 29.2° at the peak top of the main peak of yttrium oxide not dissolved in zirconia.)

[0042] [5] The zirconia pre-sintered body according to [3] or [4], wherein the standard deviation of the yttrium element distribution is 2 mol% or more and less than 21 mol%.

[0043] [6] The zirconia pre-sintered body according to [4] or [5], which satisfies the foregoing condition (A-1) or (A-2), and the proportion of yttrium oxide not dissolved in zirconia is 1 to 25%.

[0044] [7] The zirconia pre-sintered body according to [4] or [5], which satisfies the aforementioned condition (A-3) or (A-4), and a part of the aforementioned yttrium oxide is yttrium oxide not dissolved in zirconia, and the proportion of the yttrium oxide not dissolved in zirconia is 1 to 15%.

[0045] [8] The zirconia pre-sintered body according to any one of [1] to [7], wherein the content rate of the aforementioned stabilizer is 2 to 9 mol% based on the total moles of zirconia and the stabilizer.

[0046] [9] The zirconia pre-sintered body according to any one of [1] to [8], having a density of 3.6 g / cm 3 or less.

[0047]

[10] The zirconia pre-sintered body according to any one of [1] to [9], having an average primary particle diameter of 40 to 110 nm.

[0048]

[11] A zirconia composition, which contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia,

[0049] ΔL of the first sintered body produced by sintering the aforementioned zirconia composition at 1550 °C for 120 minutes 1 *(W-B) and ΔL of the second sintered body produced by sintering at 1550 °C for 10 minutes 2 *(W-B) satisfies the following formula (1) when compared.

[0050] ΔL 2 *(W-B) / ΔL 1 *(W-B) ≥ 0.85 (1)

[0051]

[12] The zirconia composition according to

[11] , which satisfies any one of the following conditions (i) or (ii).

[0052] (i) The aforementioned zirconia contains tetragonal zirconia powder (T), and a part of the aforementioned stabilizer is stabilizer powder not dissolved in zirconia; or

[0053] (ii) The aforementioned zirconia contains monoclinic zirconia powder (M) and cubic zirconia powder (C).

[0054]

[13] The zirconia composition according to

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

[0055]

[14] The zirconia composition according to

[13] , wherein the ratio of the total mass of the aforementioned zirconia powder (T) and the aforementioned 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.

[0056]

[15] The zirconia composition according to

[13] or

[14] , wherein the aforementioned zirconia powder (M) is 0 to 85% by mass in the total mass of the zirconia powder (T) and the zirconia powder (M).

[0057]

[16] The zirconia composition according to any one of

[12] to

[15] , wherein the aforementioned zirconia powder (T) contains a stabilizer that has been dissolved and can inhibit the phase transformation of zirconia, and the content rate of the aforementioned dissolved stabilizer is 2 to 4 mol% relative to the total moles of zirconia and the stabilizer.

[0058]

[17] The zirconia composition according to

[12] , which satisfies the aforementioned condition (ii), and furthermore, a part of the aforementioned stabilizer is a stabilizer that is not dissolved in zirconia.

[0059]

[18] The zirconia composition according to

[12] or

[17] , wherein the ratio of the total mass of the aforementioned zirconia powder (M) and the aforementioned 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.

[0060]

[19] The zirconia composition according to

[12] ,

[17] or

[18] , wherein the aforementioned zirconia powder (C) is 15.0 to 95.0% by mass in the total mass of the aforementioned zirconia powder (M) and the aforementioned zirconia powder (C).

[0061]

[20] The zirconia composition according to any one of

[12] ,

[17] to

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

[0062]

[21] The zirconia composition according to any one of

[12] ,

[17] to

[20] , wherein the aforementioned zirconia powder (C) contains a stabilizer that has been dissolved and can inhibit the phase transformation of zirconia, and the content rate of the aforementioned dissolved stabilizer is 5 mol% or more and 15 mol% or less relative to the total moles of the aforementioned zirconia powder (C) and the stabilizer.

[0063]

[22] The zirconia composition according to

[12] , which satisfies the aforementioned condition (i), further contains cubic zirconia powder (T), and the ratio of the total mass of zirconia powder (T) and the aforementioned 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.

[0064]

[23] The zirconia composition according to any one of

[11] to

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

[0065]

[24] A method for manufacturing a zirconia pre-sintered body, wherein the zirconia composition described in

[11] to

[23] is calcined to such an extent that zirconia particles do not reach sintering with each other.

[0066]

[25] A method for manufacturing a zirconia sintered body, wherein the zirconia pre-sintered body described in [1] to

[10] is sintered.

[0067] Advantages of the Invention

[0068] By using the zirconia pre-sintered body and composition of the present invention, and their manufacturing methods, it is possible to obtain a zirconia sintered body that can maintain the same high light transmittance as that of long-time sintering after short-time sintering with a holding time of 10 minutes or less at the highest sintering temperature.

[0069] In addition, by using the zirconia pre-sintered body and composition of the present invention, and their manufacturing methods, it is possible to obtain a zirconia sintered body that can maintain the same high light transmittance as that of long-time sintering after short-time sintering with a highest sintering temperature lower than 1600 °C (particularly preferably 1560 °C or lower) and a holding time of 10 minutes or less at the highest sintering temperature. Therefore, the manufacturing efficiency is excellent and it is industrially advantageous. Detailed Embodiments

[0070] The zirconia pre-sintered body of the present invention contains zirconia and a stabilizer capable of suppressing the phase transformation of zirconia. The ΔL 1 *(W - B) of the first sintered body fabricated by sintering at 1550 °C for 120 minutes and the ΔL 2 *(W - B) of the second sintered body fabricated by sintering at 1550 °C for 10 minutes satisfy the following formula (1) when compared.

[0071] ΔL 2 *(W - B) / ΔL 1 *(W - B) ≥ 0.85 (1)

[0072] The zirconia pre-sintered body can be a precursor (intermediate product) of the zirconia sintered body. In this specification, the zirconia pre-sintered body refers to a substance in which zirconia particles are consolidated with each other to an extent that does not reach sintering.

[0073] "To an extent that does not reach sintering" means an unsintered state (semi-sintered state). In the case of a sintered body in a fully sintered state, as sintering progresses, the relative density increases and densification occurs. Therefore, the relative density of the zirconia sintered body is 95% or more. The relative density can be calculated in the form of the ratio of the measured density obtained by the Archimedes method to the theoretical density.

[0074] It should be noted that in this specification, the upper limit value and the lower limit value of a numerical range (such as the content rate of each component, the value calculated from each component, and each physical property, etc.) can be appropriately combined.

[0075] In addition, in this specification, the tetragonal ratio f t , cubic ratio f c , monoclinic ratio f m , and the content rate f y of yttrium oxide not dissolved in zirconia, the total amount of which does not exceed 100%.

[0076] [Zirconia pre-sintered body]

[0077] The zirconia pre-sintered body of the present invention contains zirconia and a stabilizer (hereinafter also simply referred to as "stabilizer") that can inhibit the phase transformation of zirconia.

[0078] Examples of such stabilizers include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y 2 O 3、 hereinafter also referred to as "yttrium oxide"), cerium oxide (CeO 2 ), scandium oxide (Sc 2 O 3 ), niobium oxide (Nb 2 O 5 ), lanthanum oxide (La 2 O 3 ), erbium oxide (Er 2 O 3 ), praseodymium oxide (Pr 2 O 3 , Pr 6 O 11 ), samarium oxide (Sm 2 O 3 ), europium oxide (Eu 2 O 3 ), thulium oxide (Tm 2 O 3 ), gallium oxide (Ga2 O 3 )), indium oxide (In 2 O 3 ), ytterbium oxide (Yb 2 O 3 ), etc. oxides, preferably yttrium oxide. The stabilizer can be compounded alone with 1 kind, or can be compounded in combination with 2 or more kinds.

[0079] The content rate of the stabilizer in the zirconia pre-sintered body of the present invention is preferably 2 mol% or more, more preferably 3 mol% or more, further preferably 3.5 mol% or more, and particularly preferably 4 mol% or more with respect to the total moles of zirconia (zirconium(IV); ZrO 2 ). In the case of 2 mol% or more, it is preferable from the viewpoint that the cubic crystal system in the crystal form contained in the zirconia sintered body increases and the light transmittance improves.

[0080] In addition, from the viewpoint of being able to suppress the decrease in the strength of the sintered body, the content rate of the aforementioned stabilizer is preferably 9 mol% or less, more preferably 8 mol% or less, further preferably 7.5 mol% or less, and particularly preferably 7 mol% or less.

[0081] The content rate of the aforementioned stabilizer can be set to a range composed of any combination of them. For example, the content rate of the aforementioned stabilizer is preferably 2 - 9 mol%, more preferably 3 - 8 mol%, further preferably 3.5 - 7.5 mol%, and particularly preferably 4 - 7 mol%.

[0082] The content rate of the stabilizer in the zirconia pre-sintered body of the present invention can be adjusted by adjusting the content rate of the un-dissolved stabilizer in the zirconia composition described later, or by adjusting the content rate of the cubic zirconia with a high content rate of the stabilizer dissolved in zirconia, etc., and also by changing the compounding ratio after considering the content rate of the stabilizer dissolved in each crystal system.

[0083] In this specification, the content rate of the stabilizer means the total content rate of the stabilizer dissolved in zirconia and the stabilizer not dissolved in zirconia.

[0084] The content rate of the stabilizer in the zirconia pre-sintered body of the present invention can be measured by, for example, inductively coupled plasma (ICP; Inductively Coupled Plasma) optical emission spectrometry, X-ray fluorescence analysis (XRF), etc.

[0085] The ΔL 1 *(W - B) of the first sintered body produced by sintering the zirconia pre-sintered body of the present invention at 1550 °C for 120 minutes and the ΔL2 When comparing *(W - B), the following formula (1) is satisfied.

[0086] ΔL 2 *(W - B) / ΔL 1 *(W - B) ≥ 0.85 (1)

[0087] ΔL of the first sintered body 1 *(W - B) and ΔL of the second sintered body 2 *(W - B) are both values calculated using the L* value of the brightness (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 brightness L* value can be measured using, for example, a spectrocolorimeter manufactured by Olympus Corporation (product name "Crystaleye"), a spectrocolorimeter CM-3610A or CM-36dGV manufactured by Konica Minolta, Inc., and measured using a D65 light source.

[0088] Regarding ΔL of the first sintered body 1 *(W - B) and ΔL of the second sintered body 2 *(W - B), the brightness (LW*) measured with the background of the sample (zirconia sintered body) set to white and the brightness (LB*) measured with the same sample for LW* on a black background using the same measuring device, measuring mode, and light source are both measured, and the difference between the two (ΔL* = (LW*) - (LB*)) is an index of translucency.

[0089] In the evaluation of ΔL of the first sintered body 1 *(W - B) and ΔL of the second sintered body 2 *(W - B), the maximum sintering temperature is 1550°C in both cases, and the heating rate and cooling rate are the same.

[0090] In the evaluation of ΔL of the first sintered body 1 *(W - B), the holding time (residence time) at the maximum sintering temperature is 120 minutes (hereinafter, sintering with a holding time of 120 minutes at the maximum sintering temperature is also referred to as "120-minute sintering" or "long-time sintering").

[0091] In the evaluation of ΔL of the second sintered body 2 *(W - B), the holding time (residence time) at the maximum sintering temperature is 10 minutes (hereinafter, calcination with a holding time of 10 minutes at the maximum sintering temperature is also referred to as "10-minute sintering" or "short-time sintering").

[0092] As a reason for the zirconia pre-sintered body of the present invention to be able to maintain a high light transmittance equivalent to that of long-time sintering even after short-time sintering with a holding time of 10 minutes or less at the highest sintering temperature, the following reasons can be considered.

[0093] Hereinafter, the case where the stabilizer is yttrium oxide will be described as an example, but the present invention is not limited to the case where the stabilizer is yttrium oxide.

[0094] Generally, if the holding time at the highest sintering temperature is shortened to 10 minutes, in the crystal system of zirconia, when the concentration gradient of the metal element (preferably yttrium element) of the stabilizer is small, almost no movement of yttrium element or yttrium ions between substances occurs. Therefore, there are difficulties caused by 10-minute sintering such as insufficient energy stabilization accompanied by substance movement, insufficient sintering, and reduced light transmittance.

[0095] In contrast, as shown in the embodiments described in any of the following conditions (i) or (ii) (for example, conditions (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6), etc.), specific crystal systems of zirconia powder and yttrium oxide powder are selected according to the amount of yttrium oxide dissolved, etc., to form a pre-sintered body, so that there is a supply source of yttrium element or yttrium ions and a movement destination where yttrium element or yttrium ions move within the zirconia pre-sintered body system. A moderate concentration gradient of yttrium element or yttrium ions is achieved between the two, and yttrium element or yttrium ions move between the crystals in the zirconia crystal system during sintering.

[0096] It can be considered that by having a crystal system of zirconia or a yttrium source as a supply source of yttrium element or yttrium ions and a crystal system of zirconia as a movement destination where yttrium element or yttrium ions can move within the zirconia pre-sintered body system in this way, the concentration difference of yttrium element or yttrium ions between substances existing in the system during sintering is increased, and substance movement occurs while the particles are consolidated with each other during sintering. Thus, even in short-time sintering of 10 minutes or less, the movement of yttrium element or yttrium ions is sufficiently carried out. When combined with raw material powder having a specified average particle size, it acts integrally, and in the obtained zirconia sintered body, the yttrium element is more uniformly distributed, and the light transmittance of the zirconia sintered body satisfies the above formula (1).

[0097] Patent Document 3 discloses an example in which the holding time at the highest sintering temperature can be shortened to 2 minutes only when using zirconia powder in which the yttrium dissolved in zirconia is 4 mol% or more and 5.5 mol% or less.

[0098] However, in Patent Document 3, the embodiment capable of shortening the holding time does not disperse the undissolved yttrium compound to the outermost surface of the zirconia particles like other embodiments, but is achieved by the following method: on the basis of only using yttrium dissolved in zirconia, performing CIP treatment multiple times (specifically 5 to 10 times), thereby reducing the porosity of the workpiece to be cut. Furthermore, sintering is performed at a high temperature with the maximum sintering temperature set at 1600°C. In this way, considering industrial applicability, the manufacturing efficiency difference between the manufacturing method of obtaining a workpiece to be cut by performing CIP treatment more than 5 times and the high-temperature treatment with a maximum sintering temperature of 1600°C is disadvantageous industrially from the cost aspect, and there is room for improvement.

[0099] In contrast, as described above, in the present invention, by increasing the concentration difference of yttrium element or yttrium ions between the substances present in the system during sintering, the mass transfer occurring during sintering is promoted, so that in a short-time sintering of 10 minutes or less, furthermore, even if the maximum sintering temperature is lower than 1600°C, the light transmittance is excellent. Therefore, when manufacturing a molded body, repeated CIP treatment more than 5 times is not necessary as in Patent Document 3, and the maximum sintering temperature is lower and the sintering time is short. Therefore, both the reduction of the maximum sintering temperature and the shortening of the sintering time are achieved, which is industrially advantageous.

[0100] In the present invention, for crystal systems different from those of Patent Document 3 (for example, crystal systems in which the content of monoclinic crystal in zirconia constituting the zirconia pre-sintered body is 55% or more), as long as the movement of yttrium element or yttrium ions can be promoted, the effects of the present invention can be exerted.

[0101] As described above, in the present invention, even when using yttrium oxide not dissolved in zirconia (hereinafter also referred to as "undissolved yttrium oxide"), the effects of the present invention can be exerted. This is an advantage different from Patent Document 3, and Reference Example 1 of Patent Document 3 shows that if less than 4 mol% of dissolved yttrium is not used, the amount of dissolved yttrium is insufficient, and phase transformation cannot be sufficiently assisted by short-time sintering, and sufficient light transmittance cannot be obtained.

[0102] Hereinafter, as a suitable embodiment, the case where the stabilizer is yttrium oxide will be described as an example.

[0103] The present invention is not limited to the case where the stabilizer is yttrium oxide. Therefore, when using other stabilizers, the "yttrium oxide content" can be understood as the content of other stabilizers, and the "yttrium element distribution" can be understood as the element distribution of other metal elements.

[0104] In the zirconia pre-sintered body of the present invention, from the viewpoint that yttrium element or yttrium ions are likely to move during short-time sintering and the obtained zirconia sintered body has excellent light transmittance, the standard deviation of the yttrium element distribution is preferably 2 mol% or more, more preferably 2.1 mol% or more, further preferably 2.5 mol% or more, and particularly preferably 3 mol% or more.

[0105] In addition, regarding the standard deviation of the yttrium element distribution mentioned above, from the viewpoint that yttrium element or yttrium ions are likely to move between substances present in the system during short-time sintering and the obtained zirconia sintered body has more excellent light transmittance, it is preferably less than 21 mol%, more preferably 20 mol% or less, further preferably 18 mol% or less, and particularly preferably 15 mol% or less.

[0106] The standard deviation of the yttrium element distribution mentioned above can be set to a range composed of any combination of them. For example, the standard deviation of the yttrium element distribution mentioned above is preferably 2 mol% or more and less than 21 mol%, more preferably 2.1 mol% or more and 20 mol% or less, further preferably 2.5 mol% or more and 18 mol% or less, and particularly preferably 3 mol% or more and 15 mol% or less.

[0107] As a suitable embodiment, a zirconia pre-sintered body can be cited, in which the standard deviation of the yttrium element distribution is 2.1 mol% or more and 15 mol% or less.

[0108] The standard deviation of the yttrium element distribution mentioned above can be adjusted by the content f of un-dissolved yttrium oxide y , the specified average particle size of the raw material powder used as the yttrium source, the content of the specified raw material powder in the raw material composition, the mixing ratio, etc. In particular, it can be adjusted more simply by the content f of un-dissolved yttrium oxide y and the specified average particle size of the raw material powder used as the yttrium source.

[0109] The calculation method of the standard deviation of the yttrium element distribution is as described in the following examples.

[0110] In the zirconia pre-sintered body of the present invention, from the viewpoint that yttrium element or yttrium ions are likely to move during short-time sintering and the obtained zirconia sintered body has excellent light transmittance, it is preferably a zirconia pre-sintered body that satisfies any one of the following conditions (i) or (ii).

[0111] (i) The aforementioned zirconia contains tetragonal zirconia, and a part of the aforementioned stabilizer is a stabilizer that is not dissolved in zirconia; or

[0112] (ii) The aforementioned zirconia contains monoclinic zirconia and cubic zirconia.

[0113] As an embodiment of condition (i), for example, a zirconia pre-sintered body can be cited, wherein the aforementioned zirconia contains only tetragonal zirconia, and a part of the aforementioned stabilizer is a stabilizer that is not dissolved in zirconia; a zirconia pre-sintered body, wherein the aforementioned zirconia contains monoclinic zirconia and tetragonal zirconia, and a part of the aforementioned stabilizer is a stabilizer that is not dissolved in zirconia; a zirconia pre-sintered body, wherein the aforementioned zirconia contains tetragonal zirconia and cubic zirconia, and a part of the aforementioned stabilizer is a stabilizer that is not dissolved in zirconia.

[0114] As an embodiment of condition (i), specifically, a zirconia pre-sintered body that satisfies any one of the following conditions (A-1) or (A-2), (A-5) or (A-6) can be cited.

[0115] As an embodiment of condition (ii), specifically, a zirconia pre-sintered body that preferably satisfies any one of the following conditions (A-3) or (A-4) is preferred.

[0116] It should be noted that in any embodiment, the content ratio of yttrium oxide, the standard deviation of the yttrium element distribution, etc. can be appropriately combined and selected within the ranges described in this specification.

[0117] (A-1) The aforementioned zirconia contains monoclinic zirconia and tetragonal zirconia, the content ratio of the monoclinic phase is 55% or more, the content ratio of the tetragonal phase is 10% or more, and a part of the aforementioned yttrium oxide is yttrium oxide that is not dissolved in zirconia;

[0118] (A-2) The aforementioned zirconia contains tetragonal zirconia, does not conform to (A-1), the content ratio of the tetragonal phase is 10% or more, and a part of the aforementioned yttrium oxide is yttrium oxide that is not dissolved in zirconia;

[0119] (A-3) The aforementioned zirconia contains monoclinic zirconia and cubic zirconia, and the content ratio of the monoclinic phase is 55% or more, and the content ratio of the cubic phase is 15% or more;

[0120] (A-4) The aforementioned zirconia contains monoclinic zirconia and cubic zirconia, does not conform to (A-3), and the content ratio of the cubic phase is 15% or more;

[0121] (A-5) The aforementioned zirconia contains tetragonal zirconia and cubic zirconia, the content ratio of the tetragonal phase is 5% or more and less than 50%, the content ratio of the cubic phase is 50% or more and less than 95%, and a part of the aforementioned yttrium oxide is yttrium oxide that is not dissolved in zirconia;

[0122] (A-6) The aforementioned zirconia contains tetragonal zirconia and cubic zirconia, and does not meet (A-5). The content rate of the aforementioned cubic zirconia is 10% or more and less than 50%, and a part of the aforementioned yttrium oxide is yttrium oxide that is not dissolved in zirconia.

[0123] The content rates of the tetragonal system, cubic system, and monoclinic system in the aforementioned (A-1), (A-2), (A-3), (A-4), (A-5), or (A-6) are calculated according to the following formulas, respectively.

[0124] Tetragonal ratio f t (%) = I t / (I m + I t + I c + I y ) × 100 (2-1)

[0125] Cubic ratio f c (%) = I c / (I m + I t + I c + I y ) × 100 (2-2)

[0126] Monoclinic ratio f m (%) = I m / (I m + I t + I c + I y ) × 100 (2-3)

[0127] (In the formula, 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 area intensity of the peak near 2θ = 28.2° at the peak top of the main peak of the monoclinic system, I t represents the area intensity of the peak near 2θ = 30.2° at the peak top of the main peak of the tetragonal system, I c represents the area intensity of the peak near 2θ = 30.1° at the peak top of the main peak of the cubic system, I y represents the area intensity of the peak near 2θ = 29.2° at the peak top of the main peak of the undissolved yttrium oxide.)

[0128] Hereinafter, for the embodiments (A-1), (A-2), (A-3), (A-4), (A-5), and (A-6), as examples suitable for the embodiments, the embodiments will be described separately.

[0129] It should be noted that the content ratios of the tetragonal system, cubic system, and monoclinic system in the embodiments (A-1), (A-2), (A-3), (A-4), (A-5), and (A-6) are calculated according to the above formulas (2-1), (2-2), and (2-3), respectively. The measurement methods for the content ratios of the tetragonal system, cubic system, and monoclinic system are as described in the examples below.

[0130] <Embodiment (A-1)>

[0131] As a suitable embodiment (A-1), a zirconia pre-sintered body can be cited, in which zirconia contains monoclinic zirconia and tetragonal zirconia.

[0132] The content ratio of the aforementioned monoclinic system is 55% or more, the content ratio of the aforementioned tetragonal system is 10% or more, and a part of the aforementioned yttrium oxide is yttrium oxide that is not dissolved in zirconia (hereinafter also referred to as "Embodiment (A-1)").

[0133] In Embodiment (A-1), the content ratio of the monoclinic system is preferably 55% or more, more preferably 56% or more, further preferably 58% or more, and particularly preferably 60% or more.

[0134] In addition, the content ratio of the aforementioned monoclinic system is preferably 85% or less, more preferably 80% or less, further preferably 75% or less, and particularly preferably 70% or less.

[0135] The content ratio of the aforementioned monoclinic system can be set to a range composed of any combination of them. For example, the content ratio of the aforementioned monoclinic system is preferably 55% or more and 85% or less, more preferably 56% or more and 80% or less, further preferably 58% or more and 75% or less, and particularly preferably 60% or more and 70% or less.

[0136] When the content ratio of the monoclinic system is within the aforementioned range and combined with tetragonal zirconia with a specified content ratio, the concentration difference of yttrium elements or yttrium ions in the system during sintering can be set to a desired range. When combined with raw material powders having a specified average particle size, they act together. In a short-time sintering of 10 minutes or less, the movement of metal elements or their ions constituting the stabilizer is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0137] It should be noted that in this specification, the aforementioned concentration difference is not particularly limited as long as it is within a range where a desired standard deviation can be obtained in the sintered zirconia sintered body and a range where translucency satisfying formula (1) can be obtained.

[0138] The measurement method for the content ratio of the monoclinic system is as described in the examples below.

[0139] In the embodiment (A-1), the content rate of the tetragonal system is preferably 10% or more, more preferably 15% or more, still more preferably 20% or more, and particularly preferably 25% or more.

[0140] In addition, the content rate of the tetragonal system is preferably 44% or less, more preferably 42% or less, still more preferably 40% or less, and particularly preferably 38% or less.

[0141] The content rate of the tetragonal system may be set to a range composed of any combination thereof. For example, the content rate of the tetragonal system is preferably 10% or more and 44% or less, more preferably 15% or more and 42% or less, still more preferably 20% or more and 40% or less, and particularly preferably 25% or more and 38% or less.

[0142] When the content rate of the tetragonal system is within the above range, when combined with monoclinic zirconia supplied as the moving destination of yttrium element or yttrium ion, the concentration difference of the metal element or its ion constituting the stabilizing agent in the system during sintering can be set to a desired range. When combined with raw material powder having a specified average particle size, it acts integrally, and the movement of the metal element or its ion constituting the stabilizing agent is sufficiently carried out even in short-time sintering of 10 minutes or less, and the obtained zirconia sintered body has excellent translucency.

[0143] The measurement method of the content rate of the tetragonal system is as described in the following examples.

[0144] As another preferred embodiment, a zirconia pre-sintered body can be cited, in which the content rate of the monoclinic system is 55% or more and 75% or less, and the content rate of the tetragonal system is 25% or more and 45% or less.

[0145] In the embodiment (A-1), as still another preferred embodiment, a zirconia pre-sintered body can be cited, in which the proportion of yttrium oxide not dissolved in zirconia is 1 to 25%.

[0146] In the zirconia pre-sintered body according to the embodiment (A-1), the proportion of yttrium oxide not dissolved in zirconia (hereinafter also referred to as "content rate f of undissolved yttrium oxide" y " or "f y ") can be calculated according to the following formula (2-4).

[0147] f y (%) = I y / (I m + I t + I c + I y ) × 100 (2-4)

[0148] (In the formula, f y represents the proportion (%) of yttrium oxide not in solid solution. In XRD measurement, I m represents the area intensity of the peak near 2θ = 28.2° at the peak top of the main peak of the monoclinic system, I t represents the area intensity of the peak near 2θ = 30.2° at the peak top of the main peak of the tetragonal system, I c represents the area intensity of the peak near 2θ = 30.1° at the peak top of the main peak of the cubic system, I y represents the area intensity of the peak near 2θ = 29.2° at the peak top of the main peak of yttrium oxide not in solid solution.)

[0149] In the embodiment (A-1), in the case of combining tetragonal zirconia and monoclinic zirconia, the concentration gradient of yttrium element can be set within a desired range. From the viewpoint that yttrium element is likely to move even during short-time sintering and the obtained zirconia sintered body has excellent light transmittance, the content f of yttrium oxide not in solid solution y is preferably 1% or more, more preferably 2% or more, further preferably 3% or more, and particularly preferably 3.5% or more.

[0150] In addition, from the viewpoint of being able to suppress the reduction in the strength of the sintered body, the content f of yttrium oxide not in solid solution y is preferably 25% or less, and from the viewpoints of being able to reduce the standard deviation of the yttrium element distribution, yttrium element is likely to move during short-time sintering, and the obtained zirconia sintered body has more excellent light transmittance, it is more preferably 20% or less, further preferably 18% or less, and particularly preferably 16% or less.

[0151] The content f of the aforementioned yttrium oxide not in solid solution y can be set to a range composed of any combination of them. For example, the content f of the aforementioned yttrium oxide not in solid solution y is preferably 1 to 25%, more preferably 2 to 20%, further preferably 3 to 18%, and particularly preferably 3.5 to 16%.

[0152] The content f of the aforementioned yttrium oxide not in solid solution y can be adjusted by the specified average particle size of the yttrium oxide powder used as the yttrium source, the content of the specified yttrium oxide powder in the raw material composition, the mixing ratio, etc.

[0153] In the embodiment (A-1), the zirconia in the zirconia pre-sintered body may contain the cubic system. From the viewpoint of easily promoting the movement of yttrium element or yttrium ions, it is preferably free of the cubic system. In other words, in the embodiment (A-1), it is preferred that the cubic system and the tetragonal system do not coexist in the zirconia pre-sintered body.

[0154] <Embodiment (A-2)>

[0155] As a suitable embodiment (A-2), a zirconia pre-sintered body can be cited. Among them, the zirconia contains tetragonal zirconia, does not conform to (A-1), the content rate of the aforementioned tetragonal phase is 10% or more, and a part of the aforementioned yttrium oxide is yttrium oxide not dissolved in zirconia (hereinafter also referred to as "Embodiment (A-2)").

[0156] In Embodiment (A-2), the zirconia in the zirconia pre-sintered body contains a tetragonal phase. The content rate of the tetragonal phase is preferably 10% or more, more preferably 15% or more, further preferably 20% or more, and particularly preferably 25% or more.

[0157] In addition, from the viewpoint of being able to suppress the reduction in the strength of the sintered body, the content rate of the aforementioned tetragonal phase is preferably less than 98%, more preferably 97.5% or less, further preferably 97% or less, and particularly preferably 96.5% or less.

[0158] The content rate of the aforementioned tetragonal phase can be set to a range composed of any combination of them. For example, the content rate of the aforementioned tetragonal phase is preferably 10% or more and 98% or less, more preferably 15% or more and 97.5% or less, further preferably 20% or more and 97% or less, and particularly preferably 25% or more and 96.5% or less.

[0159] As another embodiment, it does not contain monoclinic zirconia. For example, the content rate of the aforementioned tetragonal phase is preferably more than 45% and less than 98%, more preferably 55% or more and 97.5% or less, further preferably 70% or more and 97% or less, and particularly preferably 80% or more and 96.5% or less.

[0160] When the content rate of the tetragonal phase is within the aforementioned range, when combined with undissolved yttrium oxide, the concentration difference of yttrium elements or yttrium ions in the system during sintering can be set to a desired range. When combined with raw material powders having a specified average particle size, they act together. In a short-time sintering of 10 minutes or less, the movement of metal elements or their ions constituting the stabilizer is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0161] The method for measuring the content rate of the tetragonal phase is as described in the following examples.

[0162] Since Embodiment (A-2) does not conform to (A-1), the content rate of the monoclinic phase is 0% or more and less than 55%.

[0163] The content rate of the monoclinic phase is preferably 1% or more, more preferably 2% or more, further preferably 2.5% or more, and particularly preferably 10% or more.

[0164] In addition, the content rate of the monoclinic system is preferably less than 55%, more preferably 50% or less, still more preferably 40% or less, and particularly preferably 30% or less.

[0165] The content rate of the monoclinic system can be set to a range composed of any combination thereof. For example, the content rate of the monoclinic system is preferably 1% or more and less than 55%, more preferably 2% or more and 50% or less, still more preferably 2.5% or more and 40% or less, and particularly preferably 10% or more and 30% or less.

[0166] As another preferred embodiment, a zirconia pre-sintered body can be cited, wherein the zirconia in the zirconia pre-sintered body contains a tetragonal system, the content rate of the monoclinic system is 0%, the content rate of the tetragonal system is 80% or more and 97% or less, and a part of the stabilizer is a stabilizer not dissolved in zirconia.

[0167] In addition, in Embodiment (A-2), among the yttrium oxides contained in the zirconia pre-sintered body, a part of the stabilizer is undissolved yttrium oxide.

[0168] In the zirconia pre-sintered body according to Embodiment (A-2), the content rate f of undissolved yttrium oxide y can be calculated according to the above formula (2-4).

[0169] In Embodiment (A-2), from the viewpoints of being able to set the concentration gradient of yttrium element to a desired range when combined with tetragonal zirconia, being liable to move the yttrium element during short-time sintering, and the obtained zirconia sintered body having excellent translucency, the content rate f of undissolved yttrium oxide y is preferably more than 2%, more preferably 2.5% or more, still more preferably 3% or more, and particularly preferably 3.5% or more.

[0170] In addition, from the viewpoint of being able to suppress a decrease in the strength of the sintered body, the content rate f of undissolved yttrium oxide y is preferably 25% or less, and from the viewpoints of being able to reduce the standard deviation of the yttrium element distribution, being liable to move the yttrium element during short-time sintering, and the obtained zirconia sintered body having more excellent translucency, it is more preferably 20% or less, still more preferably 18% or less, and particularly preferably 16% or less.

[0171] The content rate f of the undissolved yttrium oxide y can be set to a range composed of any combination thereof. For example, the content rate f of the undissolved yttrium oxide y is preferably 1 to 25%, more preferably 2 to 20%, still more preferably 3 to 18%, and particularly preferably 3.5 to 16%.

[0172] In the embodiment (A-2), the zirconia in the pre-sintered zirconia body may contain cubic crystal system, and from the viewpoint of facilitating the movement of yttrium element or yttrium ion, it is preferably free of cubic crystal system. In other words, in the embodiment (A-2), it is preferable that the cubic crystal system and the tetragonal crystal system do not coexist in the pre-sintered zirconia body.

[0173] <Embodiment (A-3)>

[0174] As a suitable embodiment (A-3), a pre-sintered zirconia body can be cited, in which the zirconia contains monoclinic zirconia and cubic zirconia.

[0175] The content rate of the aforementioned monoclinic crystal system is 55% or more, and the content rate of the aforementioned cubic crystal system is 15% or more (hereinafter also referred to as "embodiment (A-3)").

[0176] In the embodiment (A-3), the content rate of the monoclinic crystal system is preferably 55% or more, more preferably 56% or more, further preferably 58% or more, and particularly preferably 60% or more.

[0177] In addition, the content rate of the aforementioned monoclinic crystal system is preferably 85% or less, more preferably 80% or less, further preferably 75% or less, and particularly preferably 70% or less.

[0178] The content rate of the aforementioned monoclinic crystal system can be set to a range composed of any combination of them. For example, the content rate of the aforementioned monoclinic crystal system is preferably 55% or more and 85% or less, more preferably 56% or more and 80% or less, further preferably 58% or more and 75% or less, and particularly preferably 60% or more and 70% or less.

[0179] When the content rate of the monoclinic crystal system is within the aforementioned range, and when cubic zirconia with a specified content rate is further combined with yttrium oxide not dissolved as needed, the concentration difference of yttrium element or yttrium ion in the system during sintering can be set to a desired range. When combined with raw material powder having a specified average particle size, it acts integrally. In a short-time sintering of 10 minutes or less, the movement of the metal element or its ion constituting the stabilizer is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0180] The measurement method of the content rate of the monoclinic crystal system is as described in the following examples.

[0181] In the embodiment (A-3), the content rate of the cubic crystal system is preferably 15% or more, more preferably 18% or more, further preferably 20% or more, and particularly preferably 25% or more.

[0182] In addition, the content ratio of the cubic system is preferably 44% or less, more preferably 42% or less, still more preferably 40% or less, and particularly preferably 38% or less.

[0183] The content ratio of the cubic system may be in a range composed of any combination thereof. For example, the content ratio of the cubic system is preferably 15% or more and 44% or less, more preferably 15% or more and 42% or less, still more preferably 20% or more and 40% or less, and particularly preferably 25% or more and 38% or less.

[0184] When the content ratio of the cubic system is within the above range, when combined with monoclinic zirconia that exists as a migration destination of yttrium element or yttrium ion, the concentration difference of the metal element or its ion that constitutes the stabilizer in the system during sintering can be set to a desired range. When combined with raw material powder having a specified average particle size, it acts integrally. During short-time sintering of 10 minutes or less, the migration of the metal element or its ion that constitutes the stabilizer is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0185] The method for measuring the content ratio of the cubic system is as described in the following examples.

[0186] In the embodiment (A-3), as another suitable embodiment, a zirconia pre-sintered body can be cited, in which a part of yttrium oxide is yttrium oxide not dissolved in zirconia, and the ratio of the yttrium oxide not dissolved in zirconia is 1 to 15%.

[0187] In the zirconia pre-sintered body according to the embodiment (A-3), the content ratio f of the undissolved yttrium oxide y can be calculated according to the above formula (2-4).

[0188] In the embodiment (A-3), from the viewpoints that when combining cubic zirconia and monoclinic zirconia, the concentration gradient of yttrium element can be set to a desired range, the migration of yttrium element is likely to occur during short-time sintering, and the obtained zirconia sintered body has excellent translucency, the content ratio f of the undissolved yttrium oxide y is preferably 1% or more, more preferably 2% or more, still more preferably 3% or more, and particularly preferably 3.5% or more.

[0189] In addition, from the viewpoint of being able to suppress the reduction of the strength of the sintered body, the content ratio f of the undissolved yttrium oxide y is preferably 15% or less, and from the viewpoints of being able to reduce the standard deviation of the yttrium element distribution, the migration of yttrium element is likely to occur during short-time sintering, and the obtained zirconia sintered body has more excellent translucency, it is more preferably 14% or less, still more preferably 12% or less, and particularly preferably 11% or less.

[0190] The content fraction f of the un-dissolved yttrium oxide described above y It can be set as a range formed by any combination of them. For example, the content fraction f of the un-dissolved yttrium oxide described above y is preferably 1 to 15%, more preferably 2 to 14%, still more preferably 3 to 12%, and particularly preferably 3.5 to 11%.

[0191] In the embodiment (A-3), the zirconia in the pre-sintered zirconia body may contain tetragonal zirconia. From the viewpoint of facilitating the movement of yttrium element or yttrium ion, it is preferably free of tetragonal zirconia. In other words, in the embodiment (A-3), it is preferred that cubic zirconia and tetragonal zirconia do not coexist in the pre-sintered zirconia body.

[0192] <Embodiment (A-4)>

[0193] As a suitable embodiment (A-4), a pre-sintered zirconia body can be cited, in which the zirconia contains cubic zirconia and monoclinic zirconia, does not conform to (A-3), and the content fraction of the cubic zirconia is 15% or more (hereinafter also referred to as "embodiment (A-4)").

[0194] In the embodiment (A-4), the zirconia in the pre-sintered zirconia body contains cubic zirconia. The content fraction of the cubic zirconia is preferably 15% or more, more preferably 20% or more, still more preferably 30% or more, and particularly preferably 40% or more.

[0195] In addition, the content fraction of the cubic zirconia is preferably 98% or less, more preferably 97% or less, still more preferably 96.5% or less, and particularly preferably 96% or less.

[0196] The content fraction of the cubic zirconia can be set as a range formed by any combination of them. For example, the content fraction of the cubic zirconia is preferably 15% or more and 98% or less, more preferably 20% or more and 97% or less, still more preferably 30% or more and 96.5% or less, and particularly preferably 40% or more and 96% or less.

[0197] When the content fraction of the cubic zirconia is within the above range, when combined with monoclinic zirconia supplied as the movement destination of yttrium element or yttrium ion, the concentration difference of the metal element or its ion constituting the stabilizer in the system during sintering can be set to a desired range. When combined with raw material powder having a specified average particle size, it acts integrally, and during short-time sintering of 10 minutes or less, the movement of the metal element or its ion constituting the stabilizer is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0198] The method for measuring the content fraction of the cubic zirconia is as described in the following examples.

[0199] In the embodiment (A-4), the zirconia in the pre-sintered zirconia body contains monoclinic zirconia. The content rate of the monoclinic system is preferably 1% or more, more preferably 2% or more, still more preferably 2.5% or more, and particularly preferably 3% or more.

[0200] In addition, the content rate of the aforementioned monoclinic system is preferably less than 55%, more preferably 50% or less, still more preferably 45% or less, and particularly preferably 40% or less.

[0201] The content rate of the aforementioned monoclinic system can be set to a range composed of any combination of them. For example, the content rate of the aforementioned monoclinic system is preferably 1% or more and less than 55%, more preferably 2% or more and 50% or less, still more preferably 2.5% or more and 45% or less, and particularly preferably 3% or more and 40% or less.

[0202] When the content rate of the monoclinic system is within the aforementioned range, when further combining cubic zirconia as a supply source of yttrium element or yttrium ion with yttrium oxide not dissolved in solid solution as needed, the concentration difference of the metal element or its ion constituting the stabilizing agent in the system during sintering can be set to a desired range. When combined with raw material powder having a specified average particle size, it functions integrally, and in a short-time sintering of 10 minutes or less, the movement of the metal element or its ion constituting the stabilizing agent is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0203] The measurement method of the content rate of the monoclinic system is as described in the following examples.

[0204] In the embodiment (A-4), as another suitable embodiment, a pre-sintered zirconia body can be cited, in which the zirconia contains cubic zirconia and monoclinic zirconia, the content rate of the cubic system is 40% or more and 90% or less, and the content rate of the aforementioned monoclinic system is 10% or more and less than 55%.

[0205] In the embodiment (A-4), as another suitable embodiment, a pre-sintered zirconia body can be cited, in which the zirconia contains cubic zirconia and monoclinic zirconia, the content rate of the cubic system is 70% or more and 97% or less, and the content rate of the aforementioned monoclinic system is 3% or more and 30% or less.

[0206] In the embodiment (A-4), as another suitable embodiment, a pre-sintered zirconia body can be cited, in which a part of the yttrium oxide is yttrium oxide not dissolved in solid solution in the zirconia, and the ratio of the yttrium oxide not dissolved in solid solution in the zirconia is 1 to 15%.

[0207] In the pre-sintered zirconia body according to the embodiment (A-4), the content rate f of the yttrium oxide not dissolved in solid solutiony It can be calculated according to the above formula (2-4).

[0208] In Embodiment (A-4), from the viewpoints that when cubic zirconia and monoclinic zirconia are combined, the concentration gradient of yttrium element can be set within a desired range, the movement of yttrium element is likely to occur during short-time sintering, and the obtained zirconia sintered body has excellent translucency, the content ratio f of yttrium oxide not dissolved y is preferably 1% or more, more preferably 2% or more, further preferably 3% or more, and particularly preferably 3.5% or more.

[0209] In addition, from the viewpoint of being able to suppress the reduction in the strength of the sintered body, the content ratio f of yttrium oxide not dissolved y is preferably 15% or less. From the viewpoints of being able to reduce the standard deviation of the yttrium element distribution, the movement of the yttrium element is likely to occur during short-time sintering, and the obtained zirconia sintered body has more excellent translucency, it is more preferably 14% or less, further preferably 12% or less, and particularly preferably 11% or less.

[0210] The aforementioned content ratio f of yttrium oxide not dissolved y can be set to a range composed of any combination thereof. For example, the aforementioned content ratio f of yttrium oxide not dissolved y is preferably 1 to 15%, more preferably 2 to 14%, further preferably 3 to 12%, and particularly preferably 3.5 to 11%.

[0211] In Embodiment (A-4), the zirconia in the zirconia pre-sintered body may contain tetragonal zirconia. From the viewpoint of easily promoting the movement of yttrium element or yttrium ions, it is preferably free of tetragonal zirconia. In other words, in Embodiment (A-4), it is preferable that cubic zirconia and tetragonal zirconia do not coexist in the zirconia pre-sintered body.

[0212] <Embodiment (A-5)>

[0213] As a certain suitable Embodiment (A-5), a zirconia pre-sintered body can be cited, in which the zirconia contains tetragonal zirconia and cubic zirconia,

[0214] the content ratio of the aforementioned tetragonal zirconia is 5% or more and less than 50%, the content ratio of the aforementioned cubic zirconia is 50% or more and less than 95%, and a part of the aforementioned yttrium oxide is yttrium oxide not dissolved in zirconia (hereinafter also referred to as "Embodiment (A-5)").

[0215] In Embodiment (A-5), the content ratio of tetragonal zirconia is preferably 6% or more, more preferably 8% or more, further preferably 9% or more, and particularly preferably 10% or more.

[0216] In addition, the content ratio of the tetragonal system is preferably less than 49%, more preferably less than 48%, still more preferably less than 46%, and particularly preferably less than 40%.

[0217] The content ratio of the tetragonal system can be set to a range composed of any combination thereof.

[0218] For example, in a certain embodiment, the content ratio of the tetragonal system is preferably 6% or more and less than 49%, more preferably 8% or more and less than 48%, still more preferably 9% or more and less than 46%, and particularly preferably 10% or more and less than 40%.

[0219] When the content ratio of the tetragonal system is within the foregoing range, when combining cubic zirconia with a specified content ratio and yttrium oxide not in solid solution, the concentration difference of yttrium element or yttrium ions in the system during sintering can be set to a desired range. When combined with raw material powder having a specified average particle size, it acts integrally. In a short-time sintering of 10 minutes or less, the movement of the metal element or its ions constituting the stabilizer is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0220] The measurement method of the content ratio of the tetragonal system is as described in the following examples.

[0221] In Embodiment (A-5), the content ratio of the cubic system is preferably 51% or more, more preferably 52% or more, still more preferably 54% or more, and particularly preferably 60% or more.

[0222] In addition, the content ratio of the cubic system is preferably less than 94%, more preferably less than 92%, still more preferably less than 91%, and particularly preferably less than 90%.

[0223] The content ratio of the cubic system can be set to a range composed of any combination thereof. For example, the content ratio of the cubic system is preferably 51% or more and less than 94%, more preferably 52% or more and less than 92%, still more preferably 54% or more and less than 91%, and particularly preferably 60% or more and less than 90%.

[0224] When the content ratio of the cubic system is within the foregoing range, when combining yttrium oxide not in solid solution with tetragonal zirconia existing as the movement destination of yttrium element or yttrium ions, the concentration difference of the metal element or its ions constituting the stabilizer in the system during sintering can be set to a desired range. When combined with raw material powder having a specified average particle size, it acts integrally. In a short-time sintering of 10 minutes or less, the movement of the metal element or its ions constituting the stabilizer is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0225] The method for measuring the content ratio of the cubic system is as described in the following examples.

[0226] In addition, in Embodiment (A-5), among the yttrium oxides contained in the zirconia green compact, a part of the stabilizer is yttrium oxide that is not dissolved.

[0227] In the zirconia green compact according to Embodiment (A-5), the content ratio f of the undissolved yttrium oxide y can be calculated according to the above formula (2-4).

[0228] In Embodiment (A-5), from the viewpoints of being able to set the concentration gradient of yttrium element within a desired range when combining cubic zirconia and tetragonal zirconia, facilitating the movement of yttrium element during short-time sintering, and the obtained zirconia sintered body having excellent translucency, the content ratio f of the undissolved yttrium oxide y is preferably 0.001% or more, more preferably 0.01% or more, further preferably 0.02% or more, particularly preferably 0.05% or more, and most preferably 0.1% or more.

[0229] In addition, from the viewpoint of being able to suppress the reduction in the strength of the sintered body, the content ratio f of the undissolved yttrium oxide y is preferably 12% or less, and from the viewpoints of being able to reduce the standard deviation of the yttrium element distribution, facilitating the movement of yttrium element during short-time sintering, and the obtained zirconia sintered body having more excellent translucency, it is more preferably 10% or less, further preferably 9% or less, particularly preferably 8% or less, and most preferably 5% or less.

[0230] The content ratio f of the aforementioned undissolved yttrium oxide y can be set to a range composed of any combination thereof. For example, the content ratio f of the aforementioned undissolved yttrium oxide y is preferably 0.001 - 12%, more preferably 0.01 - 10%, further preferably 0.02 - 9%, particularly preferably 0.05 - 8%, and most preferably 0.1 - 5%.

[0231] In Embodiment (A-5), from the viewpoint of easily promoting the movement of yttrium element or yttrium ions, the zirconia in the zirconia green compact preferably does not contain monoclinic system.

[0232] <Embodiment (A-6)>

[0233] As a suitable Embodiment (A-6), a zirconia green compact can be cited, in which the zirconia contains tetragonal zirconia and cubic zirconia, does not conform to (A-5), the content ratio of the aforementioned cubic system is 10% or more and less than 50%, and a part of the aforementioned yttrium oxide is yttrium oxide that is not dissolved in zirconia (hereinafter also referred to as "Embodiment (A-6)").

[0234] Embodiment (A-6) does not conform to (A-5), and thus, the content rate of the tetragonal system is 50% or more and less than 90%.

[0235] In Embodiment (A-6), the content rate of the tetragonal system is preferably 51% or more, more preferably 52% or more, further preferably 54% or more, and particularly preferably 60% or more.

[0236] In addition, the content rate of the aforementioned tetragonal system is preferably less than 89%, more preferably less than 88%, further preferably less than 86%, and particularly preferably less than 85%.

[0237] The content rate of the aforementioned tetragonal system can be set to a range composed of a combination of values within any of them.

[0238] For example, in a certain embodiment, the content rate of the aforementioned tetragonal system is preferably 51% or more and less than 89%, more preferably 52% or more and less than 88%, further preferably 54% or more and less than 86%, and particularly preferably 60% or more and less than 85%.

[0239] When the content rate of the tetragonal system is within the aforementioned range, when combining cubic zirconia with a specified content rate and yttrium oxide not in solid solution, the concentration difference of yttrium elements or yttrium ions in the system during sintering can be set to a desired range. When combined with raw material powder having a specified average particle size, it acts integrally. In short-time sintering of 10 minutes or less, the movement of metal elements or their ions constituting the stabilizer is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0240] The method for measuring the content rate of the tetragonal system is as described in the following examples.

[0241] In Embodiment (A-6), the content rate of the cubic system is preferably 11% or more, more preferably 12% or more, further preferably 14% or more, and particularly preferably 15% or more.

[0242] In addition, the content rate of the aforementioned cubic system is preferably less than 49%, more preferably less than 48%, further preferably less than 46%, and particularly preferably less than 40%.

[0243] The content rate of the aforementioned cubic system can be set to a range composed of any combination of them. For example, the content rate of the aforementioned cubic system is preferably 11% or more and less than 49%, more preferably 12% or more and less than 48%, further preferably 14% or more and less than 46%, and particularly preferably 15% or more and less than 40%.

[0244] When the content rate of the cubic system is within the aforementioned range, when combining undissolved yttrium oxide with tetragonal zirconia existing as the migration destination of yttrium element or yttrium ion, the concentration difference of the metal element or its ion constituting the stabilizer in the system during sintering can be set within a desired range. When combined with raw material powder having a specified average particle size, it functions integrally. During short-time sintering of 10 minutes or less, the migration of the metal element or its ion constituting the stabilizer is also sufficiently carried out, and the obtained zirconia sintered body has excellent translucency.

[0245] The measurement method of the content rate of the cubic system is as described in the following examples.

[0246] In addition, in Embodiment (A-6), among the yttrium oxide contained in the zirconia pre-sintered body, a part of the stabilizer is undissolved yttrium oxide.

[0247] In the zirconia pre-sintered body according to Embodiment (A-6), the content rate f of undissolved yttrium oxide y can be calculated according to the above formula (2-4).

[0248] In Embodiment (A-6), from the viewpoints that the concentration gradient of yttrium element can be set within a desired range when combining cubic zirconia and tetragonal zirconia, the migration of yttrium element is likely to occur during short-time sintering, and the obtained zirconia sintered body has excellent translucency, the content rate f of undissolved yttrium oxide y is preferably 0.001% or more, more preferably 0.01% or more, further preferably 0.02% or more, particularly preferably 0.05% or more, and most preferably 0.1% or more.

[0249] In addition, from the viewpoint of being able to suppress the reduction of the strength of the sintered body, the content rate f of undissolved yttrium oxide y is preferably 12% or less. From the viewpoints of being able to reduce the standard deviation of the yttrium element distribution, the migration of yttrium element is likely to occur during short-time sintering, and the obtained zirconia sintered body has more excellent translucency, it is more preferably 10% or less, further preferably 9% or less, particularly preferably 8% or less, and most preferably 5% or less.

[0250] The content rate f of the aforementioned undissolved yttrium oxide y can be set to a range composed of any combination of them. For example, the content rate f of the aforementioned undissolved yttrium oxide y is preferably 0.001 - 12%, more preferably 0.01 - 10%, further preferably 0.02 - 9%, particularly preferably 0.05 - 8%, and most preferably 0.1 - 5%.

[0251] In the embodiment (A-6), from the viewpoint of facilitating the movement of yttrium element or yttrium ion, it is preferable that the zirconia in the zirconia green compact does not contain monoclinic system.

[0252] In the embodiments (A-1) to (A-6), by using yttrium oxide as the stabilizer and making the standard deviation of the yttrium element distribution be 2 mol% or more and less than 21 mol%, the movement of the yttrium element or yttrium ion between substances in the system during sintering is sufficiently carried out even in short-time sintering of 10 minutes or less, and the light transmittance of the obtained zirconia sintered body can satisfy the above formula (1).

[0253] As the zirconia green compact of the present invention, as described above, from the viewpoint of easily obtaining the range of the standard deviation of the desired yttrium element distribution, it is preferably a zirconia green compact that does not contain, for example, zirconia with only tetragonal system and cubic system zirconia, and does not contain a stabilizer that is not dissolved in zirconia; zirconia with only cubic system zirconia, and a part of the stabilizer is a stabilizer that is not dissolved in zirconia; zirconia with only cubic system zirconia, and does not contain a stabilizer that is not dissolved in zirconia; zirconia containing monoclinic system zirconia and tetragonal system zirconia, and does not contain a stabilizer that is not dissolved in zirconia; zirconia with only tetragonal system zirconia, and does not contain a stabilizer that is not dissolved in zirconia.

[0254] In addition, as an embodiment, it is possible not to contain a zirconia green compact with a porosity of 15 to 30%. The aforementioned porosity is a value calculated according to the following formula.

[0255] Porosity (%) = Pore volume / (Pore volume + Skeleton volume) × 100

[0256] The pore volume is a value determined by measuring the connected pores without closed pores having a diameter of about 5 nm to 250 μm using the mercury intrusion method. The skeleton volume is a value calculated based on the true density measured by the gas displacement method. The aforementioned skeleton volume is calculated according to the skeleton volume (cm 3 / g) = 1 / True density (g / cm 3 )

[0257] The pore volume and the skeleton volume can be measured as follows: A zirconia green compact machined into a prism shape (5 mm × 5 mm × 5 mm) is used as a sample. For the pore volume, it is measured using a fully automatic multifunctional mercury intrusion porosimeter (POREMASTER, manufactured by Anton Paar, Japan) (measurement conditions: mercury surface tension: 480 erg / cm 2, Contact angle: 140°, drainage contact angle: 140°, pressure: 0 to 50000 psia). Regarding the skeletal volume, the true density can be measured using a dry-type automatic densitometer (AccuPyc II 1340, manufactured by Shimadzu Corporation) and then calculated.

[0258] The density of the zirconia pre-sintered body of the present invention is preferably 3.6 g / cm 3 Hereinafter, more preferably 3.5 g / cm 3 Hereinafter, even more preferably 3.4 g / cm 3 Hereinafter.

[0259] In addition, the density of the zirconia pre-sintered body of the present invention is preferably 2.5 g / cm 3 or more, more preferably 2.7 g / cm 3 or more, even more preferably 2.9 g / cm 3 or more.

[0260] The density of the zirconia pre-sintered body can be calculated by (the mass of the zirconia pre-sintered body) / (the volume of the zirconia pre-sintered body). Regarding the density of the zirconia pre-sintered body, for example, while changing the cut-out position of the zirconia pre-sintered body, test pieces with a size of 10 mm square are cut out from any part (n = 3), the mass and volume of the obtained test pieces are measured, the average value of the measured values is calculated, and the density is calculated using the average value according to the above formula.

[0261] The average primary particle size of the particles in the zirconia pre-sintered 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.

[0262] In addition, the average primary particle size of the particles in the zirconia pre-sintered 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.

[0263] The average primary particle size of the particles in the aforementioned zirconia pre-sintered body can be set to a range composed of any combination thereof. For example, the aforementioned average primary particle size is preferably 40 to 110 nm, more preferably 45 to 105 nm, and even more preferably 50 to 100 nm.

[0264] The method for measuring the average primary particle size of the particles in the zirconia pre-sintered body is as described in the following examples.

[0265] As long as the zirconia pre-sintered body of the present invention exhibits the effects of the present invention, it may contain additives other than zirconia and stabilizers. Examples of such additives include coloring agents (including pigments, composite pigments, and fluorescent agents), binders, dispersants, emulsifiers, defoamers, pH regulators, lubricants, light transmittance regulators, etc. The additives can be used alone or in combination of two or more.

[0266] As the aforementioned pigment, oxides of at least one element selected from the group consisting of, for example, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Er can be cited.

[0267] As the aforementioned composite pigment, for example, (Zr, V)O 2 , Fe(Fe, Cr) 2 O 4 , (Ni, Co, Fe)(Fe, Cr) 2 O 4 ·ZrSiO 4 , (Co, Zn)Al 2 O 4 etc.

[0268] The zirconia pre-sintered body of the present invention may contain a fluorescent agent. By including a fluorescent agent in the zirconia pre-sintered body, the zirconia sintered body has fluorescence. The type of the fluorescent agent is not particularly limited, and one or more than two kinds of fluorescent agents capable of emitting fluorescence using light of any wavelength can be used.

[0269] As the fluorescent agent, a fluorescent agent containing a metal element can be cited. As the metal element, for example, Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Tm, etc. can be cited. The fluorescent agent may contain one of these metal elements alone, or may contain two or more. Among these metal elements, Ga, Bi, Eu, Gd, Tm are preferred, and Bi, Eu are more preferred.

[0270] As the fluorescent agent, for example, oxides, hydroxides, acetates, nitrates, etc. of the above-mentioned metal elements can be cited. In addition, the fluorescent agent may be Y 2 SiO 5 : Ce, Y 2 SiO 5 : Tb, (Y, Gd, Eu)BO 3 , Y 2 O 3 : Eu, YAG: Ce, ZnGa 2 O 4 : Zn, BaMgAl 10 O 17 : Eu, etc.

[0271] The content rate of the fluorescent agent in the zirconia pre-sintered body is not particularly limited and can be appropriately adjusted according to the type of the fluorescent agent or the use of the zirconia sintered body, etc. From the viewpoint of being preferably used as a dental prosthesis, etc., based on 100% by mass of zirconia contained in the zirconia pre-sintered body, in terms of conversion to the oxide of the metal element contained in the fluorescent agent, it is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and further preferably 0.01% by mass or more.

[0272] In addition, the content rate of the fluorescent agent, in terms of conversion to the oxide of the metal element contained in the fluorescent agent, is preferably 1% by mass or less, more preferably 0.5% by mass or less, and further preferably 0.1% by mass or less. By making the content rate above the above lower limit, the fluorescence is not inferior even compared with human natural teeth. In addition, by making the content rate below the above upper limit, a decrease in light transmittance and mechanical strength can be suppressed.

[0273] Examples of the binder include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, ethyl cellulose, etc. In order to improve the light transmittance, the content rate 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 further preferably 3% by mass or less based on 100% by mass of zirconia.

[0274] Examples of the plasticizer include polyethylene glycol, glycerin, propylene glycol, dibutyl phthalate, etc.

[0275] Examples of the dispersant include ammonium polycarboxylate (such as ammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylate copolymer, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (such as polyoxyethylene lauryl ether phosphate and other polyoxyethylene alkyl ether phosphates), nonionic surfactants, olein glyceride, amine salt type surfactants, oligoglycols, stearic acid, etc.

[0276] Examples of the emulsifier include alkyl ethers, phenyl ethers, sorbitan derivatives, ammonium salts, etc.

[0277] Examples of the defoamer include alcohols, polyethers, polyethylene glycols, silicones, waxes, etc.

[0278] Examples of the pH adjuster include ammonia, ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide), etc.

[0279] Examples of the lubricant include polyoxyethylene alkylated ethers, waxes, etc.

[0280] Examples of the light transmittance regulator include alumina (Al 2 O3 ) Titanium oxide (TiO 2 ), silicon dioxide (SiO 2 ), zircon, lithium silicate, lithium disilicate, etc.

[0281] [Method for manufacturing a zirconia pre-sintered body]

[0282] The zirconia pre-sintered body of the present invention can be manufactured by calcining (pre-sintering) a zirconia composition (e.g., a formed body) to such an extent that zirconia particles do not reach sintering with each other.

[0283] In this specification, a zirconia composition is a composition containing zirconia powder and a stabilizer powder capable of suppressing the phase transformation of zirconia.

[0284] The zirconia composition can be, for example, a formed body that has been formed.

[0285] The formed body is formed by applying an external force to a powder containing zirconia-based particles. The zirconia composition and the zirconia formed body are objects before calcination, and thus it means that they have not necked (fixed).

[0286] As an embodiment, a zirconia composition can be cited, which is a zirconia composition containing zirconia and a stabilizer capable of suppressing the phase transformation of zirconia.

[0287] When comparing ΔL 1 *(W - B) of the first sintered body produced by sintering the aforementioned zirconia composition at 1550°C for 120 minutes with ΔL 2 *(W - B) of the second sintered body produced by sintering at 1550°C for 10 minutes, the following formula (1) is satisfied.

[0288] ΔL 2 *(W - B) / ΔL 1 *(W - B)≥0.85 (1)

[0289] Regarding ΔL 1 *(W - B) and ΔL 2 *(W - B), as described in the zirconia pre-sintered body.

[0290] By pre-sintering the zirconia composition to remove organic substances, a zirconia pre-sintered body in which a desired amount of stabilizer is dissolved in zirconia and the primary particles have necked can be obtained.

[0291] From the viewpoints of being able to obtain excellent translucency in a short time in the subsequent sintering process, being able to remove organic substances, and not causing adverse effects on the subsequent sintering process, the calcination temperature (pre-sintering temperature) of the zirconia composition is preferably 200°C or higher, more preferably 300°C or higher, and further preferably 400°C or higher.

[0292] In addition, the pre-sintering temperature is preferably 900 °C or lower, more preferably 700 °C or lower, and still more preferably 600 °C or lower.

[0293] The pre-sintering temperature can be set to a range composed of any combination thereof. For example, the pre-sintering temperature is preferably 200 to 900 °C, more preferably 300 to 700 °C, and still more preferably 400 to 600 °C.

[0294] The pressure during pre-sintering is not particularly limited and can be normal pressure.

[0295] The time for treatment at the aforementioned pre-sintering temperature (pre-sintering time) is preferably 30 minutes or more, more preferably 120 minutes or more. By setting it to 120 minutes or more, organic substances can be removed, and adverse effects in the subsequent sintering process can be easily avoided.

[0296] In addition, the pre-sintering time is preferably 360 minutes or less, more preferably 240 minutes or less. By setting it to 240 minutes or less, the diffusion distance of the stabilizer can be suppressed, and the concentration gradient of the stabilizer can be maintained. Therefore, it is preferable from the viewpoint of being able to obtain excellent light transmittance in a short time in the subsequent sintering process.

[0297] The pre-sintering time can be set to a range composed of any combination thereof. For example, the pre-sintering time is preferably 30 to 360 minutes, more preferably 120 to 240 minutes.

[0298] [Manufacturing method of zirconia composition]

[0299] Examples of the manufacturing method of the zirconia composition include the following manufacturing method, which includes: a step of manufacturing zirconia powder; a step of manufacturing a stabilizer powder (hereinafter also referred to as "stabilizer powder") capable of suppressing the phase change of zirconia; and a step of mixing the zirconia powder and the stabilizer powder to manufacture a powder containing zirconia-based particles.

[0300] In this specification, particles containing zirconia particles and stabilizer particles are referred to as "zirconia-based particles".

[0301] · Manufacturing methods of zirconia powder and stabilizer powder

[0302] The preparation methods of zirconia powder and yttrium oxide powder as raw material powders are not particularly limited, and for example, a breakdown process of pulverizing and disintegrating coarse particles for fine powdering; a building up process of synthesizing from atoms to ions through a nucleation and growth process, etc. can be adopted.

[0303] Examples of the zirconia powder described above include tetragonal zirconia powder (T), monoclinic zirconia powder (M), and cubic zirconia powder (C).

[0304] From the viewpoint of excellent translucency of the zirconia pre-sintered body obtained by short-time sintering, the average primary particle diameter (r1) of the above zirconia powder (hereinafter also referred to as "average particle diameter (r1)") is preferably 40 nm or more, more preferably 45 nm or more, and further preferably 50 nm or more.

[0305] In addition, from the viewpoint of excellent translucency of the zirconia pre-sintered body obtained by short-time sintering, the average particle diameter (r1) of the zirconia powder is preferably 110 nm or less, more preferably 105 nm or less, and further preferably 100 nm or less.

[0306] The average particle diameter (r1) of the zirconia powder can be set to a range composed of any combination of them. For example, the average particle diameter (r1) of the zirconia powder (tetragonal zirconia powder (T), cubic zirconia powder (C), and monoclinic zirconia powder (M)) is preferably 40 to 110 nm, more preferably 45 to 105 nm, and further preferably 50 to 100 nm.

[0307] By making the average particle diameters of the tetragonal zirconia powder (T), monoclinic zirconia powder (M), and cubic zirconia powder (C) fall within the above average particle diameter (r1) range, when a specific crystal system is selected and used, the movement of the metal element or its ion constituting the stabilizer is sufficiently carried out even in short-time sintering of 10 minutes or less, and the obtained zirconia sintered body has excellent translucency.

[0308] From the viewpoint of excellent translucency of the zirconia pre-sintered body obtained by short-time sintering, 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, further preferably 45 nm or more, and particularly preferably 50 nm or more.

[0309] In addition, from the viewpoint of excellent translucency of the zirconia pre-sintered body obtained by short-time sintering, the average particle diameter (r2) of the stabilizer powder is preferably 350 nm or less, more preferably 300 nm or less, further preferably 250 nm or less, and particularly preferably 200 nm or less.

[0310] The average particle size (r2) of the stabilizer powder can be set to a range composed of any combination of them. For example, the average particle size (r1) of the zirconia powder is preferably 20 to 350 nm, more preferably 40 to 300 nm, further preferably 45 to 250 nm, particularly preferably 50 to 200 nm, and most preferably 60 to 110 nm.

[0311] By making the average particle size (r2) of the stabilizer powder fall within the aforementioned range, when combined with the zirconia powder having a specific crystal system and the aforementioned specified average particle size (r1), the movement of the metal element or its ions constituting the stabilizer is sufficiently carried out even in short-time sintering of 10 minutes or less, and the resulting zirconia sintered body has excellent translucency.

[0312] In a certain embodiment, the average particle size (r2) of the stabilizer powder can exceed 60 nm. As this embodiment, for example, a zirconia composition in which the average particle size (r2) of the stabilizer powder exceeds 60 nm and is 300 nm or less can be cited.

[0313] The aforementioned average particle size (r1) and average particle size (r2) are average primary particle sizes. For example, a laser diffraction / scattering type particle size distribution measuring device (trade name “Partica LA-950”) manufactured by Horiba, Ltd. can be used to perform ultrasonic irradiation on the diluted slurry with water for 30 minutes, and then measure it on a volume basis while contacting the ultrasonic wave.

[0314] Hereinafter, the preparation method of the zirconia powder will be described by way of example. The preparation method of the zirconia powder can also be used in the same way for the preparation method of the stabilizer particles except in the case of special description.

[0315] As a certain suitable embodiment, a zirconia composition that satisfies any one of the following conditions (i) or (ii) can be cited.

[0316] (i) The aforementioned zirconia contains tetragonal zirconia powder (T), and a part of the aforementioned stabilizer is stabilizer powder that is not dissolved in zirconia; or

[0317] (ii) The aforementioned zirconia contains monoclinic zirconia powder (M) and cubic zirconia powder (C).

[0318] As a suitable embodiment that satisfies the aforementioned condition (i), for example, a zirconia composition can be cited. In this composition, the aforementioned zirconia only contains tetragonal zirconia powder (T), and a part of the aforementioned stabilizer is stabilizer powder that is not dissolved in zirconia; a zirconia composition, in which the aforementioned zirconia contains monoclinic zirconia powder (M) and tetragonal zirconia powder (T), and a part of the aforementioned stabilizer is stabilizer powder that is not dissolved in zirconia; a zirconia composition, in which the aforementioned zirconia contains tetragonal zirconia powder (T) and cubic zirconia powder (C), and a part of the aforementioned stabilizer is stabilizer powder that is not dissolved in zirconia.

[0319] In addition, as another suitable embodiment, a zirconia composition can be cited. It satisfies the aforementioned condition (i) and further contains monoclinic zirconia powder (M).

[0320] In addition, as another suitable embodiment, a zirconia composition can be cited. It satisfies the aforementioned condition (ii), and furthermore, a part of the aforementioned stabilizer is a stabilizer that is not dissolved in zirconia.

[0321] As zirconia raw materials for manufacturing zirconia powder, tetragonal zirconia, monoclinic zirconia, and cubic zirconia can be used respectively. These zirconia raw materials can use, for example, raw materials manufactured by the manufacturing method described in Japanese Patent No. 6543926 (raw materials manufactured by hydrolysis reaction). In addition, these zirconia raw materials can use commercially available products respectively.

[0322] As commercially available products, for example, zirconia powder "TZ-0" (monoclinic 0Y (yttrium oxide is 0 mol%)), zirconia powder "TZ-3Y-E" (tetragonal 3Y) in which 3 mol% of yttrium oxide is dissolved, zirconia powder "TZ-6Y" (cubic 6Y) in which 6 mol% of yttrium oxide is dissolved, and zirconia powder "TZ-10Y" (cubic 10Y) in which 10 mol% of yttrium oxide is dissolved can be cited. The above are manufactured by Tosoh Corporation, etc.

[0323] As a pulverization process, the coarse particles of the zirconia raw materials can be pulverized separately by crystal system to separately produce tetragonal zirconia powder (T), monoclinic zirconia powder (M), and cubic zirconia powder (C) adjusted to be within the range of the aforementioned average particle size (r2).

[0324] In addition, from the viewpoint of easily controlling the desired average particle sizes (r1) and (r2), it is preferable to pulverize the zirconia raw materials separately from the raw materials of the stabilizer powder (such as yttrium oxide raw materials) to produce zirconia powder.

[0325] Regarding the stabilizer powder, the raw material compound (e.g., yttrium oxide) can be pulverized by using a known method (e.g., a ball mill) to adjust it to the aforementioned average particle size (r2). It suffices to be able to adjust it to within the range of the aforementioned average particle size (r2) by pulverization, and thus, the average particle size of the raw material compound is not particularly limited.

[0326] The zirconia powder having the aforementioned average particle size (r1) and the stabilizer powder having the aforementioned average particle size (r2) can be adjusted to the average particle size by a known method such as pulverizing the raw material powder.

[0327] From the viewpoint of easily adjusting to the aforementioned specified average particle size (r1) and average particle size (r2), it is preferable to use a pulverizing medium of a small size for pulverization. For example, it is preferable to use a pulverizing medium of 100 μm or less.

[0328] In addition, it is preferable that: after pulverizing the coarse particles, the obtained zirconia powder is classified.

[0329] Classification can be performed using a known method and apparatus. As a known method, for example, elutriation (washing) can be performed by utilizing the difference in sedimentation velocity caused by the dispersibility depending on the particle size, or a centrifuge can be used for it to accelerate sedimentation. As a known apparatus, for example, a porous membrane (a membrane filter having a pore size of 100 nm, etc.), a classification apparatus (a wet classification apparatus, a dry classification apparatus), etc. can be cited.

[0330] As needed, including changing the pulverization time, etc., by operations such as pulverization and classification, a raw material powder having a desired average particle size can be produced.

[0331] By producing a raw material powder having a desired average particle size, for the crystal system of zirconia, when selecting a specified crystal system and / or when yttrium oxide is not solid-solved, it is easy to set the concentration gradient of yttrium element or yttrium ion within a specified range. As a result, it can be considered that: during sintering, the particles are consolidated with each other while mass transfer occurs, and thus, during short-time sintering of 10 minutes or less, the movement of yttrium element or yttrium ion is also sufficiently performed, and in the obtained zirconia sintered body, the yttrium element is more uniformly distributed, and the translucency of the zirconia sintered body satisfies the above formula (1).

[0332] In addition, hereinafter, the case where the stabilizer is yttrium oxide will be described as an example, but the present invention is not limited to the case where the stabilizer is yttrium oxide.

[0333] As the zirconia raw material, the content rate of yttrium oxide solid-solved in tetragonal zirconia (hereinafter also referred to as "the solid solution amount of yttrium oxide") is preferably 2 mol% or more, more preferably 2.2 mol% or more, and further preferably 2.5 mol% or more with respect to the total moles of zirconia and yttrium oxide.

[0334] In addition, the solid solution amount of yttrium oxide in the aforementioned tetragonal zirconia is preferably less than 5 mol%, more preferably 4.8 mol% or less, still more preferably 4.5 mol% or less, particularly preferably 4.0 mol% or less, and most preferably 3.8 mol% or less.

[0335] The solid solution amount of yttrium oxide in the aforementioned tetragonal zirconia can be set to a range composed of any combination thereof. For example, the solid solution amount of yttrium oxide in the aforementioned tetragonal zirconia is preferably more than 2 mol% and 5 mol% or less, more preferably 2.0 mol% or more and 4.8 mol% or less, still 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.

[0336] The solid solution amount of yttrium oxide in the tetragonal zirconia powder (T) obtained from the zirconia raw material is also the same as the solid solution amount of yttrium oxide in the zirconia raw material.

[0337] The solid solution amount of yttrium oxide in the monoclinic zirconia used in the present invention is preferably 0 to 1 mol%, more preferably 0 to 0.5 mol%, and still more preferably 0 mol% relative to the total moles of zirconia and yttrium.

[0338] The solid solution amount of yttrium oxide in the monoclinic zirconia powder (M) obtained from the zirconia raw material is also the same as the solid solution amount of yttrium oxide in the zirconia raw material.

[0339] As the zirconia raw material, the solid solution amount of yttrium oxide in cubic zirconia is preferably 5 mol% or more, more preferably 5.5 mol% or more, and still more preferably 6 mol% or more relative to the total moles of zirconia and yttrium.

[0340] In addition, the solid solution amount of yttrium oxide in the aforementioned cubic zirconia is preferably 15 mol% or less, more preferably 12 mol% or less, and still more preferably 10 mol% or less.

[0341] The solid solution amount of yttrium oxide in the aforementioned cubic zirconia can be set to a range composed of any combination thereof. For example, the solid solution amount of yttrium oxide in the aforementioned cubic zirconia is preferably more than 5 mol% and 15 mol% or less, more preferably 5.5 mol% or more and 12 mol% or less, and still more preferably 6 mol% or more and 10 mol% or less.

[0342] The solid solution amount of yttrium oxide in the cubic zirconia powder (C) obtained from the zirconia raw material is also the same as the solid solution amount of yttrium oxide in the zirconia raw material.

[0343] As a method for measuring the solid solution amount of yttrium oxide in zirconia of the tetragonal system, monoclinic system, and cubic system, it can be measured by, for example, inductively coupled plasma (ICP) optical emission spectrometry, X-ray fluorescence analysis (XRF), etc.

[0344] As long as the zirconia composition of the present invention exhibits the effects of the present invention, it may contain additives other than zirconia and a stabilizer. Examples of such additives include colorants (including pigments, composite pigments, and fluorescent agents), binders, dispersants, emulsifiers, defoamers, pH adjusters, lubricants, alumina (Al 2 O 3 ), titanium oxide (TiO 2 ), silicon dioxide (SiO 2 ), etc. The additives may be used alone or in combination of two or more. Examples of the additives include the same substances as those exemplified for the zirconia pre-sintered body.

[0345] The aforementioned additives may be added during the mixing or pulverization of the raw materials, or may be added to the pulverized powder.

[0346] In the production of the zirconia composition of the present invention, the mixing of the zirconia powder and the stabilizer powder may be dry mixing or wet mixing.

[0347] The mixing ratio of the zirconia powder and the stabilizer powder can be appropriately adjusted according to the embodiment (for example, embodiments (A-1) to (A-6), etc.) so as to achieve the desired crystal system content ratio.

[0348] For example, in the zirconia composition that satisfies condition (i), when further containing monoclinic zirconia powder (M) as needed, the ratio of the total mass of the zirconia powder (T) and the aforementioned 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.

[0349] In addition, in the zirconia composition that satisfies condition (i), the contents of the zirconia powder (T) and the aforementioned zirconia powder (M) can be adjusted within the aforementioned range to obtain the tetragonal system content ratio and monoclinic system content ratio in embodiments (A-1) and (A-2).

[0350] Further, as a certain embodiment, in the zirconia composition satisfying condition (i), when the zirconia composition contains zirconia powder (M) as in Embodiments (A-1) and (A-2), the content of zirconia powder (M) in the zirconia composition is preferably 0 to 85% by mass, more preferably 0 to 82% by mass, and still more preferably 0 to 80% by mass in the total mass of zirconia powder (T) and zirconia powder (M).

[0351] As the zirconia composition satisfying condition (i), zirconia powder (T) preferably contains a stabilizer that has been dissolved and can inhibit the phase transformation of zirconia.

[0352] Further, the content of the stabilizer that has been dissolved and can inhibit the phase transformation of zirconia in zirconia powder (T) is preferably 2 to 4 mol%, more preferably 2 to 3.5 mol%, and still more preferably 2 to 3 mol% relative to the total moles of zirconia and the stabilizer.

[0353] Further, in the zirconia composition satisfying condition (ii), the ratio of the total mass of zirconia powder (M) and the aforementioned 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.

[0354] Further, in the zirconia composition satisfying condition (ii), the contents of zirconia powder (M) and the aforementioned zirconia powder (C) can be adjusted within the aforementioned ranges to obtain the content of monoclinic phase and the content of cubic phase in Embodiments (A-3) and (A-4).

[0355] Further, as a certain embodiment, the content of zirconia powder (C) in the zirconia composition satisfying condition (ii) is preferably 15.0 to 95.0% by mass, more preferably 18.0 to 82.0% by mass, and still more preferably 20.0 to 80.0% by mass in the total mass of the aforementioned zirconia powder (M) and the aforementioned zirconia powder (C).

[0356] In the zirconia composition satisfying condition (ii), the content of the stabilizer that has been dissolved and can inhibit the phase transformation of zirconia in zirconia powder (M) is preferably 0 to 1 mol%, more preferably 0 to 0.5 mol%, and still more preferably 0 mol% relative to the total moles of zirconia and the stabilizer.

[0357] In the zirconia composition satisfying condition (ii), the content ratio of the stabilizer that has been dissolved in the zirconia powder (C) and can inhibit the phase transition of zirconia is preferably 5 mol% or more and 15 mol% or less, more preferably 5.5 mol% or more and 12 mol% or less, and still more preferably 6 mol% or more and 10 mol% or less, relative to the total moles of zirconia and the stabilizer.

[0358] In addition, in the zirconia composition satisfying condition (i), when cubic zirconia powder (T) is further included as needed, the ratio of the total mass of the zirconia powder (T) and the aforementioned 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%, still 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%.

[0359] In addition, in the zirconia composition satisfying condition (i), when cubic zirconia powder (T) is further included as needed, the contents of the zirconia powder (T) and the aforementioned zirconia powder (C) can be adjusted within the aforementioned ranges to obtain the tetragonal phase content ratio and the cubic phase content ratio in Embodiments (A-5) and (A-6).

[0360] As the solvent used in wet mixing, there is no particular limitation as long as it contains water. An organic solvent can be used, a mixed solvent of water and an organic solvent can be used, or only water can be used.

[0361] Examples of the organic solvent 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 glycerol; ketones such as acetone and methyl ethyl ketone; ethers (including modified ethers such as propylene glycol monomethyl ether acetate (commonly known as "PGMEA") (preferably ether-modified ethers and / or ester-modified ethers, more preferably ether-modified alkylene glycols and / or ester-modified alkylene glycols)) such as tetrahydrofuran, diethyl ether, diisopropyl ether, 1,4-dioxane, and dimethoxyethane; 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 can be used alone as one kind, or two or more kinds can be used in combination.

[0362] The zirconia composition of the present invention can be in a dry state, or in a state containing a liquid or contained in a liquid. For example, the zirconia composition can take forms such as powder, paste, slurry, etc.

[0363] The method of wet-mixing the above-mentioned respective raw materials in a solvent containing water is not particularly limited. For example, the respective raw materials can be wet-crushed and mixed using a known crushing and mixing device (such as a ball mill) to form a slurry containing zirconia-based particles. Thereafter, the slurry containing zirconia-based particles is dried and granulated to produce a granular zirconia composition.

[0364] Hereinafter, the mixed powder obtained by mixing zirconia powder and stabilizer powder will also be referred to as "powder containing zirconia-based particles".

[0365] In the case of drying and granulating the slurry, the drying method is not particularly limited, and for example, spray drying (spray drying), supercritical drying, freeze drying, hot air drying, vacuum drying, etc. can be adopted. Among them, from the viewpoints of being able to suppress the aggregation of particles during drying and being able to obtain a denser zirconia sintered body, etc., any one of spray drying, supercritical drying, and freeze drying is preferred, any one of spray drying and supercritical drying is more preferred, and spray drying is further preferred.

[0366] The slurry containing zirconia-based particles to be dried can be a slurry with water as the dispersion medium. From the viewpoints of being able to suppress the aggregation of particles during drying and being able to obtain a denser zirconia sintered body, etc., a slurry with a dispersion medium other than water such as an organic solvent is preferred.

[0367] From the viewpoints of being able to suppress the aggregation of particles during drying and being able to obtain a denser zirconia sintered body, etc., the water content in the slurry containing zirconia-based particles to be dried is preferably 3% by mass or less, more preferably 1% by mass or less, and further preferably 0.1% by mass or less. This water content can be measured using a Karl Fischer moisture meter.

[0368] The drying conditions in each drying method are not particularly limited, and known drying conditions can be appropriately adopted. It should be noted that in the case of using an organic solvent as the dispersion medium, in order to reduce the explosion risk during drying, it is preferred to carry out drying in the presence of a non-combustible gas, and more preferably to carry out drying in the presence of nitrogen.

[0369] The supercritical fluid for supercritical drying is not particularly limited, and for example, water, carbon dioxide, etc. can be used. From the viewpoints of being able to suppress the aggregation of particles and being able to obtain a denser zirconia sintered body, etc., the supercritical fluid is preferably carbon dioxide.

[0370] In addition, especially in the case of spray drying, if 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, aggregation of zirconia particles with each other can be suppressed during drying, and a denser zirconia sintered body can be obtained, which is therefore preferred. From this viewpoint, the surface tension of the aforementioned liquid is preferably 40 mN / m or less, more preferably 30 mN / m or less.

[0371] The surface tension at 25°C can be determined using, for example, the values described in the Handbook of Chemistry and Physics. For liquids not described therein, the values described in International Publication No. 2014 / 126034 can be used. For liquids not described in either of them, the surface tension can be determined by a known measurement method, and for example, the ring method, the Wilhelmy method, etc. can be used for measurement. The surface tension at 25°C is preferably measured using an automatic surface tensiometer "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. or "SIGMA702" manufactured by KSV INSTRUMENTS LTD (currently: Biolin Scientific AB (Sweden)).

[0372] As the aforementioned liquid, an organic solvent having the aforementioned surface tension can be used. As the organic solvent, an organic solvent having the aforementioned surface tension among the above organic solvents can be used. From the viewpoint of suppressing aggregation of particles with each other during drying and obtaining a denser zirconia sintered body, etc., it is preferably at least one selected from methanol, ethanol, 2-methoxyethanol, 1,4-dioxane, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol, more preferably at least one selected from methanol, ethanol, 2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol.

[0373] From the viewpoint of suppressing aggregation of particles with each other during drying and obtaining a denser zirconia sintered body, etc., the content rate of the above liquid in the dispersion medium is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 95% by mass or more, and particularly preferably 99% by mass or more.

[0374] A slurry with a dispersion medium other than water is a slurry with water as the dispersion medium, and can be obtained by replacing the dispersion medium. The method for replacing the dispersion medium is not particularly limited. For example, a method can be adopted in which a dispersion medium other than water (such as an organic solvent) is added to a slurry with water as the dispersion medium, and then water is removed by distillation. In the distillation removal of water, a part or all of the dispersion medium other than water can be removed simultaneously by distillation. The addition of the dispersion medium other than water and the distillation removal of water can be repeated multiple times. Additionally, a method can also be adopted in which a dispersion medium other than water is added to a slurry with water as the dispersion medium, and then the dispersed substance is precipitated. Furthermore, for a slurry with water as the dispersion medium, after replacing the dispersion medium with a specific organic solvent, it can be further replaced with other organic solvents.

[0375] It should be noted that the fluorescent agent can be added after replacing the dispersion medium. From the perspective of obtaining a more uniform and excellent physical property zirconia sintered body, etc., it is preferably added before replacing the dispersion medium. Similarly, in the case where the slurry contains a colorant and / or a light transmittance regulator, it can be added after replacing the dispersion medium. From the perspective of obtaining a more uniform and excellent physical property zirconia sintered body, etc., it is preferably added before replacing the dispersion medium.

[0376] On the other hand, as the aggregation process, for example, a gas-phase thermal decomposition method in which an oxygen-containing salt or an organometallic compound of a metal ion with a high vapor pressure is gasified and thermally decomposed to precipitate an oxide; a gas-phase reaction method in which a gas of a metal compound with a high vapor pressure reacts with a reaction gas for synthesis; an evaporation concentration method in which the raw material is heated to gasify it, and it is rapidly cooled in an inert gas at a specified pressure, so that the vapor condenses into fine particles; a melt method in which the melt is cooled and solidified in the form of small droplets to form a powder; a solvent evaporation method in which the solvent is evaporated to increase the concentration in the liquid to make it in a supersaturated state and precipitate it; a precipitation method in which the concentration of the solute is made in a supersaturated state through reaction with a precipitant and hydrolysis, and an oxide, hydroxide, etc. of a poorly soluble compound is precipitated through a nucleation-growth process, etc.

[0377] The precipitation method can be further subdivided into a homogeneous precipitation method in which a precipitant is generated in the solution through a chemical reaction to eliminate local non-uniformity of the precipitant concentration; a coprecipitation method in which a precipitant is added to simultaneously precipitate multiple metal ions coexisting in the liquid; a hydrolysis method in which an oxide or hydroxide is obtained from a metal salt solution, an alcohol solution of a metal alkoxide, etc. through hydrolysis; a solvothermal synthesis method in which an oxide or hydroxide is obtained from a high-temperature and high-pressure fluid, etc. The solvothermal synthesis method is further subdivided into a hydrothermal synthesis method using water as a solvent; a supercritical synthesis method using a supercritical fluid such as water or carbon dioxide as a solvent, etc.

[0378] It should be noted that in the present invention, from the perspective that various particles have the desired average particle sizes (r1) and (r2), the coprecipitation method using zirconia and a stabilizer is preferably not employed for zirconia powder and stabilizer powder.

[0379] As the zirconium source in the aggregation process, for example, nitrates, acetates, chlorides, alkoxides, etc. can be used. Specifically, zirconium oxychloride, zirconium acetate, zirconium oxynitrate, etc. can be cited as the zirconium source.

[0380] When the zirconia powder is manufactured by methods such as the aggregation process, as long as the average particle size of the zirconia particles is within the desired range, it can be used in the slurry form containing zirconia particles without drying treatment for the process of mixing the zirconia powder and the stabilizer powder. The method for preparing the slurry containing the aforementioned zirconia particles is not particularly limited. For example, it can be obtained through the above-mentioned disintegration process and aggregation process.

[0381] When the zirconia composition of the present invention is in a dry state, it can be obtained by drying the slurry containing zirconia particles.

[0382] The zirconia composition of the present invention can be made into a molded body through a molding process.

[0383] The "molded body" refers to an object that has not reached either the semi-sintered state (pre-fired state) or the sintered state. That is, the molded body is distinguished from the pre-fired body and the sintered body in that it has not been calcined after being formed into a molded body by molding.

[0384] The type of this molding process is not particularly limited. From the perspective of being able to easily obtain the zirconia molded body of the present invention, and further the zirconia pre-fired body and zirconia sintered body of the present invention, etc., this molding process is preferably at least any one of the following processes, and more preferably a method having a molding process of molding zirconia-based particles, polyhydric alcohol, and a binder to obtain a zirconia molded body.

[0385] (i) The process of slip casting a slurry containing zirconia-based particles;

[0386] (ii) The process of gel casting a slurry containing zirconia-based particles;

[0387] (iii) The process of pressure molding a powder containing zirconia-based particles;

[0388] (iv) The process of molding a composition containing zirconia-based particles and a resin;

[0389] (v) The process of polymerizing a composition containing zirconia-based particles and a polymerizable monomer and / or oligomer; and

[0390] (vi) A step of laminating and shaping particles containing zirconia-based particles.

[0391] (i) Slip casting

[0392] When manufacturing a zirconia molded body by a method having a step of slip casting a slurry containing zirconia-based particles, the specific method of slip casting is not particularly limited, and for example, a method of flowing a slurry containing zirconia-based particles into a mold and then drying it can be adopted.

[0393] From the viewpoints of facilitating the flow of the slurry into the mold, preventing excessive drying time, and increasing the number of uses of the mold, the content rate of the dispersion medium in the slurry containing zirconia-based particles used is preferably 80% by mass or less, more preferably 50% by mass or less, and further preferably 20% by mass or less.

[0394] The flow of the slurry into the mold can be carried out under normal pressure, and from the viewpoint of production efficiency, it is preferably carried out under pressure conditions. The type of mold used in slip casting is not particularly limited, and for example, a porous mold formed of gypsum, resin, ceramic, etc. can be used. Porous molds formed of resin or ceramic are excellent in terms of durability.

[0395] The slurry containing zirconia-based particles used in slip casting may further contain one or more of other components such as the above-mentioned binder, plasticizer, dispersant, emulsifier, defoamer, pH regulator, lubricant, etc.

[0396] (ii) Gel casting

[0397] When manufacturing a zirconia molded body by a method having a step of gel casting a slurry containing zirconia-based particles, the specific method of gel casting is not particularly limited, and for example, a method of gelating a slurry containing zirconia particles and a fluorescent agent in a mold, etc., obtaining a shaped wet body, and then drying it can be adopted.

[0398] From the viewpoints of preventing excessive drying time and suppressing the generation of cracks during drying, the content rate of the dispersion medium in the slurry containing zirconia-based particles used is preferably 80% by mass or less, more preferably 50% by mass or less, and further preferably 20% by mass or less.

[0399] The above gelation can be carried out by, for example, adding a gelling agent, or by polymerizing a polymerizable monomer after adding it. The type of mold used is not particularly limited, and for example, a porous mold formed of gypsum, resin, ceramic, etc. can be used; a non-porous mold formed of metal, resin, etc. can also be used.

[0400] The type of the gelling agent is not limited, and a water-soluble gelling agent can be used, for example. Specifically, agarose, gelatin, etc. can be preferably used. The gelling agent can be used alone as one kind, or two or more kinds can be used in combination. The amount of the gelling agent is not particularly limited as long as there are no problems such as cracks during sintering. According to the mass of the slurry after compounding the gelling agent, it can be set to 10% by mass or less, can be set to 5% by mass or less, or can also be set to 1% by mass or less.

[0401] In addition, the type of the 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, erythritol mono(meth)acrylate; (meth)acrylamide monomers such as N-hydroxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, N,N-bis(2-hydroxyethyl)(meth)acrylamide, etc.

[0402] The polymerizable monomer can be used alone as one kind, or two or more kinds can be used in combination.

[0403] The amount of the polymerizable monomer is not particularly limited as long as there are no problems such as cracks during sintering. According to the mass of the slurry after compounding the polymerizable monomer, it can be set to 10% by mass or less, can be set to 5% by mass or less, or can also be set to 1% by mass or less.

[0404] When gelation is carried out by polymerization of the polymerizable monomer, the polymerization is preferably carried out using a polymerization initiator. The type of the polymerization initiator is not particularly limited, and a photoinitiator is particularly preferred. As the photoinitiator, it can be appropriately selected from the photoinitiators commonly used in the industry, and among them, the photoinitiator used in dental applications is preferred.

[0405] As specific photoinitiators, examples include (bis)acylphosphine oxides (including salts), thioxanthones (including salts such as quaternary ammonium salts), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ether compounds, α-aminoketone compounds, etc. The photoinitiator can be used alone as one kind, or two or more kinds can be used in combination. Among these photoinitiators, at least one selected from (bis)acylphosphine oxides and α-diketones is preferably used. Thereby, polymerization (gelation) can be carried out in both the ultraviolet region (including the near-ultraviolet region) and the visible light region. In particular, even when using any light source such as Ar laser, He-Cd laser, etc.; halogen lamp, xenon lamp, metal halide lamp, light-emitting diode (LED), mercury lamp, fluorescent lamp, etc., polymerization (gelation) can be sufficiently carried out.

[0406] Among the above-mentioned (bis)acylphosphine oxides, examples of acylphosphine oxides include 2,4,6-trimethylbenzoyl diphenylphosphine oxide (commonly known as "TPO"), 2,6-dimethoxybenzoyl diphenylphosphine oxide, 2,6-dichlorobenzoyl diphenylphosphine oxide, 2,4,6-trimethylbenzoyl methoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyl ethoxyphenylphosphine oxide, 2,3,5,6-tetramethylbenzoyl diphenylphosphine oxide, benzoyl bis(2,6-dimethylphenyl)phosphate, sodium salt of 2,4,6-trimethylbenzoyl phenylphosphine oxide, potassium salt of 2,4,6-trimethylbenzoyl diphenylphosphine oxide, ammonium salt of 2,4,6-trimethylbenzoyl diphenylphosphine oxide, and the like.

[0407] Among the above-mentioned (bis)acylphosphine oxides, examples of 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, bis(2,3,6-trimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, and the like. Further, compounds described in JP-A-2000-159621 can also be used.

[0408] Among these (bis)acylphosphine oxides, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, 2,4,6-trimethylbenzoyl methoxyphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and sodium salt of 2,4,6-trimethylbenzoyl phenylphosphine oxide are preferred.

[0409] Examples of α-diketones include diacetyl, benzil, camphorquinone, 2,3-pentanedione, 2,3-octanedione, 9,10-phenanthrenequinone, 4,4'-oxybisbenzil, acenaphthenequinone, and the like. Among these, camphorquinone is particularly preferred, for example, when using a light source in the visible light region.

[0410] Regarding the above-mentioned slurry containing zirconia-based particles used in gel casting, similar to the slurry used in slip casting, it can 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, a lubricant, and the like.

[0411] The drying method when 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, constant temperature and humidity drying, etc. They can be used alone or in combination of two or more. Among these, from the perspective of being able to suppress the generation of cracks during drying, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred.

[0412] (iii) Press molding

[0413] When manufacturing a zirconia molded body by a method having a step of press molding a powder containing zirconia-based particles, the specific method of press molding is not particularly limited, and a known press molding machine can be used.

[0414] As the specific method of press molding, examples include uniaxial pressing, etc.

[0415] The pressing pressure in press molding is appropriately set to an optimal value according to the size, open porosity, biaxial flexural strength, and particle diameter of the raw material powder of the target molded body, and is usually 5 MPa or more and 1000 MPa or less. By increasing the pressing pressure during molding in the above manufacturing method, the pores of the obtained molded body can be further filled, the open porosity can be set low, and the density of the molded body can be increased. In addition, in order to increase the density of the obtained zirconia molded body, cold isostatic pressing (CIP) treatment can be further performed after uniaxial pressing.

[0416] The above powder containing zirconia-based particles used in press molding 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 regulator, a lubricant, and a light transmittance regulator. These components can be compounded during the preparation of the powder.

[0417] (iv) Molding of a resin-containing composition

[0418] When manufacturing a zirconia molded body by a method having 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, injection molding, extrusion molding, etc. can be adopted. In addition, a method of shaping the composition by a thermal dissolution method (FDM), an inkjet method, a powder / binder lamination method, etc., a lamination shaping method (3D printing, etc.) can be adopted. Among these molding methods, injection molding and injection molding are preferred, and injection molding is more preferred.

[0419] There is no particular limitation on the type of the above resin, and a resin that functions as a binder is preferably used. Specific examples of the resin include, for example, paraffin, polyvinyl alcohol, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polystyrene, atactic polypropylene, methacrylic resin, fatty acids such as stearic acid, etc. These resins can be used alone or in combination of two or more.

[0420] The above composition containing zirconia-based particles and a resin 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, a lubricant, etc.

[0421] (v) Polymerization of a composition containing a polymerizable monomer and / or an oligomer

[0422] By polymerizing a composition containing zirconia-based particles and a polymerizable monomer and / or an oligomer, the polymerizable monomer in the composition polymerizes, enabling the composition to be cured.

[0423] When manufacturing a zirconia molded body by a method having this polymerization step, the specific method is not particularly limited, and for example, (a) a method of polymerizing a composition containing zirconia-based particles and a polymerizable monomer and / or an oligomer in a mold; (b) a stereolithography (SLA) method using a composition containing zirconia-based particles and a polymerizable monomer and / or an oligomer, etc. Among these, the stereolithography method of (b) is preferred.

[0424] According to the stereolithography method, it is possible to impart a shape corresponding to the desired shape of the finally obtained zirconia sintered body at the time of manufacturing the zirconia molded body. Therefore, especially when using the zirconia sintered body of the present invention as a dental material such as a dental prosthesis, etc., the stereolithography method is sometimes suitable.

[0425] The type of the polymerizable monomer in the above composition containing zirconia-based particles and a polymerizable monomer and / or an oligomer is not particularly limited, and it can be any of monofunctional (meth)acrylate, monofunctional (meth)acrylamide and other monofunctional polymerizable monomers, and polyfunctional polymerizable monomers such as difunctional aromatic compounds, difunctional aliphatic compounds, compounds having trifunctionality or more. The polymerizable monomer can be used alone or in combination of two or more.

[0426] The oligomer is not particularly limited as long as it is a compound in which two or more of the above polymerizable monomers are bonded and has polymerizability.

[0427] Among these, especially when using the stereolithography method, etc., a polyfunctional polymerizable monomer is preferably used.

[0428] Examples of the monofunctional (meth)acrylate include (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, erythritol mono(meth)acrylate; (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate; alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate; (meth)acrylates containing an aromatic group such as benzyl (meth)acrylate, phenyl (meth)acrylate; (meth)acrylates having a functional group such as 2,3-dibromopropyl (meth)acrylate, 3-(meth)acryloxypropyltrimethoxysilane, 11-(meth)acryloxyundecyltrimethoxysilane, etc.

[0429] Examples of the monofunctional (meth)acrylamide 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, N,N-bis(2-hydroxyethyl)(meth)acrylamide, etc.

[0430] Among these monofunctional polymerizable monomers, from the viewpoint of excellent polymerizability, (meth)acrylamide is preferred, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide are more preferred.

[0431] Examples of the bifunctional aromatic compound include 2,2-bis((meth)acryloxyphenyl)propane, 2,2-bis[4-(2-hydroxy-3-acryloxypropoxy)phenyl]propane, 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (commonly known as "Bis-GMA"), 2,2-bis(4-(meth)acryloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxytetraethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxypentaethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxydipropoxyphenyl)propane, 2-(4-(meth)acryloxydiethoxyphenyl)-2-(4-(meth)acryloxyethoxyphenyl)propane, 2-(4-(meth)acryloxydiethoxyphenyl)-2-(4-(meth)acryloxytriethoxyphenyl)propane, 2-(4-(meth)acryloxydipropoxyphenyl)-2-(4-(meth)acryloxytriethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloxyisopropoxyphenyl)propane, 1,4-bis(2-(meth)acryloxyethyl) pyromellitate, and the like (meth)acrylates. Among these, from the viewpoints of excellent polymerizability and mechanical strength of the obtained zirconia molded body, Bis-GMA and 2,2-bis(4-(meth)acryloxypolyethoxyphenyl)propane are preferred. Among 2,2-bis(4-(meth)acryloxypolyethoxyphenyl)propane, 2,2-bis(4-methacryloxypolyethoxyphenyl)propane (average addition mole number of ethoxy group: 2.6, commonly known as "D-2.6E") is preferred.

[0432] Examples of the bifunctional aliphatic compound include glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 2-ethyl-1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,2-bis(3-methacryloyloxy-2-hydroxypropoxy)ethane, 2,2,4-trimethylhexamethylene bis(2-carbamoyloxyethyl) dimethacrylate (commonly known as "UDMA"), and other (meth)acrylates. Among these, from the viewpoint of excellent polymerizability and mechanical strength of the obtained zirconia molded body, triethylene glycol dimethacrylate (commonly known as "TEGDMA") and 2,2,4-trimethylhexamethylene bis(2-carbamoyloxyethyl) dimethacrylate are preferred.

[0433] Examples of the compound having trifunctionality or more include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, N,N-(2,2,4-trimethylhexamethylene) bis[2-(aminocarboxy)propane-1,3-diol] tetra(meth)acrylate, 1,7-diacryloyloxy-2,2,6,6-tetra(meth)acryloxymethyl-4-oxaheptane, and other (meth)acrylates. Among these, from the viewpoint of excellent polymerizability and mechanical strength of the obtained zirconia molded body, N,N-(2,2,4-trimethylhexamethylene) bis[2-(aminocarboxy)propane-1,3-diol] tetramethacrylate and 1,7-diacryloyloxy-2,2,6,6-tetraacryloxymethyl-4-oxaheptane are preferred.

[0434] In any 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. The type of the polymerization initiator is not particularly limited, and a photoinitiator is particularly preferred. As the photoinitiator, it can be appropriately selected from the photoinitiators commonly used in the industry, and among them, the photoinitiator used in dental applications is preferred. Specific examples of the photoinitiator are the same as those described above for the description of gel casting, and repeated description is omitted here.

[0435] The above composition containing zirconia-based particles and a polymerizable monomer may further contain one or more of other components such as a plasticizer, a dispersant, an emulsifier, an antifoaming agent, a pH adjuster, a lubricant, etc. as described above.

[0436] When manufacturing a zirconia molded body by a stereolithography method using a composition containing zirconia-based particles and a polymerizable monomer, the specific method of the stereolithography method is not particularly limited, and a known method can be appropriately adopted for stereolithography. For example, the following methods can be adopted: a method of obtaining a target zirconia molded body by using a stereolithography apparatus to photopolymerize a liquid composition with ultraviolet rays, lasers, etc. to sequentially form each layer having a desired shape.

[0437] When obtaining a zirconia molded body by a stereolithography method, from the viewpoint of sinterability described later, etc., the content rate of the zirconia-based particles in the composition containing zirconia-based particles and a polymerizable monomer is preferably as large as possible. Specifically, the content rate of the zirconia particles in the composition is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and particularly preferably 50% by mass or more. On the other hand, in the stereolithography method, based on the principle of its layer-by-layer molding, the viscosity of the composition is preferably within a certain specified range. Therefore, the content rate of the zirconia-based particles in the above composition is preferably 90% by mass or less, more preferably 80% by mass or less, further preferably 70% by mass or less, and particularly preferably 60% by mass or less. When implementing the restricted liquid surface method of forming a zirconia molded body layer by layer by irradiating light through the bottom surface of the container from below the container to cure the layer, the adjustment of the viscosity of the composition is sometimes particularly important for causing the cured layer to rise only by the amount of one layer and smoothly flowing the composition for forming the next layer between the lower surface of the cured layer and the bottom surface of the container.

[0438] As the specific viscosity of the above composition, using a viscometer at 25°C, it is preferably 20,000 mPa·s or less, more preferably 10,000 mPa·s or less, and further preferably 5,000 mPa·s or less. In addition, as the viscosity, it is preferably 100 mPa·s or more. The composition has a tendency that the higher the content rate of the zirconia particles, the higher the viscosity will be. Therefore, it is preferable to appropriately adjust the balance between the content rate of the zirconia particles and the viscosity in the above composition while considering the balance between the speed during stereolithography and the accuracy of the obtained zirconia molded body, etc., according to the performance of the stereolithography apparatus used, etc. It should be noted that this viscosity can be measured using an E mold viscometer.

[0439] In the method for manufacturing a zirconia molded body of the present invention, in order to further increase the density of the zirconia molded body, a CIP treatment can be performed after performing a humidification treatment on the zirconia molded body.

[0440] In the case of pressure molding, after subjecting the powder containing zirconia particles before pressure molding to a humidification treatment, pressure molding can be performed. As the method of the humidification treatment, a known method can be used without any limitation, and water can be sprayed using a sprayer or the like, or treatment can be performed using a humidifier or a thermo-hygrostat. The amount of moisture increase based on the humidification treatment also depends on the particle size of the contained zirconia particles, the particle size of the stabilizer particles, etc. With respect to the mass of the powder before wetting (powder before humidification treatment) and the molded body, it is preferably more than 2% by mass, more preferably more than 3% by mass, further preferably more than 4% by mass, particularly preferably more than 5% by mass. In addition, it is preferably 15% by mass or less, more preferably 13% by mass or less, and further preferably 11% by mass or less. It should be noted that the amount of moisture increase based on the humidification treatment can be obtained as a percentage by dividing the value obtained by subtracting the mass of the powder before wetting and the molded body from the mass of the wet powder (powder after humidification treatment) and the molded body by the mass of the powder before wetting and the molded body.

[0441] The pressure of the CIP treatment is the same as that described above for the description of pressure molding.

[0442] (vi) Step of laminating and shaping particles containing zirconia-based particles

[0443] In the case of manufacturing particles containing zirconia-based particles, the specific method is not particularly limited. For example, a method of drying the obtained slurry using a spray dryer to form particles can be adopted, and the obtained particles can be used for powder lamination shaping.

[0444] As the method of powder lamination shaping, there is no particular limitation, and 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, a binder jet method, etc. Regarding a method in which it is better not to contain an organic substance during lamination shaping, it is preferable not to use an organic substance also in the manufacturing stage of the particles.

[0445] [Zirconia sintered body]

[0446] Next, the zirconia sintered body of the present invention will be described. The zirconia sintered body of the present invention can be manufactured using a zirconia pre-sintered body. Specifically, the zirconia sintered body of the present invention is obtained by sintering, for example, the aforementioned zirconia pre-sintered body.

[0447] In the zirconia sintered body, zirconia particles are consolidated with each other by sintering. As sintering progresses, the relative density increases and densification occurs, presenting a fully sintered state with a relative density of 95% or more.

[0448] The content rate of the stabilizer in the zirconia sintered body of the present invention is the same as that in the pre-sintered zirconia body.

[0449] The first light transmittance ΔL 1 *(W - B) of the zirconia sintered body produced by sintering the zirconia sintered body of the present invention at 1550°C for 120 minutes and the second light transmittance ΔL 2 *(W - B) of the zirconia sintered body produced by sintering at 1550°C for 10 minutes satisfy the above formula (1) when compared.

[0450] Therefore, after short-time sintering for 10 minutes or less at the highest sintering temperature, the zirconia sintered body of the present invention can maintain a high light transmittance comparable to that of long-time sintering.

[0451] 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 pre-sintered zirconia body. The zirconia sintered body of the present invention may contain one of them alone or may contain two or more in combination.

[0452] In this specification, regarding the fluorescent agent, “relative to 100% by mass of zirconia contained in the pre-sintered zirconia body” can be understood as “relative to 100% by mass of zirconia contained in the zirconia sintered body”.

[0453] The zirconia sintered body of the present invention may contain a colorant. Examples of the colorant include the same colorants as those in the pre-sintered zirconia body.

[0454] The content rate of the colorant in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of the colorant, the use of the zirconia sintered body, etc. From the viewpoint of being preferably used as a dental prosthesis, etc., relative to 100% by mass of zirconia contained in the zirconia sintered body, in terms of the oxide of the metal element contained in the colorant, it is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and further preferably 0.01% by mass or more. In addition, the content rate of the colorant, in terms of the oxide of the metal element contained in the colorant, is preferably 5% by mass or less, more preferably 1% by mass or less, and further preferably 0.5% by mass or less, and can be 0.1% by mass or less, and further can be 0.05% by mass or less.

[0455] In order to adjust the light transmittance of the zirconia sintered body of the present invention, the zirconia sintered body of the present invention may contain a light transmittance regulator. Examples of the light transmittance regulator include the same substances as those in the pre-sintered zirconia body.

[0456] The content rate of the light transmittance regulator in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of the light transmittance regulator, the use of the zirconia sintered body, etc. From the viewpoint of being preferably used as dental prostheses, etc., it is preferably 0.1% by mass or less relative to 100% by mass of zirconia contained in the zirconia sintered body.

[0457] [Manufacturing method of zirconia sintered body]

[0458] As the manufacturing method of the zirconia sintered body of the present invention, a manufacturing method of a zirconia sintered body can be cited, in which the aforementioned zirconia pre-sintered body is sintered. A manufacturing method preferably including a step of sintering the aforementioned zirconia pre-sintered body under normal pressure at a temperature exceeding 900°C and being 1700°C or less can be cited. By this manufacturing method, it is possible to easily manufacture the zirconia sintered body of the present invention that can maintain the same degree of high light transmittance as that of long-time sintering after short-time sintering with a holding time of 10 minutes or less at the highest sintering temperature.

[0459] The zirconia sintered body of the present invention can also be manufactured by sintering the zirconia pre-sintered body of the present invention under normal pressure.

[0460] When manufacturing a sintered body by sintering the zirconia pre-sintered body of the present invention, the sintering temperature (for example, the highest sintering temperature) is preferably a condition under which the light transmittance of the zirconia sintered body reaches the maximum.

[0461] From the viewpoint of easily obtaining the target zirconia sintered body under normal pressure, etc., the sintering temperature is preferably exceeding 900°C, more preferably 1000°C or higher, further preferably 1050°C or higher. In addition, it is preferably 1700°C or lower, more preferably 1650°C or lower, and further preferably lower than 1600°C.

[0462] In a certain preferred embodiment, from the viewpoint that the light transmittance is excellent even at a lower sintering temperature during short-time sintering, a manufacturing method of a zirconia sintered body can be cited, in which the zirconia pre-sintered body is sintered under normal pressure at a temperature exceeding 900°C and being 1560°C or less. Compared with the prior art, the light transmittance is excellent during short-time sintering at a sintering temperature based on a lower temperature, and thus it is industrially advantageous.

[0463] By making the sintering temperature be above the above lower limit and making the sintering temperature be below the above upper limit, sintering can be sufficiently performed, and a dense sintered body can be easily obtained. In addition, by making the sintering temperature be below the above upper limit, inactivation of the fluorescent agent can be suppressed.

[0464] In the case of manufacturing a sintered body, as long as the holding time at the highest sintering temperature is 10 minutes or less, the sintering time is not particularly limited. Starting from the ability to effectively and stably obtain a target zirconia sintered body or the like with good productivity, the holding time at the sintering temperature (e.g., the highest sintering temperature) is preferably 10 minutes or less, more preferably 9 minutes or less, further preferably 8 minutes or less, still further preferably 7 minutes or less, particularly preferably 6 minutes or less, and most preferably 5 minutes or less. This holding time is preferably 1 minute or more, more preferably 2 minutes or more, and further preferably 3 minutes or more.

[0465] In the case of manufacturing a sintered body, it is possible to shorten the sintering time for manufacturing the sintered body without reducing the translucency of the produced zirconia sintered body. In particular, the holding time at the highest sintering temperature for manufacturing the sintered body can be shortened to 10 minutes or less. Thereby, the production efficiency can be improved. When the zirconia pre-sintered body of the present invention is applied to dental products, the dimensions of the dental products used in treatment can be determined, the time from cutting to being able to use the dental products for treatment can be shortened, and the time burden on patients can be reduced. In addition, the energy cost can be reduced.

[0466] The heating rate and cooling rate in the sintering process are preferably set in such a way that the time required for the sintering process is shortened. For example, the heating rate can be set according to the performance of the calcining furnace to reach the highest sintering temperature in the shortest time. The heating rate up to the highest sintering temperature can be set, for example, to 10 °C / min or more, 50 °C / min or more, 100 °C / min or more, 120 °C / min or more, 150 °C / min or more, or 200 °C / min or more. The cooling rate is preferably set to a rate such that no defects such as cracks occur in the sintered body. For example, after the heating is completed, the sintered body can be naturally cooled at room temperature.

[0467] The sintering in the present invention can be carried out using a sintering furnace. The type of the sintering furnace is not particularly limited, and for example, an electric furnace and a debinding furnace commonly used in the industry can be used. Especially when used in the field of dental materials, in addition to the conventional sintering furnace for dental zirconia, a dental ceramic furnace with a lower sintering temperature (e.g., the highest sintering temperature) can also be used.

[0468] The zirconia sintered body of the present invention can be easily manufactured even without HIP treatment, but by performing HIP treatment after the above-mentioned sintering under normal pressure, the translucency and mechanical strength can be further improved.

[0469] 〔Use of zirconia sintered body〕

[0470] The use of the zirconia sintered body of the present invention is not particularly limited.

[0471] The zirconia sintered body of the present invention is particularly suitable as a dental material such as a dental prosthesis due to its excellent light transmittance and excellent linear light transmittance. Among them, it is extremely useful not only as a dental prosthesis used at the tooth neck, but also as a dental prosthesis used at the molar occlusal surface and the incisor cutting end.

[0472] The zirconia sintered body of the present invention is extremely useful especially as a dental prosthesis used at the incisor cutting end.

[0473] As long as the effects of the present invention are exhibited, the present invention includes embodiments in which the above-described configurations are variously combined within the technical idea of the present invention.

[0474] Examples

[0475] Next, examples are listed to more specifically illustrate the present invention. However, the present invention is not limited to these examples at all, and those with common general knowledge in the art can make various modifications within the technical idea of the present invention.

[0476] [Raw material powder]

[0477] Monoclinic 0Y: zirconia powder ("TZ-0" manufactured by Tosoh Corporation)

[0478] Tetragonal 3Y: zirconia powder in which 3 mol% of yttrium oxide is dissolved ("TZ-3Y-E" manufactured by Tosoh Corporation)

[0479] Cubic 6Y: zirconia powder in which 6 mol% of yttrium oxide is dissolved ("TZ-6Y" manufactured by Tosoh Corporation)

[0480] Cubic 10Y: zirconia powder in which 10 mol% of yttrium oxide is dissolved ("TZ-10Y" manufactured by Tosoh Corporation)

[0481] Cubic 15Y: After mixing and drying a zirconia sol obtained by hydrolyzing an aqueous zirconium oxychloride solution with yttrium oxide, the obtained powder is heat-treated in the atmosphere at 1160 °C for 2 hours to obtain a yttrium-containing zirconia powder with a yttrium oxide content of 15 mol%.

[0482] Yttrium oxide: yttrium oxide powder (Y manufactured by Treibacher Industrie AG) 2 O 3 )

[0483] [Examples 1 to 15 and Comparative Examples 1 to 6]

[0484] [Preparation of zirconia compositions of Examples 1 to 15 and Comparative Examples 1 to 3]

[0485] To prepare the granular raw material compositions of each of the examples and comparative examples, the above raw material powders were mixed so as to have the compositions described in Table 1, water was added, and wet pulverization and mixing were performed using a ball mill for 20 hours. After adding a binder to the pulverized slurry, it was dried using a spray dryer to obtain a granular zirconia composition.

[0486] It should be noted that in Table 1 and Table 2 below, the "total yttrium oxide amount" represents the content rate of yttrium oxide relative to the total moles of zirconia and yttrium oxide.

[0487] [Preparation of zirconia compositions of Comparative Examples 4 and 5]

[0488] The above raw material powders were mixed so as to have the compositions described in Table 1, water was added, and wet pulverization and mixing were performed using a ball mill for 20 hours. After adding a binder to the pulverized slurry, it was dried using a spray dryer to obtain granules. The granules were heated to 1000 °C at a rate of 10 °C / minute and held for 2 hours, then water was added, and wet pulverization and mixing were performed using a ball mill for 20 hours. After adding a binder to the pulverized slurry, it was dried using a spray dryer to obtain a granular zirconia composition.

[0489] [Preparation of zirconia composition of Comparative Example 6]

[0490] The above monoclinic 0Y powder and tetragonal 3Y powder were mixed so as to have the compositions described in Table 1, water was added, and wet pulverization and mixing were performed using a ball mill for 15 hours to obtain a slurry.

[0491] Yttrium oxide powder was mixed into the slurry so as to have the compositions described in Table 1, water was added, and further wet pulverization and mixing were performed using a ball mill for 5 hours. After adding a binder to the pulverized slurry, it was dried using a spray dryer to obtain a granular zirconia composition.

[0492] [Preparation of zirconia pre-sintered body]

[0493] For each of the examples and comparative examples, in order to obtain samples of zirconia sintered bodies for light transmittance evaluation, pre-sintered bodies in the form of pellets were prepared as follows.

[0494] First, a cylindrical mold with a diameter of 19 mm was used, and the aforementioned raw material composition was put into the mold in such a way that the thickness of the processed zirconia composite sintered body after sintering became 1.2 mm. Then, using a uniaxial pressing machine, the raw material composition was press-molded with a surface pressure of 200 MPa to produce a pellet-shaped green body. Using a calcination furnace "Noritake KATANA (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd., the obtained pellet-shaped green body was heated to 1000 °C at a rate of 10 °C / min and held for 2 hours, and then cooled to obtain a zirconia pre-sintered body.

[0495] [Fabrication of Zirconia Sintered Body]

[0496] Regarding the obtained pellet-shaped pre-sintered body, using a calcination furnace "Noritake KATANA (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd., the ΔL of the first sintered body fabricated by sintering at 1550 °C for 120 minutes was obtained. 1 *ΔL of the specimen for measuring (W-B) and the second sintered body fabricated by sintering at 1550 °C for 10 minutes 2 *Specimen for measuring (W-B).

[0497] For the zirconia sintered bodies manufactured in each example and comparative example, the following methods were used to measure each property.

[0498] <Method for Measuring the Average Primary Particle Size of Particles in Zirconia Composition>

[0499] Regarding various particles (zirconia particles, yttrium oxide particles) in the zirconia composition, using each raw material powder, for the primary particles constituting the particles obtained by the above method for fabricating the zirconia composition, the average primary particle size was measured using the following method.

[0500] For the obtained particulate powder, a surface image (SEM image) was obtained using a scanning electron microscope (trade name "VE-9800", manufactured by Keyence Corporation). After recording the grain boundaries of each particle in the obtained image, the average primary particle size was calculated by image analysis.

[0501] The particle size was measured using image analysis software (trade name "Image-Pro Plus ver.7.0.1", manufactured by Pearton Corporation). The read SEM image was binarized, the brightness range was adjusted so that the grain boundaries were clear, and the particles were identified according to the field of view (area).

[0502] The particle size obtained using Image-Pro Plus refers to the diameter passing through the center of gravity of the particle. The diameter passing through the center of gravity of the particle means: centered on the center of gravity, the length of the line segment connecting the contour lines passing through the center of gravity obtained from the contour line of the particle is measured at a scale of 2 degrees, and the measured values (180 values) are averaged to obtain the diameter.

[0503] In the measurement of particle size, particles not involving the image edges are used as the measurement objects. "Particles not involving the image edges" refer to: in the SEM photo image, particles after removing the particles whose contour lines do not completely fall within (particles whose contour lines are cut off on the upper, lower, left, and right boundary lines). The particle sizes of all particles not involving the image edges are selected through the option of removing all particles on the boundary lines in Image-Pro Plus.

[0504] For one sample in each of the examples and comparative examples, the particle sizes of each particle in 3 fields of view are obtained, and the average primary particle size is calculated.

[0505] <Content ratio (mol%) of stabilizer in zirconia composition and zirconia pre-sintered body>

[0506] The content ratio (mol%) of the stabilizer in the zirconia composition and zirconia pre-sintered body is calculated based on the content ratio of the stabilizer relative to the total moles of zirconia and the stabilizer, and is measured using a fluorescence X-ray analysis (XRF) device (RX3000, manufactured by Matsusada Precision Co., Ltd.).

[0507] <Evaluation of crystal phase ratio of zirconia pre-sintered body>

[0508] Tetragonal phase ratio f of zirconia pre-sintered body t 、Cubic phase ratio f c And monoclinic phase ratio f m Are obtained through the analysis of the crystal phases in the zirconia pre-sintered body.

[0509] Specifically, for the X-ray diffraction measurement, a fully automatic horizontal multi-purpose X-ray diffraction device (SmartLab, manufactured by Rigaku Corporation) and X-ray analysis integrated software (SmartLab StudioII, manufactured by Rigaku Corporation) are used, and the measurement is carried out under the following conditions to obtain the area intensity of each peak (peak area intensity I).

[0510] X-ray source: Cu Kα

[0511] Goniometer length: 300 mm

[0512] Optical system: Convergent method

[0513] Detector: High-speed one-dimensional X-ray detector (D / teX Ultra 250)

[0514] Monochromatization: Kβ filter

[0515] Tube voltage: 40 kV

[0516] Tube current: 30 mA

[0517] Scanning axis: 2θ / θ

[0518] Scanning speed: 0.2° / min

[0519] Sampling step: 0.01°

[0520] Regarding the crystal phase ratio, each peak is attributed to a crystal phase, and the calculation is performed according to the following formulas (2-1), (2-2), and (2-3) respectively.

[0521] Tetragonal crystal ratio f t (%) = I t / (I m + I t + I c + I y ) × 100 (2-1)

[0522] Cubic crystal ratio f c (%) = I c / (I m + I t + I c + I y ) × 100 (2-2)

[0523] Monoclinic crystal ratio f m (%) = I m / (I m + I t + I c + I y ) × 100 (2-3)

[0524] (In the formula, f m represents the monoclinic crystal ratio (%), f t represents the tetragonal crystal ratio (%), f c represents the cubic crystal ratio (%). In XRD measurement, I m represents the area intensity of the peak near 2θ = 28.2° at the peak top of the main peak of the monoclinic crystal system, I t represents the area intensity of the peak near 2θ = 30.2° at the peak top of the main peak of the tetragonal crystal system, I c represents the area intensity of the peak near 2θ = 30.1° at the peak top of the main peak of the cubic crystal system, I yIndicates the area intensity of the peak near 2θ = 29.2° at the peak top of the main peak where yttrium oxide is not dissolved.)

[0525] During the measurement, the disc-shaped zirconia pre-sintered bodies of each example and comparative example were used as samples.)

[0526] <Determination of the ratio of yttrium oxide not dissolved in zirconia in the zirconia pre-sintered body>

[0527] Regarding the content rate f of yttrium oxide not dissolved in the zirconia pre-sintered body y , X-ray diffraction (XRD) measurement based on CuKα rays was carried out and calculated according to the following formula (2-4).

[0528] f y (%) = I y / (I m + I t + I c + I y ) × 100 (2-4)

[0529] (In the formula, f y represents the ratio (%) of yttrium oxide not dissolved. In the XRD measurement, I m represents the area intensity of the peak near 2θ = 28.2° at the peak top of the main peak of the monoclinic system, I t represents the area intensity of the peak near 2θ = 30.2° at the peak top of the main peak of the tetragonal system, I c represents the area intensity of the peak near 2θ = 30.1° at the peak top of the main peak of the cubic system, I y represents the area intensity of the peak near 2θ = 29.2° at the peak top of the main peak where yttrium oxide is not dissolved.)

[0530] <Determination of the standard deviation of the yttrium element distribution in the zirconia pre-sintered body>

[0531] Regarding the yttrium element distribution of the zirconia pre-sintered body, a field emission scanning electron microscope (FE-SEM Reglus8220, manufactured by Hitachi High-Tech Corporation) and an energy dispersive X-ray analysis device (Aztec Energy X-Max50, manufactured by Oxford Instruments) were used, and the measurement was carried out under the following conditions. The yttrium element was observed using 1.923 keV.)

[0532] The standard deviation (mol%) of the yttrium element of 10 particles derived from the stabilizer was calculated.)

[0533] Magnification for measurement: 20,000 times

[0534] Analysis mode: Point analysis

[0535] Accelerating voltage: 5 kV

[0536] Working distance: 15 mm ± 1 mm

[0537] X-ray extraction angle: 30 degrees

[0538] No-load time: 7%

[0539] Measurement time: 100 seconds

[0540] <Method for measuring the average primary particle size of particles in a zirconia pre-sintered body>

[0541] For the zirconia pre-sintered body obtained in the examples or comparative examples, a surface photograph (SEM image) was obtained using a scanning electron microscope (trade name “VE-9800”, manufactured by Keyence Corporation). After recording the grain boundaries of each crystal particle in the obtained image, the primary particle size of each crystal particle was measured using image analysis.

[0542] For the measurement of the particle size, an image analysis software (trade name “Image-Pro Plus ver.7.0.1”, manufactured by Pei Dong Corporation) was used. The read SEM image was binarized, the brightness range was adjusted so that the grain boundaries were clear, and the particles were identified according to the field of view (area).

[0543] The particle size obtained using Image-Pro Plus refers to the diameter passing through the center of gravity of the particle. The diameter passing through the center of gravity of the particle means: centered on the center of gravity, the length of the line segment connecting the outer contour lines passing through the center of gravity obtained from the outer contour line of the particle is measured at a scale of 2 degrees, and the measured values (180) are averaged to obtain the diameter.

[0544] In the measurement of the particle size, the particles not related to the image end are used as the measurement object. “Particles not related to the image end” means: in the SEM photograph image, the particles after removing the particles whose outer contour lines do not all fall within (the particles whose outer contour lines are cut off on the upper, lower, left, and right boundary lines). The particle sizes of all particles not related to the image end are selected through the option of removing all particles on the boundary lines in Image-Pro Plus.

[0545] For one sample in each of the examples and comparative examples, the particle sizes of each crystal particle in 3 fields of view were obtained, and the average primary particle size was calculated.

[0546] <Evaluation of the light transmittance of a zirconia sintered body (measurement of ΔL*(W - B))>

[0547] The maximum sintering temperature was set to 1550 °C, and the holding time at this maximum sintering temperature was set to 120 minutes (120-minute sintering). The green compacts obtained in the examples and comparative examples were calcined to produce zirconia sintered bodies (first sintered bodies).

[0548] Next, for the green compacts produced by the same method, the maximum sintering temperature was set to 1550 °C, and the holding time at this maximum sintering temperature was set to 10 minutes (10-minute sintering), followed by calcination to produce zirconia sintered bodies (second sintered bodies).

[0549] Regarding the heating rate and cooling rate, they were set the same for both the 10-minute sintering and the 120-minute sintering.

[0550] The two obtained zirconia sintered bodies were each ground into flat specimens with a thickness of 1.20 mm as specimens for measuring light transmittance. The light transmittance of this specimen was measured using a spectrophotometer (trade name “Crystaleye”) manufactured by Olympus Corporation, and the measurement was carried out using the measurement mode: 7band LED light source.

[0551] Specifically, regarding the light transmittance of the zirconia sintered body as a flat specimen, the brightness (LW*) when measuring chromaticity on a white background and the brightness (LB*) when measuring chromaticity on a black background using the same specimen, the same measuring device, measurement mode, and light source were measured. The difference between the two (ΔL* = (LW*) - (LB*)) was defined as the light transmittance (ΔL*(W - B)) (average value of n = 3). The L* value is the L* value in the chromaticity (color space) of the L*a*b* color system (JIS Z 8781-4:2013).

[0552] The first light transmittance ΔL 1 *(W - B) of the first sintered body sintered at 1550 °C for 120 minutes and the second light transmittance ΔL 2 *(W - B) of the second sintered body sintered at 1550 °C for 10 minutes were determined, and the ratio of ΔL 2 *(W - B) to ΔL 1 *(W - B) (ΔL 2 *(W - B) / ΔL 1 *(W - B)) was calculated as the change rate of light transmittance.

[0553] Regarding the change rate of light transmittance, a value of 0.85 or more (85% or more) was considered qualified.

[0554] The evaluation results of the zirconia green compacts and zirconia sintered bodies are shown in Table 2.

[0555]

[0556]

[0557] As shown in Table 2, in Comparative Examples 1 to 6, the light transmittance decreased in the short-time sintering with a residence time of 10 minutes at the highest sintering temperature as compared with the sintering with a residence time of 2 hours at the highest sintering temperature.

[0558] In contrast, in Examples 1 to 15, the light transmittance comparable to that of the sintering with a residence time of 2 hours at the highest sintering temperature could be obtained even in the short-time sintering with a residence time of 10 minutes at the highest sintering temperature.

[0559] Industrial applicability

[0560] The zirconia pre-sintered body and composition of the present invention, and the method for producing the same are useful in applications such as dental prostheses as dental materials.

Claims

1. A zirconia green body, which is a zirconia green body formed by consolidating zirconia particles with each other to an extent that sintering is not achieved. It contains zirconia and a stabilizer capable of suppressing the phase transformation of zirconia, and the ΔL of the first sintered body produced by sintering the zirconia green body at 1550 °C for 120 minutes 1 *(W-B) and the ΔL of the second sintered body produced by sintering at 1550 °C for 10 minutes 2 *(W-B) When compared, the following formula (1) is satisfied ΔL 2 *(W - B) / ΔL 1 *(W - B) ≥ 0.85 (1).

2. The zirconia green body according to claim 1, which satisfies 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 zirconia; or (ii) The zirconia contains monoclinic zirconia and cubic zirconia.

3. The zirconia green body according to claim 1 or 2. Wherein, The stabilizer is yttrium oxide (Y 2 O 3 ).

4. The zirconia green body according to claim 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 content rate of the monoclinic system is 55% or more, the content rate of the tetragonal system is 10% or more, and a part of the yttrium oxide is yttrium oxide that is not dissolved in zirconia. (A-2) The zirconia contains tetragonal zirconia, does not conform to (A-1), the content rate of the tetragonal system is 10% or more, and a part of the yttrium oxide is yttrium oxide that is not dissolved in zirconia. (A-3) The zirconia contains monoclinic zirconia and cubic zirconia, the content rate of the monoclinic system is 55% or more, and the content rate of the cubic system is 15% or more. (A-4) The zirconia contains monoclinic zirconia and cubic zirconia, does not conform to (A-3), and the content rate of the cubic system is 15% or more. (A-5) The zirconia contains tetragonal zirconia and cubic zirconia, the content rate of the tetragonal system is 5% or more and less than 50%, the content rate of the cubic system is 50% or more and less than 95%, and a part of the yttrium oxide is yttrium oxide that is not dissolved in zirconia. (A-6) The zirconia contains tetragonal zirconia and cubic zirconia, does not conform to (A-5), the content rate of the cubic system is 10% or more and less than 50%, and a part of the yttrium oxide is yttrium oxide that is not dissolved in zirconia. The content rates of the tetragonal system, cubic system and monoclinic system in (A-1), (A-2), (A-3), (A-4), (A-5) or (A-6) are calculated according to 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 area intensity of the peak near 2θ = 28.2° at the peak top of the main peak of the monoclinic system, I t represents the area intensity of the peak near 2θ = 30.2° at the peak top of the main peak of the tetragonal system, I c represents the area intensity of the peak near 2θ = 30.1° at the peak top of the main peak of the cubic system, I y represents the area intensity of the peak near 2θ = 29.2° at the peak top of the main peak of un-dissolved yttrium oxide.

5. The zirconia green body according to claim 3 or 4. Wherein, The standard deviation of the yttrium element distribution is 2 mol% or more and less than 21 mol%.

6. The zirconia green body according to claim 4 or 5, which satisfies the condition (A-1) or (A-2), and the proportion of yttrium oxide that is not dissolved in zirconia is 1 to 25%.

7. The zirconia green body according to claim 4 or 5, which satisfies the condition (A-3) or (A-4), and a part of the yttrium oxide is yttrium oxide that is not dissolved in zirconia, and the proportion of yttrium oxide that is not dissolved in zirconia is 1 to 15%.

8. The zirconia pre-sintered body according to any one of claims 1 to 7, wherein, the content rate of the stabilizer is 2 to 9 mol% relative to the total moles of zirconia and the stabilizer.

9. The zirconia pre-sintered body according to any one of claims 1 to 8 has a density of 3.6 g / cm 3 or less.

10. The zirconia pre-sintered body according to any one of claims 1 to 9, having an average primary particle size of 40 to 110 nm.

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

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

13. The zirconia composition according to claim 12, satisfying the condition (i), and further containing monoclinic zirconia powder (M).

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 mass%:15.0 mass% to 99.8 mass%:0.2 mass%.

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

16. The zirconia composition according to any one of claims 12 to 15, wherein, the zirconia powder (T) contains a stabilizer capable of suppressing the phase transition of zirconia that has been dissolved, and the content rate of the dissolved stabilizer is 2 to 4 mol% relative to the total moles of zirconia and the stabilizer.

17. The zirconia composition according to claim 12, satisfying the condition (ii), and further, a part of the stabilizer is a stabilizer 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 mass%:15.0 mass% to 100 mass%:0 mass%.

19. The zirconia composition according to claim 12, 17 or 18, wherein, the zirconia powder (C) is 15.0 to 95.0 mass% in the total mass of the zirconia powder (M) and the zirconia powder (C).

20. The zirconia composition according to any one of claims 12, 17 to 19, wherein, the content rate of the stabilizer in the zirconia powder (M) is 0 to 1 mol% relative to the total moles of the zirconia powder (M) and the stabilizer.

21. The zirconia composition according to any one of claims 12, 17 to 20, wherein, The zirconia powder (C) contains a stabilizer that has been solid-solved and can inhibit the phase transformation of zirconia. The content ratio of the solid-solved stabilizer is 5 mol% or more and 15 mol% or less based on the total moles of the zirconia powder (C) and the stabilizer.

22. The zirconia composition according to claim 12, which satisfies the condition (i), further comprises a cubic zirconia powder (T), 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 mass%:12.0 mass% to 99.999 mass%:0.001 mass%.

23. The zirconia composition according to any one of claims 11 to 22, 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 manufacturing a zirconia pre-sintered body, wherein, the zirconia composition according to claims 11 to 23 is calcined to such an extent that the zirconia particles do not reach sintering with each other.

25. A method for manufacturing a zirconia sintered body, wherein, the zirconia pre-sintered body according to claims 1 to 10 is sintered.

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