Zirconium oxide presintered body and method for producing same

Abstract

Provided are: a pre-sintered zirconia having excellent mechanical strength and light transmittance; and a method for producing the pre-sintered zirconia. The present invention relates to a zirconia pre-sintered body containing zirconia and a stabilizer capable of suppressing phase change of zirconia, the zirconia including monoclinic zirconia, and the half-value width of a main peak derived from the monoclinic system in a powder X-ray diffraction pattern by CuK [alpha] rays being 0.18 DEG or more.

Description

Technical Field

[0001] This invention relates to zirconia pre-sintered bodies and methods for manufacturing the same. More specifically, this invention relates to zirconia pre-sintered bodies with excellent mechanical strength and light transmittance, and methods for manufacturing the same. Background Technology

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

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

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

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

[0006] Existing technical documents Patent documents Patent document 1: International Publication No. 2020 / 179877. Summary of the Invention

[0007] The problem the invention aims to solve However, there is room for improvement in physical properties such as light transmittance of the zirconia sintered body obtained by using the zirconia molded body or zirconia pre-sintered body of Patent Document 1.

[0008] Specifically, in Patent Document 1, the total light transmittance was evaluated using a sample with a thickness of 0.5 mm. For example, when used for dental repairs with a thickness of 1.0 mm, there is room for improvement in light transmittance.

[0009] The purpose of this invention is to provide a zirconia pre-sintered body with excellent mechanical strength and light transmittance, and a method for manufacturing the same.

[0010] means for solving problems In order to solve the above-mentioned problems, the inventors conducted repeated and in-depth research and found that by preparing a zirconia pre-sintered body containing zirconia and a stabilizer that can suppress the phase transformation of zirconia, and the zirconia containing the monoclinic crystal system, the zirconia pre-sintered body with a half-width of 0.18° or more in the main peak originating from the monoclinic crystal system in the powder X-ray diffraction pattern based on CuKα rays has excellent mechanical strength and light transmittance. Based on this insight, further research was conducted, and the present invention was completed.

[0011] This invention includes the following inventions.

[0012] [1] A zirconia pre-sintered body comprising zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia. The aforementioned zirconium oxide includes monoclinic zirconium oxide. The half-width of the main peak originating from the aforementioned monoclinic crystal system in the powder X-ray diffraction pattern based on CuKα rays is greater than 0.18°.

[0013] [2] According to the zirconia pre-burnt body described in [1], wherein the aforementioned stabilizer is yttrium oxide.

[0014] [3] According to the zirconia pre-calcined body described in [2], wherein the presence rate f of yttrium oxide not dissolved in zirconia is calculated using the following formula (1-1). y (%) less than 4%.

[0015] f y (%)=I y / (I m +I t +I c +I y )×100 (1-1) (where f) y f represents the presence rate of yttrium oxide that is not dissolved in zirconium oxide. y (%), in XRD determination, I m This represents the area intensity of the peak near 2θ = 28.2° at the apex of the main peak in a monoclinic crystal system; I t This represents the area intensity of the peak near 2θ = 30.3° at the apex of the main peak of the tetragonal crystal system; I c I represents the area intensity of the peak near 2θ = 30.0° at the apex of the main peak in a cubic crystal system; y This represents the area intensity of the peak near 2θ = 29.2° at the apex of the main peak of yttrium oxide, which is not dissolved in zirconium oxide. [4] According to the zirconia pre-sintered body described in [2] or [3], wherein the monoclinic crystal ratio f calculated using the following formula (1-2) m (%) Less than 55%.

[0016] f m (%) = I m / (I m +I t +I c +I y )×100 (1-2) (where f) m Indicates the monoclinic crystallinity (%); in XRD measurements, I m This represents the area intensity of the peak near 2θ = 28.2° at the apex of the main peak in a monoclinic crystal system; I t This represents the area intensity of the peak near 2θ = 30.3° at the apex of the main peak of the tetragonal crystal system; I c I represents the area intensity of the peak near 2θ = 30.0° at the apex of the main peak in a cubic crystal system; y This represents the area intensity of the peak near 2θ = 29.2° at the apex of the main peak of yttrium oxide, which is not dissolved in zirconium oxide. [5] According to the zirconia pre-calcined body described in [4], wherein the aforementioned monoclinic crystal ratio f m (%) less than 50%.

[0017] [6] The zirconia pre-fired body according to any one of [1] to [5], wherein the average primary particle size comprises primary particles of 60 nm or more and less than 250 nm.

[0018] [7] The zirconia pre-calcined body according to any one of [1] to [6], wherein the content of the aforementioned stabilizer is 2 to 10 mol relative to the total molar of the aforementioned zirconia and stabilizer.

[0019] The method for manufacturing the zirconia pre-fired body as described in any one of [8][1]~[7] includes: A process for manufacturing a zirconia composition comprising zirconia particles and stabilizer particles capable of inhibiting the phase transformation of zirconia; The pulverization process for pulverizing the aforementioned zirconium oxide composition; A molding process for obtaining a molded article by molding a pulverized zirconium oxide composition; and The pre-firing process for pre-firing the aforementioned molded body. The aforementioned zirconia particles include monoclinic zirconia particles. In the aforementioned pulverizing process, (i) a pulverizing medium with a diameter of less than 1 mm is used and the pulverizing time is more than 10 minutes, or (ii) a pulverizing medium with a diameter of more than 1 mm is used and the pulverizing time exceeds 40 hours.

[0020] [9] The method for manufacturing zirconia pre-fired body according to [8], wherein the pre-firing temperature in the aforementioned pre-firing process is 600~1200℃.

[0021]

[10] A method for manufacturing a zirconia sintered body, wherein the zirconia pre-sintered body described in any one of [1] to [7] is calcined at atmospheric pressure at a maximum sintering temperature exceeding 1200°C and below 1650°C.

[0022] Invention Effects According to the present invention, a zirconia pre-sintered body with excellent mechanical strength and light transmittance (linear light transmittance and total light transmittance) of the obtained zirconia sintered body, and a method thereof are provided.

[0023] Furthermore, according to the present invention, the resulting zirconia sintered body has a high total light transmittance even when the thickness is 1.0 mm, and excellent light transmittance, thus exhibiting excellent aesthetics when manufacturing dental materials (e.g., dental repairs).

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

[0025] Furthermore, by using the zirconia pre-sintered body of the present invention, a zirconia sintered body with excellent light transmittance can be obtained during short-term sintering with a holding time of less than 10 minutes at the highest sintering temperature. Therefore, it helps to further improve productivity, such as shortening treatment time in dental hospitals, and facilitates treatment with dental fillings in a single visit (i.e., single-visit treatment).

[0026] Furthermore, by using the zirconia pre-sintered body of the present invention, a zirconia sintered body with excellent mechanical strength and linear light transmittance can be provided without the need for a HIP device.

[0027] Furthermore, according to the present invention, even when the molded body is large (e.g., 20 mm thick), a pre-fired body can be obtained without problems such as degreasing cracks. Detailed Implementation

[0028] [Zirconium oxide pre-fired body] The zirconia pre-sintered body of the present invention is a zirconia pre-sintered body containing zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia. The aforementioned zirconium oxide includes monoclinic zirconium oxide. The half-width at half-maximum (WWHM) of the main peak originating from the aforementioned monoclinic crystal system in the powder X-ray diffraction pattern based on CuKα rays (hereinafter referred to as "WWHM of the main peak originating from the monoclinic crystal system" or "WWHM") is greater than 0.18°.

[0029] In this specification, "zirconia composition" refers to a composition containing zirconia powder and stabilizer powder.

[0030] In this specification, "molded body" refers to an object that has not reached the semi-sintered state (pre-sintered state) or the sintered state. That is, the molded body is distinguished from the pre-sintered body and the sintered body in that it has not been calcined after being formed by molding.

[0031] In this specification, "zirconia pre-sintered body" refers to a semi-sintered object in which zirconia particles are necked (fixed) together and are not fully sintered.

[0032] In this specification, "zirconia sintered body" refers to an object in a sintered state where zirconia particles are completely sintered. In a zirconia sintered body, the zirconia particles are bonded together by sintering, and as sintering progresses, the relative density increases, resulting in densification. Therefore, it exhibits a fully sintered state with a relative density of over 95%.

[0033] In this specification, "zirconia" refers to zirconia (IV) (ZrO2), where ZrO2 particles contain trace amounts (more than 0.5% by mass and less than 3% by mass) of HfO2 relative to the amount of ZrO2. HfO2 is difficult to separate; therefore, terms such as "zirconia," "zirconia particles," and "zirconia powder" refer to substances containing both ZrO2 and HfO2. Furthermore, particles and / or powders of stabilizers dissolved in zirconia are also included in "zirconia particles" and "zirconia powder," respectively.

[0034] In this specification, "half-value width" refers to the half-value total width (FWHM).

[0035] In this instruction manual, "atmospheric pressure" refers to standard atmospheric pressure (1 atm).

[0036] It should be noted that the upper and lower limits of the numerical ranges (temperature range, content of each component, presence rate of crystal system, values ​​calculated from components, and various physical properties, etc.) in this specification can be appropriately combined.

[0037] The reason why the main peak of the zirconia pre-sintered body of the present invention has a half-width of the monoclinic crystal system is within a specified range, and the mechanical strength and light transmittance (linear light transmittance and total light transmittance) of the resulting zirconia sintered body are excellent is not yet clear, but it is speculated as follows.

[0038] Due to the reduced crystallinity of the zirconia pre-sintered body, sintering at lower temperatures can be achieved compared to previous materials. As a result, the sintered body has a smaller and more uniform grain size, and yields a sintered body with good mechanical strength and light transmittance (linear light transmittance and total light transmittance).

[0039] In the zirconia pre-sintered body of the present invention, from the viewpoint that sintering at low temperatures is easily possible and from the viewpoint that sintered bodies with excellent mechanical strength, linear light transmittance and total light transmittance are easily obtained, the half-width of the main peak originating from the monoclinic crystal system is preferably 0.19° or more, more preferably 0.20° or more, further preferably 0.21° or more, and particularly preferably 0.22° or more.

[0040] It should be noted that the upper limit of the half-width of the main peak originating from the monoclinic crystal system is not particularly limited as long as it can achieve the effect of the present invention. For example, it can also be below 0.5°, below 0.45°, or below 0.4°.

[0041] The zirconia pre-burnt body contains a stabilizer (hereinafter also referred to as "stabilizer") that can suppress the phase transformation of zirconia.

[0042] The content of stabilizer in the zirconia pre-sintered body is preferably 2.0 mol% or more, more preferably 3.0 mol% or more, further preferably 3.5 mol% or more, and particularly preferably 4.0 mol% or more, relative to the total molar content of zirconia and stabilizer. When it is 2.0 mol% or more, it is preferred because the sintered body contains more cubic crystal systems, which improves light transmittance (linear light transmittance and total light transmittance).

[0043] Furthermore, the content of the aforementioned stabilizer is preferably 10 mol% or less, more preferably 9.0 mol% or less, even more preferably 8.5 mol% or less, and particularly preferably 8 mol% or less. A content of 10 mol% or less is preferred from the perspective of preventing a decrease in mechanical strength.

[0044] Stabilizers (hereinafter also referred to as "stabilizers") that can suppress the zirconium oxide phase transformation include, for example, calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y2O3), cerium oxide (CeO2), scandium oxide (Sc2O3), niobium oxide (Nb2O5), lanthanum oxide (La2O3), erbium oxide (Er2O3), and praseodymium oxide (Pr2O3, Pr6O3). 11 Oxides such as samarium oxide (Sm₂O₃), europium oxide (Eu₂O₃), thulium oxide (Tm₂O₃), gallium oxide (Ga₂O₃), indium oxide (In₂O₃), and yttrium oxide (Yb₂O₃) are preferred. One of the aforementioned stabilizers may be used alone, or two or more may be used in combination.

[0045] In the zirconia pre-calcined body of the present invention, the stabilizer may be only yttrium oxide (Y2O3), or may further include yttrium oxide and other stabilizers that can suppress the phase transformation of zirconia besides yttrium oxide.

[0046] Furthermore, in the zirconia pre-sintered body of the present invention, from the viewpoint that the half-width of the main peak of zirconia originating from the monoclinic crystal system is integrated within a specified range, and the resulting sintered body has superior mechanical strength and light transmittance (linear light transmittance and total light transmittance), the presence rate f of yttrium oxide (hereinafter also simply referred to as "undissolved yttrium oxide") not dissolved in zirconia is calculated using the following formula (1-1). y (%) is preferably less than 4%. It should be noted that f y (%) is not particularly limited as long as the effect of the present invention can be achieved; it can be less than 10%, less than 7%, or less than 5%.

[0047] As a suitable implementation, a zirconia pre-fired body with fy (%) of 4% or more and less than 7% can be cited.

[0048] f y (%)=I y / (I m +I t +I c +I y )×100 (1-1) (where f) y f represents the presence rate of yttrium oxide that is not dissolved in zirconium oxide. y (%), in XRD determination, I m I represents the area intensity of the peak near 2θ = 28.2° at the apex of the main peak in a monoclinic crystal system. t I represents the area intensity of the peak near 2θ = 30.3° at the apex of the main peak of the tetragonal crystal system. c I represents the area intensity of the peak near 2θ = 30.0° at the apex of the main peak in a cubic crystal system. y This represents the area intensity of the peak near 2θ = 29.2° at the apex of the main peak of yttrium oxide, which is not dissolved in zirconium oxide. From the perspective that the zirconia sintered body obtained by acting integrally within the specified range through the aforementioned half-width has superior mechanical strength and light transmittance (linear light transmittance and total light transmittance), the presence rate f of undissolved yttrium oxide is considered. y (%) is more preferably less than 3.5%, further preferably less than 2%, and particularly preferably less than 1%.

[0049] Furthermore, the presence rate f of unsolidified yttrium oxide y (%) can be 0%.

[0050] The presence rate f of unsolvable yttrium oxide y (%) can be adjusted by methods such as pulverization, as described below.

[0051] Furthermore, in the zirconia pre-sintered body of the present invention, from the viewpoint that the half-width of the main peak of the monoclinic crystal system of zirconia is within a specified range and is integrated, resulting in a sintered body with superior mechanical strength and light transmittance (linear light transmittance and total light transmittance), the monoclinic crystal ratio f calculated using formula (1-2) is preferred. m (%) Less than 55%.

[0052] f m (%) = I m / (I m +I t +I c +I y )×100 (1-2) (where f) m Indicates the monoclinic crystallinity (%); in XRD measurements, I m This represents the area intensity of the peak near 2θ = 28.2° at the apex of the main peak in a monoclinic crystal system; I t This represents the area intensity of the peak near 2θ = 30.3° at the apex of the main peak of the tetragonal crystal system; I c I represents the area intensity of the peak near 2θ = 30.0° at the apex of the main peak in a cubic crystal system; y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak of yttrium oxide, which is not dissolved in zirconium oxide.

[0053] From the viewpoint that the zirconia sintered body obtained by acting integrally within the aforementioned half-value width in the zirconia pre-sintered body has superior mechanical strength and light transmittance (linear light transmittance and total light transmittance), the monoclinic crystallinity f m (%) is more preferably less than 50%, further preferably less than 48%, and particularly preferably less than 45%.

[0054] In addition, the monoclinic crystal ratio f m (%) is preferably 5% or more, more preferably 10% or more, even more preferably 15% or more, and particularly preferably 20% or more.

[0055] The zirconia pre-fired body of the present invention preferably contains primary particles with an average primary particle size of 60 nm or more and less than 250 nm.

[0056] From the viewpoint of suppressing the reduction of light transmittance, while having excellent mechanical strength and light transmittance, especially superior linear light transmittance, the aforementioned average primary particle size is more preferably 61 nm or more, further preferably 62 nm or more, and particularly preferably 63 nm or more.

[0057] Furthermore, the aforementioned average primary particle size is more preferably 220 nm or less, even more preferably 200 nm or less, and particularly preferably 180 nm or less.

[0058] In the zirconia pre-fired body of the present invention, the average primary particle size can be appropriately selected as long as it is within the aforementioned suitable range.

[0059] In a suitable embodiment, from the viewpoint that zirconia sintered bodies with excellent mechanical strength and light transmittance can be easily obtained even at the highest sintering temperature (e.g., below 1450°C) at low temperatures compared to the past, a zirconia pre-sintered body containing primary particles with an average primary particle size of 60 nm or more and less than 80 nm can be cited.

[0060] Other suitable embodiments include zirconia pre-fired bodies comprising primary particles with an average primary particle size of 80 nm or more and less than 200 nm.

[0061] The method for evaluating the average primary particle size is as described in the examples below.

[0062] The zirconia pre-fired body of the present invention can contain additives other than zirconia and stabilizers, as long as the effects of the present invention are achieved. Examples of such additives include colorants (including pigments, composite pigments and fluorescent agents), alumina (Al2O3), titanium dioxide (TiO2), and silicon dioxide (SiO2).

[0063] As the aforementioned pigment, examples include oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically NiO, Cr2O3, etc.) (excluding Y2O3 and CeO2), preferably oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb, and more preferably oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb.

[0064] In addition, the zirconia pre-calcined body of the present invention may be free of erbium oxide (Er2O3).

[0065] Examples of composite pigments include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, and (Co,Zn)Al2O4. Examples of fluorescent agents include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl. 10 O 17 Eu et al.

[0066] The zirconia pre-sintered body of the present invention may contain a fluorescent agent. By containing a fluorescent agent in the zirconia pre-sintered body, the zirconia sintered body acquires fluorescence. The type of fluorescent agent is not particularly limited, and one or more substances capable of emitting fluorescence using light of any wavelength may be used.

[0067] Examples of fluorescent agents include substances containing metallic elements. Examples of such metallic elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one or more of these metallic elements. Among these metallic elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred.

[0068] Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the aforementioned metal elements. Other fluorescent agents include Y₂SiO₅:Ce, Y₂SiO₅:Tb, (Y,Gd,Eu)BO₃, Y₂O₃:Eu, YAG:Ce, ZnGa₂O₄:Zn, and BaMgAl. 10 O 17 Eu et al.

[0069] The content of fluorescent agent in the zirconia pre-sintered body is not particularly limited, and can be appropriately adjusted according to the type of fluorescent agent or the purpose of the zirconia sintered body. From the viewpoint that it can be preferably used as a dental patch, the content is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, relative to 100% by mass of zirconia contained in the zirconia pre-sintered body and calculated according to the oxide of the metal element contained in the fluorescent agent.

[0070] Furthermore, the content of the fluorescent agent is calculated based on the oxide of the metal element contained in the fluorescent agent. There is no particular limitation as long as it exhibits suitable fluorescence; it can be set to less than 1% by mass, less than 0.5% by mass, or less than 0.1% by mass. By keeping this content above the lower limit mentioned above, the fluorescence is comparable to that of natural human teeth. In addition, by keeping this content below the upper limit mentioned above, the reduction in mechanical strength and light transmittance can be suppressed.

[0071] Furthermore, to ensure sufficient mechanical strength for machining in the pre-sintered state, the flexural strength of the zirconia pre-sintered body of the present invention is preferably 15 MPa or more. Additionally, to facilitate machining in the pre-sintered state, the flexural strength of the zirconia pre-sintered body is preferably 70 MPa or less, more preferably 60 MPa or less.

[0072] The aforementioned bending strength was determined according to ISO 6872:2015 (Dentistry - Ceramic materials), with only the dimensions of the test piece changed; a test piece measuring 5mm × 10mm × 50mm was used. The front and C-side of the test piece (the side formed by chamfering the corners of the test piece at a 45° angle) were finished along the length using 600-grit sandpaper. The test piece was positioned with its widest face facing the vertical direction (load direction). In the three-point bending test, the distance between the support points (span) was set to 30mm, and the crosshead speed was set to 0.5mm / minute.

[0073] Furthermore, the density of the zirconia pre-fired body of the present invention is preferably 2.7 g / cm³. 3 The above, more preferably 3.0 g / cm 3 The above is further preferred to be 3.2 g / cm³. 3 above.

[0074] In addition, the density of the zirconia pre-sintered body is preferably 4.0 g / cm³. 3 The preferred value is 3.8 g / cm³. 3 The following is a further preferred value: 3.6 g / cm³ 3 The following applies. When the density is within the aforementioned range, molding can be easily performed.

[0075] The density of the zirconia pre-sintered body can be calculated using the formula (mass of the zirconia pre-sintered body) / (volume of the zirconia pre-sintered body). For example, to determine the density of the zirconia pre-sintered body, one can change the cutting position of the zirconia pre-sintered body while cutting out 10mm square test pieces (n=3) at arbitrary locations. The mass and volume of the obtained test pieces are measured, and the arithmetic mean of the measured values ​​is calculated. Using this arithmetic mean, the density is calculated according to the formula above.

[0076] [Manufacturing method of zirconia pre-sintered body] The following manufacturing methods can be cited as examples of methods for manufacturing zirconia pre-fired bodies: It includes: A process for manufacturing a zirconia composition comprising zirconia particles and stabilizer particles capable of inhibiting the phase transformation of zirconia; The pulverization process for pulverizing the aforementioned zirconium oxide composition; A molding process for obtaining a molded article by molding a pulverized zirconium oxide composition; and The pre-firing process for pre-firing the aforementioned molded body. The aforementioned zirconia particles include monoclinic zirconia particles. The aforementioned pulverizing process includes the pulverizing treatment specified below.

[0077] Next, the manufacturing method of zirconia pre-sintered body will be explained using yttrium oxide as an example.

[0078] The zirconia pre-fired body of the present invention can be manufactured by the following operation: pulverizing a zirconia composition, and calcining (pre-firing) a shaped body formed by molding the pulverized zirconia composition until the zirconia particles are not sintered together. In the aforementioned pulverization process, energy is applied excessively compared to the prior art through pulverization under specified conditions.

[0079] A zirconia composition prior to pulverization is prepared by mixing zirconia powder, used as a raw material powder, with yttrium oxide powder. The mixing method is not particularly limited, and known methods and apparatus can be used.

[0080] As a method for preparing zirconia particles constituting zirconia powder and yttrium oxide particles constituting yttrium oxide powder, a crushing process that achieves micronization by crushing or breaking down coarse particles can be adopted, for example, an aggregation process by which atoms or ions are synthesized through a nucleation and growth process. Considering that a prescribed crushing process must be performed in order to obtain the desired half-width in the zirconia pre-burnt body obtained during the aggregation process, from the viewpoint of easy manufacturing, a crushing process is preferred.

[0081] The following explanation of the manufacturing method of zirconium oxide compositions can be illustrated by taking the crushing process as an example.

[0082] The zirconium oxide constituting the aforementioned zirconium oxide powder may include monoclinic zirconium oxide.

[0083] As the zirconium oxide constituting the aforementioned zirconium oxide powder, as long as it contains monoclinic zirconium oxide, it may further contain tetragonal zirconium oxide and / or cubic zirconium oxide.

[0084] In zirconium oxide powder, as long as it contains monoclinic zirconium oxide, one of these crystal systems can be used alone, or two or more can be used in combination.

[0085] As zirconium oxide powder, commercially available zirconium oxide particles can be used, or commercially available powder can be pulverized using a known pulverizing and mixing device (ball mill, etc.) before use.

[0086] As yttrium oxide powder, commercially available yttrium oxide particles can be used, or commercially available powder can be pulverized using a known pulverizing and mixing device (ball mill, etc.) before use.

[0087] Commercially available zirconium oxide powders include, for example, those marketed under the trade names "Zpex (registered trademark)" (Y₂O₃ content: 3 mol%), "Zpex (registered trademark) 4" (Y₂O₃ content: 4 mol%), "Zpex (registered trademark) Smile (registered trademark)" (Y₂O₃ content: 5.5 mol%), "TZ-3Y" (Y₂O₃ content: 3 mol%), "TZ-3YS" (Y₂O₃ content: 3 mol%), "TZ-4YS" (Y₂O₃ content: 4 mol%), "TZ-6Y" (Y₂O₃ content: 6 mol%), "TZ-6YS" (Y₂O₃ content: 6 mol%), "TZ-8YS" (Y₂O₃ content: 8 mol%), and "TZ..." -10YS (Y2O3 content: 10 mol%), "TZ-3Y-E" (Y2O3 content: 3 mol%), "TZ-3YS-E" (Y2O3 content: 3 mol%), "TZ-3YB-E" (Y2O3 content: 3 mol%), "TZ-3YSB-E" (Y2O3 content: 3 mol%), "TZ-3YB" (Y2O3 content: 3 mol%), "TZ-3YSB" (Y2O3 content: 3 mol%), "TZ-3Y20AB" (Y2O3 content: 3 mol%), "TZ-8YSB" (Y2O3 content: 8 mol%), "TZ-0" (Y2O3 content: 0 mol%; monoclinic zirconia); all of the above are manufactured by Tosoh Corporation, etc.

[0088] Next, a zirconium oxide composition containing zirconium oxide particles with a monoclinic crystal system and stabilizer particles is subjected to a pulverization process.

[0089] In a pulverization process under specified conditions, by applying excessive energy compared to existing technologies, a calcined zirconia prebody with the half-width of the main peak of the monoclinic crystal system derived from zirconia can be obtained when using the pulverized zirconia composition, and the half-width of the main peak of zirconia derived from the monoclinic crystal system is adjusted to the desired range.

[0090] Previously, regarding zirconia particles, since zirconia itself is a very hard material, it was difficult to excessively reduce the size of zirconia particles even if the energy value of the crushing process was increased. From this point of view, no technical significance was found in excessive crushing.

[0091] However, it can be inferred that in this invention, a zirconium oxide composition containing monoclinic zirconium oxide and yttrium oxide is subjected to a pulverization process. Compared with the prior art, if the energy in the pulverization process is excessively applied, the half-width of the main peak of the monoclinic zirconium oxide in the zirconium oxide pre-sintered body obtained by using the pulverized zirconium oxide composition can be adjusted to the desired range. When manufacturing a sintered body, in addition to excellent mechanical strength, both linear light transmittance and total light transmittance are excellent, exhibiting excellent light transmittance.

[0092] By adjusting the half-width of the main peak of the monoclinic zirconium oxide in the zirconia pre-sintered body to the desired range, in addition to the excellent mechanical strength of the final sintered body, the sintered body can exhibit excellent light transmittance, both in terms of linear light transmittance and total light transmittance. From the viewpoint of applying excessive energy to the zirconium oxide composition, the following method is preferred as a specific operation in the pulverization process.

[0093] (i) Use a grinding medium with a diameter of less than 1 mm and a grinding time of more than 10 minutes, or (ii) Use a grinding medium with a diameter of more than 1 mm and a grinding time of more than 40 hours.

[0094] By using these methods to disintegrate and pulverize, crystallinity is reduced and half-width is widened, allowing the half-width of the main peak of the monoclinic zirconia in the resulting zirconia pre-burnt body to be adjusted to the desired range.

[0095] Furthermore, by performing solid solution and amorphization of yttrium oxide during these pulverization processes, the presence rate of undissolved yttrium oxide, calculated using equation (1-1), can be adjusted. The presence rate of undissolved yttrium oxide can be controlled by adjusting the pulverization time.

[0096] When using a grinding medium with a diameter of less than 1 mm, the diameter of the grinding medium is preferably 0.1 to 0.5 mm, based on the viewpoint that by using a grinding medium with a fine diameter, it is easy to widen the half-width and the half-width of the main peak of the monoclinic zirconium oxide in the resulting zirconium oxide pre-burnt body can be easily adjusted to the desired range.

[0097] Commercially available products can be used as pulverizing media with a diameter of less than 1 mm.

[0098] Examples of grinding devices that use grinding media with a diameter of less than 1 mm include bead mills.

[0099] When using a pulverizing medium with a diameter of less than 1 mm, the pulverizing time is not particularly limited as long as the half-width of the main peak of the monoclinic zirconium oxide in the obtained zirconia pre-sintered body can be easily widened and adjusted to the desired range. From the viewpoint that the half-width of the main peak of the monoclinic zirconium oxide in the obtained zirconia pre-sintered body can be easily adjusted to the desired range, it is preferably 10 minutes or more, more preferably 15 minutes or more, further preferably 20 minutes or more, and particularly preferably 30 minutes or more. Furthermore, from the viewpoint that the half-width of the main peak of the monoclinic zirconium oxide in the obtained zirconia pre-sintered body can be easily adjusted to the desired range, the pulverizing time is preferably 20 hours or less, more preferably 10 hours or less, further preferably 5 hours or less, and particularly preferably 2 hours or less.

[0100] It should be noted that when using a pulverizing device that circulates the slurry while pulverizing (such as a circulating bead mill) as a pulverizing device, the pulverizing time refers to the residence time of the slurry in the container (pulverizing chamber).

[0101] When using a grinding medium with a diameter of 1 mm or more, from the viewpoint that the diameter of the grinding medium is 1.5 mm or more, and more preferably 2.0 mm or more, the diameter of the grinding medium is preferably 1.5 mm or more, and more preferably 2.0 mm or more, as the diameter of the grinding medium.

[0102] Commercially available products can be used as pulverizing media with a diameter of 1 mm or more.

[0103] Examples of grinding devices that use grinding media with a diameter of 1 mm or more include ball mills.

[0104] When using a pulverizing medium with a diameter of 1 mm or more, the pulverizing time (pulverization treatment time) is not particularly limited as long as it can adjust the half-width of the main peak of the monoclinic zirconia in the resulting zirconia pre-calcined body to the desired range. It is preferably more than 40 hours, more preferably more than 55 hours, and especially from the viewpoint of easily adjusting the aforementioned half-width to the desired range, more preferably more than 80 hours, and particularly preferably more than 100 hours. Furthermore, the pulverization treatment time is preferably less than 1000 hours, more preferably less than 800 hours, more preferably less than 500 hours, and particularly preferably less than 300 hours.

[0105] In this invention, by supplying the zirconia composition with pulverizing energy that is adjusted and increased according to the combination of pulverizing time and pulverizing medium diameter, a zirconia composition containing zirconia particles in which the half-width of the main peak of the monoclinic zirconia in the resulting zirconia pre-burnt body is adjusted to the desired range can be obtained.

[0106] It can be inferred that by using the zirconia composition obtained as described above to manufacture zirconia pre-sintered bodies, the zirconia pre-sintered bodies of the present invention, in addition to having excellent mechanical strength, also exhibit excellent linear light transmittance and total light transmittance, thus demonstrating excellent light transmittance.

[0107] The zirconium oxide composition before and after pulverization can be in the form of particles, slurry, etc.

[0108] When the zirconium oxide composition is a slurry, the slurry can be manufactured by mixing the mixed powder obtained by pulverization with a solvent (suitably water).

[0109] From the viewpoint of excellent mechanical strength and light transmittance of the pulverized zirconia composition, the average particle size is preferably 0.2 μm or less. Furthermore, from the viewpoint of excellent formability, it is preferably 20 nm or more.

[0110] The average particle size of the zirconia and yttrium oxide particles in the pulverized zirconia composition can be determined by a dynamic light scattering particle size distribution measurement method. For example, a dynamic light scattering particle size distribution measurement device (trade name "SZ-100V2") manufactured by Horiba Corporation can be used to subject a slurry diluted with water to approximately 0.1% by mass to ultrasonic irradiation for 30 minutes, followed by measurement based on volume while in contact with ultrasonic waves.

[0111] In addition, the zirconia composition may contain additives such as binders, dispersants, emulsifiers, defoamers, pH adjusters, lubricants, and light transmittance adjusters. One additive may be used alone, or two or more may be used in combination.

[0112] Examples of adhesives include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic adhesives, wax adhesives, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.

[0113] To improve light transmittance, the binder content in the zirconium oxide composition of the present invention is preferably 10% by mass or less relative to 100% by mass of zirconium oxide, more preferably 7% by mass or less, and even more preferably 5% by mass or less.

[0114] Examples of plasticizers include polyethylene glycol, glycerin, propylene glycol, and dibutylphthalic acid.

[0115] Examples of dispersants include ammonium polycarboxylate (such as triammonium citrate), ammonium polyacrylate, acrylic copolymer resins, acrylate copolymers, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (such as polyoxyethylene lauryl ether phosphate and polyoxyethylene alkyl ether phosphate), nonionic surfactants, glyceryl oleate, amine salt surfactants, oligosaccharide alcohols, stearic acid, etc.

[0116] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitol derivatives.

[0117] Examples of defoaming agents include alcohols, polyethers, polyethylene glycols, silicones, and waxes.

[0118] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxide such as tetramethylammonium hydroxide).

[0119] Examples of lubricants include polyoxyethylene alkyl ethers and waxes.

[0120] Examples of light transmittance modifiers include aluminum oxide (Al2O3), titanium dioxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0121] The BET specific surface area of ​​the particles constituting the zirconia composition, when measured according to JIS Z 8830:2013, is preferably 7.0 m². 2 / g or more, preferably 7.5m 2 / g or more, further preferably 8.0m 2 / g or more. At 7.0m 2 When the surface area is above a certain value (e.g.), it is easier to suppress the formation of white turbidity in the sintered body during sintering. Furthermore, the preferred BET specific surface area is 50 m² / g. 2 / g or less, preferably 45m 2 / g or less, more preferably 40m 2 / g or less. At 50m 2 When the content is below / g, it is not easily affected by uneven temperature inside the calcining furnace.

[0122] BET surface area can be measured using commercially available devices such as the fully automated surface area measuring device (trade name "Macsorb (registered trademark) HMmodel-1200", BET flow method (single-point method / multi-point method), manufactured by Mountech). For example, the aforementioned fully automated surface area measuring device can be used to perform the measurement using the BET flow method (single-point method).

[0123] Furthermore, the light transmittance of the sintered body is not easily reduced when the calcination time for sintering is shortened. The "BET specific surface area" mentioned here refers to the specific surface area measured without distinguishing between primary and secondary particles.

[0124] Next, a molded body is produced by molding the pulverized zirconium oxide composition. The molded body is obtained by applying external force to the zirconium oxide composition and molding it using a known method.

[0125] There are no particular limitations on the molding method; for example, the following methods can be used.

[0126] (a) A process of casting a slurry containing a pulverized zirconium oxide composition; (b) A process of gel casting a slurry containing a pulverized zirconium oxide composition; (c) The process of pressing the pulverized zirconium oxide composition into shape; (d) A process for molding a zirconium oxide composition comprising zirconium oxide particles, yttrium oxide particles and resin; (e) A step of polymerizing a zirconium oxide composition comprising zirconium oxide particles, yttrium oxide particles, and polymerizable monomers and / or oligomers; and (f) A process for stacking particles containing zirconium oxide particles and yttrium oxide particles.

[0127] (a) Powder slurry pouring When manufacturing zirconia molded bodies using a method that involves casting a slurry containing a pulverized zirconia composition, the specific method of casting the slurry is not particularly limited, and methods such as drying the slurry after it has been poured into a mold can be employed.

[0128] From the perspective of facilitating the flow of slurry into the mold, preventing excessive drying time, and increasing the number of times the mold can be used, the content of the dispersion medium in the slurry is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less.

[0129] The slurry can be poured into the mold under normal pressure, but from the point of view of production efficiency, it is preferable to do so under pressure.

[0130] (b) Gel casting When manufacturing a zirconia molded body by means of a process of gel casting a slurry containing a pulverized zirconia composition, the specific method of gel casting is not particularly limited. For example, a method can be used to obtain a shaped wet body by gelling the aforementioned slurry in a mold and then drying it.

[0131] From the perspective of preventing excessive drying time and suppressing cracks during drying, the content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less.

[0132] Gelation can be achieved, for example, by adding a gelling agent, or by polymerizing a polymerizable monomer after its addition.

[0133] There are no restrictions on the type of gelling agent; water-soluble gelling agents can be used, with agarose and gelatin being preferred. A single gelling agent can be used, or two or more can be used in combination. The amount of gelling agent used is not particularly limited as long as it does not cause problems such as cracking during sintering. Depending on the mass of the slurry after mixing the gelling agent, it can be set to less than 10% by mass, less than 5% by mass, or less than 1% by mass.

[0134] Furthermore, there are no particular limitations on the types of polymerizable monomers. Examples include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, erythritol mono(meth)acrylate, and other (meth)acrylate monomers; N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N,N-bis(2-hydroxyethyl)(meth)acrylamide, and other (meth)acrylamide monomers. A single polymerizable monomer can be used, or two or more monomers can be used in combination.

[0135] There is no particular limit to the amount of polymerizable monomers used, as long as problems such as cracking during sintering do not occur. Depending on the quality of the slurry after mixing the polymerizable monomers, it can be set to less than 10% by mass, less than 5% by mass, or less than 1% by mass.

[0136] When gelation is achieved by polymerization of polymerizable monomers, a polymerization initiator is preferably used. The type of polymerization initiator is not particularly limited, but photopolymerization initiators are particularly preferred. As a photopolymerization initiator, it is appropriate to select from those commonly used in industry, with photopolymerization initiators used in dental applications being preferred.

[0137] Specific examples of photopolymerization initiators include (bis)acylphosphine oxides (including salts), thioxanthones (including quaternary ammonium salts), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ethers, and α-aminoketone compounds. A single photopolymerization initiator can be used alone, or two or more can be used in combination. Among these photopolymerization initiators, at least one selected from (bis)acylphosphine oxides and α-diketones is preferred. This allows polymerization (gelation) to occur in both the ultraviolet (including near-ultraviolet) and visible light regions. In particular, polymerization (gelation) can be fully achieved even when using any light source, such as Ar lasers, He-Cd lasers, halogen lamps, xenon lamps, metal halide lamps, light-emitting diodes (LEDs), mercury lamps, and fluorescent lamps.

[0138] There are no particular limitations on the drying method used to dry the shaped wet body. Examples include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. One or more of these methods may be used. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred in order to suppress the formation of cracks during drying.

[0139] There are no particular limitations on the types of molds used in slurry casting and gel casting. For example, porous molds made of plaster, resin, ceramics, etc., and non-porous molds made of metal, resin, etc., can be used.

[0140] (c) Pressure molding In the process of press molding the pulverized zirconium oxide composition, there is no particular limitation on the specific method of press molding, and a known press molding machine can be used.

[0141] Specific methods of pressure molding include, for example, uniaxial pressure molding.

[0142] In addition, multi-stage molding can be performed. For example, after the zirconia composition is press-molded, it can be further subjected to CIP (Cold Isostatic Pressing) treatment.

[0143] The shape of the aforementioned molded body is not particularly limited and can be disc-shaped, cuboid-shaped, or in the shape of a dental product (e.g., a crown).

[0144] The molded body can be, for example, a columnar zirconia molded body in which a zirconia composition (e.g., particles) is filled into a mold and compacted by uniaxial pressure.

[0145] The higher the surface pressure during pressure molding, the higher the density of the molded body. On the other hand, if the density of the zirconia molded body is too high, the zirconia pre-sintered body will harden. Therefore, the surface pressure during pressure molding of zirconia molded bodies is preferably 30~200 MPa. When the surface pressure is 30 MPa or higher, the shape retention of the zirconia molded body is excellent. In addition, when the pressure is below 200 MPa, the density of the zirconia molded body will not increase excessively, making it easier to prevent hardening.

[0146] The aforementioned molded articles also include those that have been densified by high-temperature pressure treatment, such as CIP (Cold Isostatic Pressing).

[0147] Based on the same viewpoint as mentioned above, the CIP pressure is preferably 30~200MPa.

[0148] (d) Molding of a zirconia composition containing resin When a zirconia molded body is manufactured by means of a step of molding a zirconia composition comprising zirconia particles, yttrium oxide particles and resin, the specific method used to mold the zirconia composition is not particularly limited, and can be, for example, injection molding, injection molding, extrusion molding, etc.

[0149] Alternatively, molding methods such as hot-melt dissolution (FDM), inkjet printing, and powder / binder lamination (3D printing, etc.) can be used. Among these molding methods, injection molding and injection molding are preferred, and injection molding is more preferred.

[0150] There is no particular limitation on the type of resin mentioned above, but the aforementioned adhesive is preferred.

[0151] (e) Polymerization of a zirconium oxide composition comprising zirconium oxide particles, yttrium oxide particles and containing polymerizable monomers and / or oligomers Curing can be achieved by polymerizing a zirconium oxide composition containing zirconium oxide particles, yttrium oxide particles, and polymerizable monomers and / or oligomers, thereby polymerizing the polymerizable monomers and / or oligomers in the composition.

[0152] When manufacturing zirconia molded bodies using a method that includes this polymerization process, the specific method is not particularly limited. For example, a method that polymerizes the zirconia composition within a mold can be used; a photolithography method (stereolithography; SLA) using the zirconia composition can also be employed. Among these, (b) photolithography (SLA) is preferred.

[0153] According to the photoforming method, a shape corresponding to the desired shape of the final sintered zirconia body can be imparted at a specific point in time during the manufacturing of the zirconia molded body. Therefore, this photoforming method is sometimes particularly suitable for cases where the sintered zirconia body is used as a dental material such as dental repairs.

[0154] There is no particular limitation on the type of polymerizable monomer. It can be any of the following: monofunctional (meth)acrylates, monofunctional (meth)acrylamides, etc.; and multifunctional polymerizable monomers such as difunctional aromatic compounds, difunctional aliphatic compounds, and trifunctional or higher compounds. One type of polymerizable monomer can be used alone, or two or more types can be used. Among these, multifunctional polymerizable monomers are preferred, especially when using photoforming methods.

[0155] There are no particular limitations on oligomers as long as they are compounds that are bonded to two or more of the aforementioned polymerizable monomers and have polymerizable properties.

[0156] Examples of monofunctional (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, erythritol mono(meth)acrylate, and other (meth)acrylates containing hydroxyl groups; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, etc. Alkyl methacrylates such as tert-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, lauryl methacrylate, cetyl methacrylate, and stearyl methacrylate; alicyclic methacrylates such as cyclohexyl methacrylate and isobornyl methacrylate; methacrylates containing aromatic groups such as benzyl methacrylate and phenyl methacrylate; and methacrylates with functional groups such as 2,3-dibromopropyl methacrylate, 3-methacryloyloxypropyltrimethoxysilane, and 11-methacryloyloxyundecyltrimethoxysilane.

[0157] Examples of monofunctional (meth)acrylamides include (meth)acrylamide, N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-di-n-propyl(meth)acrylamide, N,N-di-n-butyl(meth)acrylamide, N,N-di-n-hexyl(meth)acrylamide, N,N-di-n-octyl(meth)acrylamide, N,N-di-2-ethylhexyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and N,N-bis(2-hydroxyethyl)(meth)acrylamide.

[0158] Among these monofunctional polymerizable monomers, from the viewpoint of excellent polymerizability, (meth)acrylamide is preferred, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.

[0159] Examples of difunctional aromatic compounds include 2,2-bis((meth)acryloyloxyphenyl)propane, 2,2-bis[4-(2-hydroxy-3-acryloyloxy-2-hydroxypropoxy)phenyl]propane, 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (commonly known as "Bis-GMA"), 2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane, and 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane. Propane, 2,2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, 1,4-bis(2-(meth)acryloyloxyethyl)benzothionate, etc. (meth)acrylates. Among these, Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles. Among 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average molar number of ethoxy addition: 2.6, commonly referred to as "D-2.6E") is preferred.

[0160] Examples of difunctional aliphatic compounds include glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 2-ethyl-1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,2-bis(3-methacryloyloxy-2-hydroxypropoxy)ethane, and 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate (commonly known as "UDMA"), etc. Among these, from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles, triethylene glycol dimethacrylate (commonly known as "TEGDMA") and UDMA are preferred.

[0161] Examples of compounds with trifunctionality or higher include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxyl)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacetoxy-2,2,6,6-tetra(meth)acryloxymethyl-4-oxaheptane (meth)acrylates. Among these, from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxyl)propane-1,3-diol]tetramethacrylate and 1,7-diacetoxy-2,2,6,6-tetracetoxymethyl-4-oxaheptane are preferred.

[0162] In any of the methods described above, polymerization of the composition is preferably carried out using a polymerization initiator, and the composition preferably further comprises a polymerization initiator. The type of polymerization initiator is not particularly limited, but a photopolymerization initiator is particularly preferred. As a photopolymerization initiator, it can be appropriately selected from those commonly used in industry, with photopolymerization initiators used in dental applications being preferred. Specific examples of photopolymerization initiators are the same as those described above for the purpose of gel casting.

[0163] When manufacturing zirconia molded articles using a photoforming method with a zirconia composition, the specific method of photoforming is not particularly limited, and known methods can be appropriately used. For example, methods such as using a photoforming device to photopolymerize a liquid composition using ultraviolet light, laser, etc., thereby sequentially forming layers with the desired shape, and thus obtaining the zirconia molded article as the target.

[0164] To further increase the density of the zirconia molded body as a cured product, CIP treatment can be carried out after humidifying the zirconia molded body.

[0165] In the case of pressure molding, the powder containing zirconia particles can be humidified before pressure molding. The humidification method can be any known method without limitation; it can involve spraying water using a sprayer, or using a humidifier or a constant temperature and humidity device. The increase in moisture due to humidification depends on the average particle size of the contained zirconia particles, the average particle size of the stabilizer particles, etc., and is preferably more than 2% by mass, more preferably more than 3% by mass, further preferably more than 4% by mass, particularly preferably more than 5% by mass, and preferably 15% by mass or less, more preferably 13% by mass or less, and further preferably 11% by mass or less, relative to the mass of the powder before humidification and the molded body. It should be noted that the increase in moisture due to humidification can be calculated as a percentage by dividing the mass of the powder before humidification by the mass of the powder before humidification and the molded body (the mass of the powder after humidification and the molded body).

[0166] The pressure applied during CIP processing is the same as described above for the instructions on pressure molding.

[0167] (f) The process of stacking particles containing zirconium oxide particles and yttrium oxide particles. There are no particular limitations on the specific methods used to manufacture granules containing zirconium oxide and yttrium oxide particles. For example, a method can be used to dry the slurry using a spray dryer to produce granules, which can then be used for powder lamination molding.

[0168] There are no particular limitations on the powder lamination method, and examples include powder layering, SLS (Selective Laser Sintering), SLM (Selective Laser Melting), electron beam lamination, arc discharge lamination, and binder spraying. Regarding a better method that does not contain organic matter during lamination, it is preferable that organic matter is not used in the particle manufacturing stage.

[0169] Next, the zirconia pre-fired body of the present invention is obtained by pre-firing the molded body.

[0170] From the viewpoint that the use of the specific zirconium oxide composition described above ensures a reliable semi-sintered state, the pre-firing temperature (maximum pre-firing temperature) in the pre-firing process is preferably 600°C or higher, more preferably 700°C or higher, even more preferably 800°C or higher, and particularly preferably 850°C or higher.

[0171] Furthermore, from the viewpoint of ensuring processability, the preheating temperature is preferably below 1200°C, more preferably below 1150°C, even more preferably below 1100°C, and particularly preferably below 1050°C.

[0172] That is, the preferred temperature for manufacturing the zirconia pre-fired body of the present invention is 600~1200°C.

[0173] Furthermore, by using the zirconia composition obtained through the aforementioned pulverization process, the target zirconia pre-burnt body can be obtained even in regions with lower temperatures than before (e.g., around 600 to 900°C).

[0174] Regarding the holding time (residual time) at the aforementioned maximum pre-sintering temperature, there are no particular limitations as long as a semi-sintered state can be formed and a zirconia pre-sintered body with a half-value width within a specified range can be obtained. It is preferable to hold at the maximum pre-sintering temperature for 30 minutes to 6 hours.

[0175] In addition, the heating rate up to the maximum preheating temperature and the cooling rate from the maximum preheating temperature are preferably 300°C / min or less.

[0176] In a suitable embodiment, the heating rate for raising the zirconia molded body of the present invention to the highest pre-firing temperature during pre-firing is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, even more preferably 0.5°C / min or more, and preferably 50°C / min or less, more preferably 30°C / min or less, even more preferably 20°C / min or less.

[0177] By setting the heating rate above or below the aforementioned lower limit, productivity is increased. Furthermore, by setting the heating rate below or below the aforementioned upper limit, the volume difference between the interior and exterior of the zirconia molded body and / or the zirconia pre-sintered body can be suppressed. Additionally, in the case where the zirconia molded body contains organic matter, the rapid decomposition of that organic matter can be suppressed, thereby preventing cracking and / or damage.

[0178] [Zirconium oxide sintered body] Next, the sintered zirconia body will be described.

[0179] Zirconia sintered body is obtained by calcining the zirconia pre-sintered body obtained by the operation as described above.

[0180] The content of stabilizer (suitably yttrium oxide) in the zirconia sintered body of the present invention is the same as the content of stabilizer in the zirconia pre-sintered body.

[0181] The zirconia sintered body of the present invention has excellent light transmittance (linear light transmittance and total light transmittance) because the half-width of the main peak of the zirconia derived from the monoclinic crystal system in the zirconia pre-sintered body is within a specific range, and the zirconia sintered body produced by calcination at the highest sintering temperature (e.g., 1550°C) with a residence time (holding time) of less than 10 minutes is also excellent.

[0182] Therefore, the zirconia sintered body of the present invention can maintain the same level of high light transmittance as that of long-term sintering (e.g., holding time of 2 hours at the highest sintering temperature) after sintering for a short time of less than 10 minutes at the highest sintering temperature.

[0183] The zirconia sintered body of the present invention may contain a fluorescent agent. The fluorescent agent is the same as that in the zirconia pre-sintered body.

[0184] In this specification, regarding fluorescent agents, "100% by mass of zirconium oxide contained in the pre-sintered zirconium oxide body" can be understood as "100% by mass of zirconium oxide contained in the sintered zirconium oxide body".

[0185] The zirconia sintered body of the present invention may contain a colorant. Examples of colorants include those used in the zirconia pre-sintered body.

[0186] The content of colorant in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of colorant and the intended use of the zirconia sintered body. From the viewpoint of preferably using it as a dental patch, the content is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, based on the conversion of oxides of metal elements contained in the colorant, relative to 100% by mass of zirconia contained in the zirconia sintered body. In addition, the content of colorant, based on the conversion of oxides of metal elements contained in the colorant, is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, can be 0.1% by mass or less, and further can be 0.05% by mass or less.

[0187] To adjust the light transmittance of the zirconia sintered body of the present invention, the zirconia sintered body of the present invention may contain a light transmittance modifier. Examples of light transmittance modifiers include substances identical to those used in the zirconia pre-sintered body.

[0188] The content of the light transmittance modifier in the zirconia sintered body is not particularly limited, and can be appropriately adjusted according to the type of light transmittance modifier and the intended use of the zirconia sintered body. From the viewpoint that it can be preferably used as a dental patch, the content is preferably 0.1% by mass or less relative to 100% by mass of zirconia contained in the zirconia sintered body.

[0189] [Method for manufacturing zirconia sintered bodies] As a method for manufacturing the zirconia sintered body of the present invention, a method for manufacturing the zirconia sintered body by calcining the aforementioned zirconia pre-sintered body can be listed.

[0190] The preferred manufacturing method includes a step of calcining the aforementioned zirconia pre-sintered body under normal pressure at a maximum sintering temperature exceeding 1200°C and below 1650°C.

[0191] The zirconia pre-sintered body of the present invention, by being within the range of the aforementioned specified half-value width, can easily produce a zirconia sintered body of the present invention with excellent light transmittance, for example, even after sintering at a short time of less than 10 minutes at the highest sintering temperature.

[0192] When the zirconia pre-burnt body of the present invention is calcined to produce a sintered body, the maximum sintering temperature is preferably a condition that balances the light transmittance and mechanical strength of the zirconia sintered body.

[0193] Based on the above viewpoints, and considering the ease with which the desired zirconia sintered body can be obtained under normal pressure, the maximum sintering temperature is preferably above 1200°C, more preferably above 1250°C, and even more preferably above 1300°C. Furthermore, the maximum sintering temperature is preferably below 1650°C, more preferably below 1600°C, even more preferably below 1550°C, particularly preferably below 1500°C, and most preferably below 1450°C.

[0194] As one embodiment, from the viewpoint that by increasing the half-value width, calcination can be carried out at a lower temperature than before, a method for manufacturing a zirconia sintered body can be cited, which includes a process of calcination at a maximum sintering temperature of more than 1200°C and below 1450°C.

[0195] As another embodiment, a method for manufacturing a zirconia sintered body is provided, which includes a calcination process with a maximum sintering temperature of more than 1450°C and less than 1650°C, including a range with a small half-value width (e.g., more than 0.18° and less than 0.25°).

[0196] By setting the maximum sintering temperature above the aforementioned lower limit and below the aforementioned upper limit, sintering can be performed sufficiently, and a dense sintered body can be easily obtained. Furthermore, by setting the maximum sintering temperature below the aforementioned upper limit, the deactivation of the fluorescent agent can be suppressed.

[0197] The holding time at the highest sintering temperature is preferably 15 minutes or more, more preferably 30 minutes or more, and even more preferably 40 minutes or more. Furthermore, it is preferably 20 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less.

[0198] When a sintered body is manufactured by sintering for a short time, if the holding time at the highest sintering temperature is 10 minutes or less, the sintering time is not particularly limited. From the perspective of being able to obtain the desired zirconia sintered body efficiently and stably with good productivity, the holding time at the highest sintering temperature is preferably 10 minutes or less, more preferably 5 minutes or less, further preferably 3 minutes or less, and particularly preferably 2 minutes or less.

[0199] The holding time can be set to 30 seconds or more, 45 seconds or more, or 1 minute or more.

[0200] The light transmittance of the zirconia sintered body is not reduced during manufacturing, and the calcination time for manufacturing the sintered body can be shortened. In particular, the holding time at the highest sintering temperature for manufacturing the sintered body can be shortened to less than 10 minutes. This improves production efficiency. When the zirconia pre-sintered body of the present invention is applied to dental articles, the size of the dental article used for treatment can be determined, the time from machining to the point where the dental article can be used for treatment can be shortened, and the time burden on patients can be reduced. Furthermore, energy costs can be reduced.

[0201] The heating and cooling rates in the calcination process are preferably set in a way that minimizes the time required for the calcination process. For example, the heating rate can be set according to the performance of the calcination furnace to reach the highest sintering temperature in the shortest possible time. The heating rate up to the highest sintering temperature can be set to, for example, 10°C / min or higher, 50°C / min or higher, 100°C / min or higher, 120°C / min or higher, 150°C / min or higher, 200°C / min or higher, 250°C / min or higher, 300°C / min or higher, or 350°C / min or higher. The cooling rate is preferably set at a rate that prevents defects such as cracks from forming in the sintered body. For example, the sintered body can be allowed to cool naturally at room temperature after heating.

[0202] The pre-calcination and calcination in this invention can be carried out using a calcination furnace. There is no particular limitation on the type of calcination furnace; for example, electric furnaces and degreasing furnaces commonly used in industry can be used.

[0203] Commercially available dental calcining furnaces (such as the trade name "Sintra CS" (manufactured by Shenpaz)) can be used.

[0204] The zirconia sintered body of the present invention can be manufactured even without HIP treatment. As an optional step, HIP treatment can be performed after sintering at atmospheric pressure to further improve light transmittance and mechanical strength.

[0205] Hereinafter, the sintered body obtained by sintering at the aforementioned highest sintering temperature (the sintered body before HIP treatment) will be referred to as the "primary sintered body", and the sintered body after HIP treatment will be referred to as the "HIP-treated sintered body".

[0206] HIP processing can be performed using a known hot isostatic pressing (HIP) apparatus.

[0207] When performing HIP treatment on a single-stage sintered body, the HIP pressure is not particularly limited. However, to obtain a dense sintered body with high mechanical strength, the HIP pressure is preferably 100 MPa or higher, more preferably 125 MPa or higher, and even more preferably 130 MPa or higher. Furthermore, the upper limit of the HIP pressure is not particularly limited; for example, it can be set to 400 MPa or lower, 300 MPa or lower, or even 200 MPa or lower.

[0208] When performing HIP treatment on the aforementioned primary sintered body, the heating rate is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more. Furthermore, the heating rate is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. By setting the heating rate to the aforementioned lower limit or above, productivity will be improved.

[0209] When performing HIP treatment on the aforementioned sintered body, the HIP time (the time to maintain the highest pressure and temperature) is not particularly limited. However, to obtain a dense zirconia sintered body with high mechanical strength, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. In addition, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0210] In the method for manufacturing zirconia sintered bodies of the present invention, when performing HIP treatment on the aforementioned primary sintered body, the pressure medium is not particularly limited. From the viewpoint of minimizing the impact on zirconia, the pressure medium can be selected from at least one of oxygen, oxygen containing 3% hydrogen, air, and inactive gases (such as nitrogen, argon, etc.).

[0211] When performing HIP treatment on the aforementioned primary sintered body under an oxygen-mixed gas atmosphere, the oxygen concentration is not particularly limited; for example, it can be set to be greater than 0% and less than 20%.

[0212] When using an oxygen-mixed gas, at least one of the following inert gases (such as nitrogen, argon, etc.) can be selected as the gas other than oxygen.

[0213] During the aforementioned HIP treatment, if an inert gas or the like is used in a reducing atmosphere, blackening may sometimes occur due to oxygen deficiency. In this case, to remove the blackening, it is preferable to include a heat treatment process (hereinafter also referred to as "tempering") at 1650°C or below in the atmosphere or in an oxygen-excess atmosphere after the aforementioned HIP treatment. From the viewpoint of effectively performing the heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere.

[0214] An atmosphere with excess oxygen refers to an atmosphere where the oxygen concentration is higher than that in the atmosphere.

[0215] As an oxygen-excess atmosphere, there is no particular limitation as long as the oxygen concentration exceeds 21% and is less than 100%, and it can be appropriately selected from this range. For example, the oxygen concentration can be set to 100%. During the aforementioned HIP treatment, if an inert gas or the like is used in a reducing atmosphere, blackening may sometimes occur due to oxygen deficiency. In this case, to remove the blackening, it is preferable to include a heat treatment process (hereinafter also referred to as "tempering") at 1650°C or below in the atmosphere or an oxygen-excess atmosphere after the aforementioned HIP treatment step. From the viewpoint of effectively performing the heat treatment, it is more preferable to perform it in an oxygen-excess atmosphere. An oxygen-excess atmosphere refers to an oxygen concentration higher than that in the atmosphere. As an oxygen-excess atmosphere, there is no particular limitation as long as the oxygen concentration exceeds 21% and is less than 100%, and it can be appropriately selected from this range. For example, the oxygen concentration can be set to 100%.

[0216] The zirconia sintered body of the present invention is not particularly limited as long as it achieves the effects of the present invention. It can be a single sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment.

[0217] Depending on the aesthetic appeal of the zirconia sintered body (e.g., the color of dental repairs), the heat treatment temperature in the atmosphere or in an oxygen-rich atmosphere can be appropriately changed.

[0218] In a suitable embodiment, from the viewpoint of the aesthetics of the zirconia sintered body, the heat treatment temperature in the atmosphere or in an oxygen-excess atmosphere is preferably below 1650°C, more preferably below 1600°C, and even more preferably below 1550°C.

[0219] In other suitable embodiments, from the viewpoint of the aesthetics of the zirconia sintered body, the heat treatment temperature in the atmosphere or in an oxygen-excess atmosphere is preferably below 1400°C, more preferably below 1300°C, and even more preferably below 1200°C.

[0220] Furthermore, in any embodiment, the heat treatment temperature is preferably 500°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher.

[0221] The aforementioned tempering process can be performed using a standard dental zirconia calcination furnace. Commercially available zirconia calcination furnaces can be used. Examples of commercially available furnaces include Noritake KATANA (registered trademark) F-1, F-1N, F-2, and F-2N (all from SK Medical Electronics Co., Ltd.).

[0222] The zirconia sintered body obtained by calcining the zirconia pre-burnt body of the present invention is suitable for use in dental products.

[0223] Examples of dental products include, for example, inner crowns, frameworks, dental crowns, dental bridges, bridge abutments, implants, implant screws, implant fixation devices, implant bridges, implant bars, dental crowns, dentures, inlays, onlays, orthodontic wires, and veneers.

[0224] By using the zirconia pre-fired body of the present invention in components such as implant screws and implant fixation devices, gingival discoloration caused by metal can be suppressed when using metal materials, resulting in excellent aesthetics.

[0225] Furthermore, as for their manufacturing methods, appropriate methods can be selected according to various applications. For example, dental articles can be obtained by machining the zirconia pre-fired body of the present invention followed by calcination. It should be noted that a CAD / CAM system is preferably used in this machining process.

[0226] As a CAD / CAM system, there are no particular limitations, and any known device may be used. Examples of known devices include, for instance, CAD / CAM systems such as "KATANA (registered trademark) CAD / CAM system" and those manufactured by Kuraray Noritake Dental Co., Ltd.

[0227] As long as the present invention achieves the effects of the present invention, it includes embodiments obtained by combining all or part of the above-described structures in various ways within the scope of the technical concept of the present invention. Example

[0228] Next, embodiments are listed to illustrate the present invention in more detail. However, the present invention is not limited to these embodiments at all, and those skilled in the art can make various modifications within the scope of the technical concept of the present invention.

[0229] [Example 1] Commercially available zirconium oxide powder (Y2O3: 0 mol%) and commercially available yttrium oxide powder were added to water. They and zirconium oxide pulverizing media (diameter: 0.1 mm) were then added to the container of a bead mill. The pulverization time was set to 1 hour, and the bead mill was used to pulverize the material to obtain a slurry (average particle size: below 0.2 μm).

[0230] Next, an organic binder is added to the resulting slurry and mixed. The mixed slurry is then dried and granulated using a spray dryer to obtain powder.

[0231] The powder is fed into a cylindrical mold and uniaxially pressed at 33 MPa. Then, it undergoes CIP treatment at 190 MPa to obtain a plate-shaped or disc-shaped molded body.

[0232] The resulting molded body was placed in an electric furnace and heated from room temperature at a rate of 10°C / min. It was then held at 500°C for 2 hours to degrease the organic components. Subsequently, the temperature was increased at a rate of 10°C / min and held at 875°C for 2 hours. Finally, it was slowly cooled at a rate of -10°C / min to obtain a zirconia pre-fired body.

[0233] Furthermore, the pre-sintered zirconia body was calcined under atmospheric pressure, a heating rate of 10℃ / min, a maximum sintering temperature of 1375℃, and a holding time of 2 hours to obtain a sintered zirconia body containing 4.5 mol% yttrium oxide. The resulting sintered zirconia body was white.

[0234] [Examples 2-14 and Comparative Examples 1-3] In Comparative Examples 1-3, the highest sintering temperature was changed to 1550°C, and the conditions were changed to those described in Table 2. Otherwise, the zirconia pre-sintered body and zirconia sintered body were manufactured using the same method as in Example 1.

[0235] In Examples 2-14, the conditions were changed to those described in Table 2. Otherwise, the zirconia pre-fired body and zirconia sintered body were manufactured using the same method as in Example 1.

[0236] For example, regarding the yttrium oxide content, the amount used was varied in Examples 4-5 and Comparative Examples 1-2 so that the yttrium oxide content was the amount listed in Table 2. In Examples 2-5 and Comparative Examples 1-3, the same substances as in Example 1 were used for the zirconium oxide raw material (zirconia powder) and the yttrium oxide raw material (yttrium oxide powder).

[0237] In Comparative Examples 1-3, the pulverization process was changed to use a ball mill with zirconia balls of 2 mm diameter in the pulverizing medium instead of a bead mill, and the pulverization time was changed to that described in Table 2.

[0238] In Examples 10 and 11, regarding the pulverization process, after pulverization in the same ball mill as in Example 1, pulverization was performed using zirconia pulverizing media with a diameter of 0.1 mm and a bead mill, and the pulverization time for each was changed to the pulverization time recorded in Table 2.

[0239] In Example 12, instead of commercially available zirconium oxide powder (Y2O3: 0 mol%), 1.5Y zirconium oxide (Y2O3: 1.5 mol%) was used, and the yttrium oxide content was adjusted to that shown in Table 2.

[0240] In Example 13, instead of commercially available zirconium oxide powder (Y2O3: 0 mol%) and commercially available yttrium oxide powder, 1.5Y zirconium oxide (Y2O3: 1.5 mol%) and 40Y zirconium oxide (Y2O3: 40 mol%) were used, and the yttrium oxide content was adjusted to the levels described in Table 2.

[0241] In Example 14, instead of commercially available yttrium oxide powder, 40Y zirconium oxide (Y2O3: 40mol%) was used and adjusted to the yttrium oxide content described in Table 2.

[0242] It should be noted that 1.5Y zirconium oxide (Y2O3: 1.5 mol%) is manufactured as follows.

[0243] Commercially available zirconium oxide powder (Y₂O₃: 0 mol%) and commercially available yttrium oxide powder were added to water at a yttrium oxide molar percentage of 1.5 mol% relative to the total molar percentage of zirconium oxide and yttrium oxide. These powders, along with zirconium oxide pulverizing media (diameter: 2 mm), were fed into the container of a ball mill, and the pulverization process was performed for 48 hours to obtain a slurry (average particle size: below 0.2 μm). The slurry was then dried and granulated using a spray dryer to obtain a powder. Subsequently, the powder was heated and held at 1000°C for 100 hours as a raw material.

[0244] In addition, 40Y zirconium oxide (Y2O3: 40mol%) is manufactured as follows.

[0245] Commercially available zirconium oxide powder (Y₂O₃: 0 mol%) and commercially available yttrium oxide powder were added to water at a yttrium oxide mol% relative to the total yttrium oxide and zirconium oxide mol%. These powders, along with zirconium oxide pulverizing media (diameter: 2 mm), were fed into the container of a ball mill, and the pulverization process was carried out for 48 hours to obtain a slurry (average particle size: below 0.2 μm). The slurry was then dried and granulated using a spray dryer to obtain a powder. Subsequently, the powder was heated and held at 1000°C for 100 hours as a raw material.

[0246] [Example 6] For Example 6, the heating rate was changed to 350°C / min, the maximum sintering temperature to 1580°C, and the holding time at the maximum sintering temperature was changed to 2 minutes. Regarding the pulverization process, a ball mill using 2mm diameter zirconia balls in the pulverizing medium was used, and the pulverization time was changed to that described in Table 2. Otherwise, the zirconia pre-sintered body and zirconia sintered body were manufactured using the same method as in Example 1. In Example 6, the zirconia raw material (zirconia powder) and yttrium oxide raw material (yttrium oxide powder) were the same substances used as in Example 1.

[0247] <Evaluation of the half-width of monoclinic crystals in zirconia pre-sintered bodies> The half-width of the main peak of the zirconia pre-sintered body obtained in each embodiment and comparative example, originating from the monoclinic crystal system, was determined by analytical analysis of the crystal system in the zirconia pre-sintered body.

[0248] Specifically, regarding X-ray diffraction, using a fully automated horizontal multi-object X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and integrated X-ray analysis software (SmartLab Studio II, manufactured by Rigaku Corporation), measurements were performed under the following conditions to determine the half-width (in °) of the peak near 2θ = 28.2° at the apex of the main peak of the monoclinic crystal system. X-ray source: Cu Kα (λ=1.54186Å) Goniometer length: 300mm Optical system: lumped method Detector: High-speed one-dimensional X-ray detector (D / teX Ultra250) Monochromatic: Kβ filter Tube voltage: 40kV Tube current: 30mA Scan axis: 2θ / θ Scanning speed: 0.2° / minute Sampling procedure: 0.01°.

[0249] Evaluation of the Prevalence of Zirconia Pre-sintered Materials in Crystal Systems The presence rate f of unsolvable yttrium oxide in the zirconia pre-sintered bodies obtained in each embodiment and comparative example y , tetragonal crystallinity f t cubic crystallinity f c and monoclinic crystallization rate f m The crystal system was determined by analyzing the zirconia pre-sintered body.

[0250] Specifically, regarding X-ray diffraction, a fully automated horizontal multi-object X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and X-ray analysis software (SmartLab Studio II, manufactured by Rigaku Corporation) were used to perform measurements under the following conditions to determine the area intensity (peak area intensity I) of each peak. X-ray source: Cu Kα (λ=1.54186Å) Goniometer length: 300mm Optical system: lumped method Detector: High-speed one-dimensional X-ray detector (D / teX Ultra250) Monochromatic: Kβ filter Tube voltage: 40kV Tube current: 30mA Scan axis: 2θ / θ Scanning speed: 0.2° / minute Sampling procedure: 0.01°.

[0251] Using the area intensity of each peak, the presence rate f of undissolved yttrium oxide is calculated according to equations (1-1) and (1-2) above. y (%) and monoclinic crystallinity f m (%). The results are shown in Table 2.

[0252] <Evaluation of the average primary particle size of zirconia pre-sintered body> In the zirconia pre-sintered bodies obtained in each embodiment and comparative example, images of the pre-sintered body surface were obtained using an ultra-high resolution field emission scanning electron microscope (trade name "SU8200", manufactured by Hitachi High Technology Co., Ltd.) with an accelerating voltage of 5.0 kV, a working distance of 8.7 mm, and a magnification of 100,000x. The average particle size of the image was calculated through image analysis.

[0253] In particle size measurement, image analysis software (trade name "Image-Pro Plus", manufactured by Hakuto Co., Ltd.) was used to binarize the acquired SEM image, adjust the brightness range to make the grain boundaries more distinct, and identify particles from the field of view (region). In the processing file where the primary particle size was identified, the "Diameter" option in the "Count / Size dialog box" was selected to calculate the distribution (n=4). Specifically, for the four fields of view of a single sample, the arithmetic mean of the average particle size (primary particle size) measured in each field of view using the aforementioned image analysis software was calculated.

[0254] <3-point bending strength> The three-point flexural strength of zirconia sintered bodies was determined according to ISO 6872:2015.

[0255] Samples measuring 4 mm × 1.2 mm × 15 mm were prepared from the plate-shaped zirconia sintered bodies of each embodiment and comparative example. The samples were measured using a universal testing machine under the conditions of a support distance of 12 mm and a crosshead speed of 0.5 mm / min (arithmetic mean of n=5).

[0256] The criteria for judging the flexural strength of zirconia sintered bodies are as described in Table 1 below.

[0257] [Table 1]

[0258] <Total light transmittance, linear light transmittance (1.0mm thickness)> The total light transmittance and linear light transmittance of the 1.0 mm thick zirconia sintered body were measured using a turbidimeter (Nippon Denshoku Kogyo Co., Ltd., "Haze Meter NDH 4000"), where light emitted from a light source was transmitted through the sample and scattered, and the results were measured using an integrating sphere (arithmetic mean of n=3). The measurements were performed according to ISO 13468-1:1996 and JIS K 7361-1:1997, with a D65 light source selected. The 30 mm diameter × 1.0 mm thick disc-shaped zirconia sintered body, mirror-polished on both sides, was used as the sample for the measurements.

[0259] In the table, the yttrium oxide content refers to the ratio (mol%) of the number of moles of yttrium oxide to the total number of moles of zirconium oxide and yttrium oxide.

[0260] In addition, in the table, 28.2° refers to the peak position of the monoclinic crystal system that was measured.

[0261] Based on the above results, it can be confirmed that the zirconia pre-sintered body of the present invention has excellent mechanical strength and light transmittance (linear light transmittance and total light transmittance).

[0262] Furthermore, the zirconia pre-sintered body of the present invention has high total light transmittance and excellent light transmission even when the thickness of the zirconia sintered body is 1.0 mm, thus exhibiting excellent aesthetics when manufacturing dental materials (e.g., dental repairs).

[0263] Furthermore, the results of Example 6 confirm that even when the holding time at the highest sintering temperature is 2 minutes, the light transmittance of the resulting zirconia sintered body is excellent.

[0264] In the comparative example, the half-width of the main peak originating from the monoclinic system was not within the desired range, and therefore the target physical property could not be obtained.

[0265] For example, it can be confirmed that the target mechanical strength could not be obtained in Comparative Example 3, but in Examples 10 and 11, an excellent mechanical strength of more than 270 MPa can be obtained compared with Comparative Example 3. The mechanical strength and light transmittance (linear light transmittance and total light transmittance) of the obtained zirconia sintered body are excellent.

[0266] Industrial utilization The zirconia pre-fired body of the present invention is useful for the manufacture of dental articles (especially dental articles used in dental hospital treatment).

Claims

1. A zirconia pre-sintered body comprising zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia. The aforementioned zirconium oxide includes monoclinic zirconium oxide. The half-width of the main peak originating from the aforementioned monoclinic crystal system in the powder X-ray diffraction pattern based on CuKα rays is greater than 0.18°.

2. The zirconia pre-fired body according to claim 1, wherein, The aforementioned stabilizer is yttrium oxide.

3. The zirconia pre-fired body according to claim 2, wherein, The presence rate f of yttrium oxide not dissolved in zirconium oxide, calculated using the following equation (1-1). y (%) less than 4%, f y (%)=I y / (I m +I t +I c +I y )×100 (1-1) In the formula, f y f represents the presence rate of yttrium oxide that is not dissolved in zirconium oxide. y (%), in XRD determination, I m This represents the area intensity of the peak near 2θ = 28.2° at the apex of the main peak in a monoclinic crystal system; I t This represents the area intensity of the peak near 2θ = 30.3° at the apex of the main peak of the tetragonal crystal system; I c I represents the area intensity of the peak near 2θ = 30.0° at the apex of the main peak in a cubic crystal system; y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak of yttrium oxide, which is not dissolved in zirconium oxide.

4. The zirconia pre-fired body according to claim 2 or 3, wherein, The monoclinic crystal ratio f calculated using the following equation (1-2) m (%) less than 55%, f m (%)=I m / (I m +I t +I c +I y )×100 (1-2) In the formula, f m Indicates the monoclinic crystallinity (%); in XRD measurements, I m This represents the area intensity of the peak near 2θ = 28.2° at the apex of the main peak in a monoclinic crystal system; I t This represents the area intensity of the peak near 2θ = 30.3° at the apex of the main peak of the tetragonal crystal system; I c I represents the area intensity of the peak near 2θ = 30.0° at the apex of the main peak in a cubic crystal system; y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak of yttrium oxide, which is not dissolved in zirconium oxide.

5. The zirconia pre-fired body according to claim 4, wherein, The aforementioned monoclinic crystal ratio f m (%) less than 50%.

6. The zirconia pre-fired body according to claim 1 or 2, wherein, The average primary particle size includes primary particles larger than 60 nm and smaller than 250 nm.

7. The zirconia pre-fired body according to claim 1 or 2, wherein, The content of the aforementioned stabilizer relative to the total molar of the aforementioned zirconium oxide and stabilizer is 2~10 mol.

8. A method for manufacturing the zirconia pre-fired body according to claim 1 or 2, comprising: A process for manufacturing a zirconia composition comprising zirconia particles and stabilizer particles capable of inhibiting the phase transformation of zirconia; The pulverization process for pulverizing the aforementioned zirconium oxide composition; A molding process for obtaining a molded article by molding a pulverized zirconium oxide composition; and The pre-firing process for pre-firing the aforementioned molded body. The aforementioned zirconia particles include monoclinic zirconia particles. In the aforementioned pulverizing process, (i) a pulverizing medium with a diameter of less than 1 mm is used and the pulverizing time is more than 10 minutes, or (ii) a pulverizing medium with a diameter of more than 1 mm is used and the pulverizing time exceeds 40 hours.

9. The method for manufacturing a zirconia pre-fired body according to claim 8, wherein, The pre-firing temperature in the aforementioned pre-firing process is 600~1200℃.

10. A method for manufacturing zirconia sintered bodies, wherein, The zirconia pre-sintered body according to claim 1 or 2 is calcined under normal pressure at a maximum sintering temperature exceeding 1200°C and below 1650°C.

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