Zirconium oxide presintered body and method for producing same

Abstract

Provided are: a zirconia pre-sintered body which exhibits excellent light transmittance even when the holding time at the maximum sintering temperature is 2 minutes; and a method for producing the zirconia pre-sintered body. The present invention relates to a zirconia presintered body which contains zirconia and yttrium oxide as components, and which contains Y4Zr3O12 as a crystal system. It is preferable that the presence rate fd (%) of Y4Zr3O12 as calculated by formula (1-1) is 2.5% or more as the zirconia pre-sintered body. Fd (%) = Id / (Im + It + Ic + Iy + Id) * 100 (1-1). (In the formula, the description of symbols is omitted)

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 that exhibit excellent light transmittance even when held at the highest sintering temperature for a duration of 2 minutes, 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] In the past, dental labs often used only zirconium oxide to make dental fillings. As a result, patients could not receive dental fillings on the same day of their dental appointment and had to schedule a follow-up visit to receive them.

[0006] In response, a treatment method has been proposed that allows dental fillings to be easily fabricated at a dental hospital, enabling treatment with dental fillings during a single visit (One Visit Treatment). In this case, zirconia needs to be calcined within a short period of time, as proposed in Patent Document 1, etc.

[0007] Existing technical documents Patent documents Patent document 1: International Publication No. 2018 / 056330. Summary of the Invention

[0008] The problem the invention aims to solve Patent Document 1 shows that a sintered body prepared by calcining a pre-calcined body at a maximum sintering temperature of 1550°C for 15 minutes can also achieve the same light transmittance as that prepared by calcining at the same temperature for 120 minutes. This demonstrates that it can shorten the calcination time.

[0009] However, it is clear from the present inventors that in the invention described in Patent Document 1, if the holding time at the highest sintering temperature of 1550°C is further shortened (for example, to 7 minutes or less), the light transmittance will decrease. Therefore, it is understood that in the invention described in Patent Document 1, there is room for improvement in order to further shorten the holding time.

[0010] The purpose of this invention is to provide a zirconia pre-sintered body with excellent light transmittance even when the holding time is 2 minutes at the highest sintering temperature, and a method for manufacturing the same.

[0011] In addition, another object of the present invention is to provide a zirconia sintered body with excellent light transmittance even when using a manufacturing method that holds the zirconia pre-sintered body at the highest sintering temperature for 2 minutes.

[0012] means for solving problems In order to solve the above-mentioned problems, the inventors have repeatedly conducted in-depth research and found that by preparing a solution containing zirconium oxide, yttrium oxide and Y4Zr3O as a crystal system... 12 The zirconia pre-sintered body exhibits excellent light transmittance even when held at the highest sintering temperature for 2 minutes. Based on this insight, further research was conducted, and the present invention was completed.

[0013] The present invention includes the following technical solutions.

[0014] [1] Zirconia pre-sintered body, comprising zirconium oxide, yttrium oxide, and Y4Zr3O as a crystal system. 12 .

[0015] [2] According to the zirconia pre-fired body described in [1], the Y4Zr3O calculated using the following formula (1-1) 12 Presence rate f d (%) is above 2.5%.

[0016] f d (%) = I d / (I m +I t +I c +I y +I d )×100 (1-1) (where f) d Y4Zr3O 12 Presence rate (%); 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; d This indicates the presence of Y4Zr3O 12 The area intensity of the peak near 2θ=29.6° at the summit of the main peak; I y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak where unsolidified yttrium oxide appears.

[0017] It should be noted that, due to Y4Zr3O 12 Since the main peaks of the tetragonal and cubic crystal systems are located close to each other, peak separation is used to calculate the area intensity of each main peak. [3] According to the zirconia pre-fired body described in [1] or [2], wherein the aforementioned zirconia comprises monoclinic zirconia, the monoclinic crystal ratio f calculated using the following formula (1-2) is... m (%) Less than 55%.

[0018] f m (%) = I m / (I m +I t +I c +I y +I d )×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; d This indicates the presence of Y4Zr3O 12 The area intensity of the peak near 2θ=29.6° at the summit of the main peak; I y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak where unsolidified yttrium oxide appears.

[0019] It should be noted that, due to Y4Zr3O 12Since the main peaks of the tetragonal and cubic crystal systems are located close to each other, peak separation is used to calculate the area intensity of each main peak. [4] The zirconia pre-burnt body according to any one of [1] to [3], wherein the content of yttrium oxide is 2.5 mol% or more and 10 mol% or less relative to the total molar content of zirconia and yttrium oxide.

[0020] [5] Zirconia pre-fired body, comprising zirconium oxide and yttrium oxide, When comparing the first translucency of a first sintered body prepared by calcining the aforementioned zirconia pre-sintered body at 1550°C for 7 minutes at a heating rate of 350°C / min with the second translucency of a second sintered body prepared by calcining the aforementioned zirconia pre-sintered body at 1550°C for 120 minutes at a heating rate of 10°C / min, The aforementioned first light transmittance is more than 85% of the aforementioned second light transmittance.

[0021] [6] A method for manufacturing a zirconia pre-fired body according to any one of [1] to [5], comprising: A process for manufacturing a zirconium oxide composition comprising zirconium oxide particles and yttrium oxide particles; A pulverizing 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. 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.

[0022] [7] According to the method for manufacturing zirconia pre-fired body described in [6], the pre-firing temperature in the aforementioned pre-firing process is 600~1300℃.

[0023] [8] A zirconia sintered body comprising zirconia and a stabilizer capable of suppressing the zirconia phase transformation, wherein at least one zirconia crystal grain in the aforementioned zirconia sintered body has a portion having a concentration gradient of the aforementioned stabilizer in the same crystal grain that gradually decreases from the center side of the grain toward the grain boundary.

[0024] [9] According to the zirconia sintered body described in [8], wherein the aforementioned concentration gradient is 0.1 to 3 mol relative to the total molar of zirconia and stabilizer.

[0025]

[10] The zirconia sintered body according to [8] or [9], wherein the aforementioned stabilizer capable of suppressing the zirconia phase transformation is yttrium oxide.

[0026]

[11] A zirconia sintered body comprising zirconia and a stabilizer capable of inhibiting the zirconia phase transformation, wherein the aforementioned zirconia sintered body comprises: The aforementioned stabilizer content is 4-6 mol% (L) of zirconia crystalline particles relative to the total molar percentage of zirconia and stabilizer; and The aforementioned stabilizer content is 1~3 mol% of the total molar content of zirconium oxide and stabilizer in zirconium oxide crystal particles (S).

[0027]

[12] According to the zirconia sintered body described in

[11] , wherein the average grain diameter of the aforementioned zirconia crystal particles (L) is in the range of 0.5 to 2.0 μm. The average grain diameter of the aforementioned zirconia crystal particles (S) is in the range of 0.1~0.3 μm.

[0028]

[13] The zirconia sintered body according to

[11] or

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

[0029] Invention Effects According to the present invention, a zirconia pre-sintered body and a method thereof are provided that exhibit excellent light transmittance even when the holding time is 2 minutes at the highest sintering temperature.

[0030] Furthermore, by using the zirconia pre-sintered body and zirconia composition of the present invention, and their manufacturing method, it is possible to obtain a zirconia sintered body that maintains the same level of high translucency as that of a long-term sintered body after short-time sintering at 1550°C for a holding time of less than 7 minutes. This contributes to further improvements in productivity, such as reducing treatment time in dental hospitals, and is advantageous for achieving single-visit treatment in dental hospitals.

[0031] Furthermore, by using the zirconia pre-sintered body and zirconia composition of the present invention, as well as their manufacturing methods, it is possible to obtain zirconia sintered bodies with excellent mechanical strength and light transmittance at a lower maximum sintering temperature than before (e.g., below 1450°C).

[0032] Furthermore, the present invention provides a zirconia sintered body with excellent light transmittance by using a manufacturing method that holds the zirconia pre-sintered body at the highest sintering temperature for 2 minutes during calcination.

[0033] Furthermore, through this invention, a manufacturing method that holds the zirconia pre-sintered body at the highest sintering temperature for 2 minutes during calcination can also provide a zirconia sintered body with excellent mechanical strength. Attached Figure Description

[0034] Figure 1It is an electron beam diffraction image used to illustrate the method for calculating the distance and angle of diffraction points.

[0035] Figure 2 The results were obtained by observing the zirconia sintered body described in this invention using a transmission electron microscope (TEM). Detailed Implementation

[0036] [Zirconium oxide pre-fired body] The zirconia pre-calcined body of the present invention comprises zirconia, yttrium oxide, and Y4Zr3O as a crystal system. 12 In other words, the present invention relates to zirconia pre-sintered bodies, which are zirconia pre-sintered bodies comprising zirconia and yttrium oxide as components, and containing Y4Zr3O. 12 As a crystal system.

[0037] In this manual, "Y4Zr3O" 12 "Y4Zr3O" refers to the metastable crystal system of zirconium oxide present in the sintered zirconium oxide body. 12 It exists in the phase diagram up to around 1375℃.

[0038] In this specification, "zirconia composition" refers to a composition containing zirconia powder and yttrium oxide powder.

[0039] 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.

[0040] 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.

[0041] 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%.

[0042] 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, the terms "zirconia," "zirconia particles," and "zirconia powder" refer to substances containing both ZrO2 and HfO2. Additionally, yttrium oxide dissolved in zirconia particles and / or powders are also included in "zirconia particles" and "zirconia powder," respectively.

[0043] In this instruction manual, "atmospheric pressure" refers to standard atmospheric pressure (1 atm).

[0044] 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.

[0045] As a suitable implementation method, Y4Zr3O calculated using the following formula (1-1) can be listed. 12 Presence rate f d (%) is 2.5% or more of the zirconia pre-fired body.

[0046] f d (%) = I d / (I m +I t +I c +I y +I d )×100 (1-1) (where f) d Y4Zr3O 12 Presence rate (%), 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; d This indicates the presence of Y4Zr3O 12 The area intensity of the peak near 2θ=29.6° at the summit of the main peak; I y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak where unsolidified yttrium oxide appears.

[0047] It should be noted that, due to Y4Zr3O 12 Since the main peaks of the tetragonal and cubic crystal systems are located close to each other, peak separation is used to calculate the area intensity of each main peak. Y4Zr3O in the zirconia pre-fired body described in the aforementioned suitable embodiments 12 Presence rate f dThe percentage (%) is preferably 3.0% or more, more preferably 4.0% or more, further preferably 5.0% or more, and particularly preferably 6.0% or more. From the viewpoint that the zirconia sintered body obtained even with a holding time of 2 minutes at the highest sintering temperature has excellent light transmittance, or that it easily maintains the same level of high light transmittance as long-sintered bodies after short-time sintering at 1550°C with a holding time of 7 minutes or less, the most preferred percentage is 6.5% or more. Furthermore, from the viewpoint that Y4Zr3O 12 Based on the viewpoint that the phase transformation to other crystal systems is in a rate-controlled stage and that zirconia pre-sintered bodies are not suitable for sintering, the aforementioned Y4Zr3O 12 Presence rate f d The percentage (%) is preferably 30% or less, more preferably 25% or less, further preferably 22% or less, and especially preferably 20% or less.

[0048] Y4Zr3O 12 Presence rate f d The percentage can be calculated using the formula (1-1) above.

[0049] Y4Zr3O 12 Presence rate f d The determination method for (%) is as described in the examples described below.

[0050] The zirconia pre-fired body of the present invention comprises Y4Zr3O 12 As a crystal system (particularly suitable for: existence rate f) d (%) is a specified ratio), so the reason why the light transmittance of the zirconia sintered body is excellent even when the holding time is 2 minutes at the highest sintering temperature, and the reason why the same high light transmittance can be maintained after short-time sintering at 1550°C with a holding time of less than 7 minutes as that of long-time sintering, is still uncertain, but can be speculated as follows.

[0051] It can be considered that in the zirconia pre-sintered body, the inclusion of Y4Zr3O 12 This reduces the degree of yttrium atom pre-sintering, making the pre-sintered body closer to the final state of yttrium atoms in the sintered body. Consequently, the distance that yttrium atoms need to move toward the zirconium oxide side during calcination is shortened. As a result, the heat energy required for calcination is reduced. Compared with existing technologies, even with calcination in a shorter time, a sintered body with the same degree of light transmittance can be obtained.

[0052] The zirconia pre-sintered body contains yttrium oxide (Y₂O₃) as a stabilizer to inhibit the zirconia phase transformation. In this specification, the yttrium oxide included as a component in the zirconia pre-sintered body does not necessarily need to exist in the form of Y₂O₃ monomer; it can also exist in a state containing yttrium element (e.g., Y₄Zr₃O₃). 12Yttrium oxide may exist in the form of Y2O3 crystals, and therefore does not necessarily need to be detected in the form of Y2O3 crystals.

[0053] The yttrium oxide content in the zirconia pre-sintered body is preferably 2.5 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 (zirconia (IV); ZrO2) and yttrium oxide. From the viewpoint that 2.5 mol% or more increases the cubic crystal system within the sintered body and improves light transmittance, this is preferable.

[0054] Furthermore, the yttrium oxide content is preferably 10 mol% or less, more preferably 9.0 mol% or less, even more preferably 8.5 mol% or less, and particularly preferably 8.0 mol% or less. When the yttrium oxide content is 10 mol% or less, it is preferable from the viewpoint of preventing a decrease in mechanical strength. The stabilizer content of the zirconia pre-sintered body of the present invention can be determined by, for example, inductively coupled plasma (ICP) luminescence spectrophotometry or fluorescence X-ray analysis.

[0055] In the zirconia pre-calcined body of the present invention, the stabilizer capable of inhibiting the zirconia phase transformation may be only yttrium oxide, or may also include stabilizers other than yttrium oxide capable of inhibiting the zirconia phase transformation.

[0056] Other stabilizers (hereinafter referred to as "stabilizers") that can suppress the zirconium oxide phase transformation, besides yttrium oxide, include, for example, calcium oxide (CaO), magnesium oxide (MgO), cerium oxide (CeO2), scandium oxide (Sc2O3), niobium oxide (Nb2O5), lanthanum oxide (La2O3), erbium oxide (Er2O3), and praseodymium oxide (Pr2O3, Pr6O). 11 Oxides such as samarium oxide (Sm₂O₃), europium oxide (Eu₂O₃), thulium oxide (Tm₂O₃), gallium oxide (Ga₂O₃), indium oxide (In₂O₃), and ytterbium oxide (Yb₂O₃) are used. The aforementioned stabilizers can be used alone or in combination of two or more.

[0057] Furthermore, in the zirconia pre-calcined body of the present invention, from Y4Zr3O 12 From the viewpoint of achieving excellent light transmittance even at the highest sintering temperature for a shorter time (e.g., 2 minutes), it is preferable that the aforementioned zirconia includes monoclinic zirconia, and the monoclinic crystal ratio f calculated using formula (1-2) is... m (%) Less than 55%.

[0058] f m (%) = I m / (I m +I t +I c +I y +I d )×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; d This indicates the presence of Y4Zr3O 12 The area intensity of the peak near 2θ=29.6° at the summit of the main peak; I y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak where unsolidified yttrium oxide appears.

[0059] It should be noted that, due to Y4Zr3O 12 Since the main peaks of the tetragonal and cubic crystal systems are located close to each other, peak separation is used to calculate the area intensity of each main peak. From via Y4Zr3O 12 Based on the viewpoint that the monoclinic crystallinity f works in an integrated manner to achieve excellent light transmittance in the resulting zirconia sintered body even when held at the highest sintering temperature for 2 minutes, m (%) is more preferably 48% or less, further preferably 46% or less, and particularly preferably 45% or less.

[0060] 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.

[0061] As another suitable implementation method, from Y4Zr3O 12 From the perspective of achieving a unified structure while maintaining excellent light transmittance during a shorter holding time (e.g., 2 minutes) at the highest sintering temperature, examples include: [List of components containing Y4Zr3O] 12 As a crystal system, monoclinic indices f m (%) is 0% or more and less than 5% of the zirconia pre-fired body.

[0062] The zirconia pre-sintered body in the aforementioned embodiments only requires a monoclinic crystal ratio f m (%) is 0% or more and less than 5%, and there are no special restrictions. Examples include tetragonal zirconia and cubic zirconia.

[0063] 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).

[0064] 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.

[0065] In addition, the zirconia pre-calcined body of the present invention may be free of erbium oxide (Er2O3).

[0066] Examples of composite pigments mentioned above include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O 4· ZrSiO4, (Co,Zn)Al2O4, etc. 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] Furthermore, the content of the fluorescent agent is calculated based on the oxide of the metal element contained in the fluorescent agent. There are no limitations as long as suitable fluorescence is exhibited; it can be set to 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less. By setting this content to the lower limit or above, the fluorescence is comparable to that of natural human teeth. Furthermore, by setting this content to the upper limit or below, the reduction in light transmittance and mechanical strength can be suppressed.

[0072] Even when the zirconia pre-sintered body of the present invention is held at 1550°C for less than 7 minutes (e.g., 2 minutes), the resulting zirconia sintered body exhibits excellent light transmittance.

[0073] A sintered body prepared by calcining a zirconia pre-sintered body at 1550°C for 7 minutes at a heating rate of 350°C / min is designated as the first sintered body. A sintered body prepared by calcining a zirconia pre-sintered body of the same size as the zirconia pre-sintered body used to manufacture the first sintered body at 1550°C for 120 minutes at a heating rate of 10°C / min is designated as the second sintered body.

[0074] As a suitable embodiment of the present invention, the following zirconia pre-fired body, comprising zirconia and yttrium oxide, can be cited. When comparing the first translucency of a first sintered body prepared by calcining the aforementioned zirconia pre-sintered body at 1550°C for 7 minutes at a heating rate of 350°C / min with the second translucency of a second sintered body prepared by calcining the aforementioned zirconia pre-sintered body at 1550°C for 120 minutes at a heating rate of 10°C / min, The aforementioned first light transmittance is more than 85% of the aforementioned second light transmittance.

[0075] When the calcination time at 1550°C during the preparation of the first sintered body is set to 7 minutes, and the light transmittance of the first sintered body and the second sintered body are compared, the light transmittance of the first sintered body is preferably 85% or more of the light transmittance of the second sintered body, more preferably 90% or more, even more preferably 95% or more, and particularly preferably substantially equivalent.

[0076] As described above, the zirconia pre-calcined body of the present invention has advantages related to the short calcination time of less than 7 minutes.

[0077] Details of the aforementioned method for measuring light transmittance are described later in the examples.

[0078] Furthermore, as another suitable embodiment of the zirconia pre-fired body described in this invention, the following pre-fired body can be listed: it comprises zirconia, yttrium oxide, and Y4Zr3O. 12 The light transmittance of the first sintered body is within the aforementioned suitable range (e.g., more than 85%) relative to the light transmittance of the second sintered body.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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 3The following applies. When the density is within the aforementioned range, molding can be easily performed.

[0083] 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.

[0084] [Manufacturing method of zirconia pre-sintered body] Next, the manufacturing method of the zirconia pre-fired body will be explained.

[0085] 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.

[0086] As a method for manufacturing the zirconia pre-fired body of the present invention, the following manufacturing methods can be listed, which include: A process for manufacturing a zirconium oxide composition comprising zirconium oxide particles and yttrium oxide particles; A pulverizing 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 pulverizing process includes the pulverizing treatment specified below.

[0087] The method for manufacturing the zirconium oxide composition involves mixing zirconium oxide powder, which is used as a raw material powder, with yttrium oxide powder. The mixing method is not particularly limited, and known methods and apparatus can be used.

[0088] Methods for preparing zirconium oxide particles constituting zirconium oxide powder and yttrium oxide particles constituting yttrium oxide powder can employ, for example, a crushing process that achieves micronization by pulverizing or disintegrating coarse particles; or an aggregation process that synthesizes atoms or ions through a nucleation and growth process.

[0089] The zirconium oxide used to form the aforementioned zirconium oxide powder is not particularly limited; tetragonal, monoclinic, and cubic zirconium oxides may all be used.

[0090] In zirconium oxide powder, one type can be used alone, or two or more types can be used in combination.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Next, the zirconium oxide composition is further pulverized. During the pulverization process under specified conditions, by applying excessive energy compared to existing techniques, it is possible to obtain Y4Zr3O generated during pre-calcination. 12 Zirconia composition.

[0095] 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.

[0096] However, it can be inferred that in this invention, when a zirconium oxide composition containing zirconium oxide and yttrium oxide is subjected to a pulverization process, and the energy applied during this pulverization process is excessive compared to the prior art—in other words, when the pulverization process is performed with excessive energy applied compared to the past while simultaneously containing zirconium oxide and yttrium oxide—Y4Zr3O is generated during the manufacture of the pre-calcined body. 12 Therefore, even when the holding time at the highest sintering temperature is 2 minutes, it can still exhibit excellent light transmittance.

[0097] The following method is preferred for pulverizing.

[0098] (i) Use grinding media with a diameter of less than 1 mm, or (ii) Use grinding media with a diameter of more than 1 mm for a grinding time of more than 40 hours.

[0099] When using pulverizing media with a diameter less than 1 mm, Y4Zr3O is easily generated during the manufacture of the pre-calcined body by using pulverizing media with a fine diameter. 12 From this perspective, the preferred size is 0.1~0.5mm.

[0100] Commercially available products can be used as pulverizing media with a diameter of less than 1 mm.

[0101] Examples of grinding devices that use grinding media with a diameter of less than 1 mm include bead mills.

[0102] When using pulverizing media with a diameter of less than 1 mm, there is no particular limit to the pulverization time. Y4Zr3O is easily generated during the manufacture of the pre-calcined body. 12 From this perspective, a time of 10 minutes or more is preferred, more preferably 15 minutes or more, and even more preferably 20 minutes or more. Furthermore, the pulverization process is preferably 20 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and particularly preferably 2 hours or less.

[0103] 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).

[0104] 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.

[0105] Commercially available products can be used as pulverizing media with a diameter of 1 mm or more.

[0106] Examples of grinding devices that use grinding media with a diameter of 1 mm or more include ball mills.

[0107] When using pulverizing media with a diameter of 1 mm or more, the pulverizing time (pulverization treatment time) is not particularly limited, but preferably more than 40 hours, more preferably more than 55 hours, so that yttrium oxide particles can be easily pulverized to a very small size, and Y4Zr3O can be easily improved during the manufacture of pre-fired bodies. 12 Presence rate f d From this perspective, a further preferred time is 80 hours or more, particularly preferred is 100 hours or more. Furthermore, the pulverization process is preferably 1000 hours or less, more preferably 800 hours or less, further preferably 500 hours or less, and particularly preferably 300 hours or less.

[0108] In this invention, by supplying the zirconium oxide composition with a pulverizing energy that is adjusted and increased according to the combination of pulverizing time and pulverizing media diameter, it is possible to obtain Y4Zr3O generated during pre-calcination. 12 Zirconia composition.

[0109] It can be inferred that the zirconia composition obtained by applying excessive pulverizing energy through the above operation contains Y4Zr3O. 12 As a crystal system, it is easy to adjust to a more efficient and superior specified ratio.

[0110] Zirconia compositions can be in the form of particles, slurries, etc.

[0111] 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).

[0112] From the viewpoint that the light transmittance of the sintered body is excellent even when the holding time is 2 minutes at the highest sintering temperature, the average particle size of the zirconia composition after pulverization is preferably 0.2 μm or less.

[0113] 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.

[0114] 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.

[0115] Examples of adhesives include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic adhesives, wax adhesives, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.

[0116] 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.

[0117] Examples of plasticizers include polyethylene glycol, glycerin, propylene glycol, and dibutylphthalic acid.

[0118] 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.

[0119] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitol derivatives.

[0120] Examples of defoaming agents include alcohols, polyethers, polyethylene glycols, silicones, and waxes.

[0121] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxide such as tetramethylammonium hydroxide).

[0122] Examples of lubricants include polyoxyethylene alkyl ethers and waxes.

[0123] Examples of light transmittance modifiers include aluminum oxide (Al2O3), titanium dioxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0124] 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.), the formation of white turbidity in the sintered body can be suppressed 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.

[0125] 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).

[0126] 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.

[0127] 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.

[0128] There are no particular limitations on the molding method; for example, the following methods can be used.

[0129] (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) Processes such as stacking particles containing zirconium oxide particles and yttrium oxide particles.

[0130] (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.

[0131] 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.

[0132] 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.

[0133] (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.

[0134] 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.

[0135] Gelation can be achieved, for example, by adding a gelling agent, or by polymerizing a polymerizable monomer after its addition.

[0136] 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.

[0137] Furthermore, there are no particular limitations on the types of polymerizable monomers, but 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, etc.; N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N,N-bis(2-hydroxyethyl)(meth)acrylamide, etc. A single polymerizable monomer can be used, or two or more monomers can be used in combination.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] (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.

[0144] Specific methods of pressure molding include, for example, uniaxial pressure molding.

[0145] 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.

[0146] 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).

[0147] 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.

[0148] 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.

[0149] The aforementioned molded articles also include those that have been densified by high-temperature pressure treatment, such as CIP (Cold Isostatic Pressing).

[0150] Based on the same viewpoint as mentioned above, the CIP pressure is preferably 30~200MPa.

[0151] (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.

[0152] 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.

[0153] There is no particular limitation on the type of resin mentioned above, but the aforementioned adhesive is preferred.

[0154] (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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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).

[0169] The pressure applied during CIP processing is the same as described above for the instructions on pressure molding.

[0170] (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 produce granules by drying them in a spray dryer after slurry preparation, and the resulting granules can be used for powder lamination shaping.

[0171] There are no particular limitations on the powder lamination method, and examples include powder layering, SLS (Selective Laser Sintering), SLM (Selective Laser Melting), electron beam lamination, arc discharge lamination, and binder spraying. Regarding a better method that does not contain organic matter during lamination, it is preferable that organic matter is also not used in the particle manufacturing stage.

[0172] Next, the zirconia pre-fired body of the present invention is obtained by pre-firing the molded body.

[0173] Y4Zr3O is obtained by using the specific zirconium oxide composition described above, with the pre-firing temperature (maximum pre-firing temperature) as the pre-firing temperature in the pre-firing process. 12 Based on the viewpoint of ensuring a reliable semi-sintered state, the temperature 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.

[0174] Additionally, from the availability of Y4Zr3O 12 From the perspective of ensuring processability, the preheating temperature is preferably below 1300°C, more preferably below 1250°C, even more preferably below 1200°C, and particularly preferably below 1150°C.

[0175] That is, the preferred temperature for manufacturing the zirconia pre-fired body of the present invention is 600~1300°C.

[0176] Regarding the holding time (retention time) at the aforementioned highest pre-sintering temperature, as long as a semi-sintered state can be achieved and Y4Zr3O can be obtained, it is acceptable. 12 There are no particular limitations on the zirconia pre-fired body, but it is preferred to keep it at the highest pre-fired temperature for 30 minutes to 6 hours.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] [Zirconium oxide sintered body] Next, the sintered zirconia body will be described.

[0181] Zirconia sintered body is obtained by calcining the zirconia pre-sintered body obtained by the operation as described above.

[0182] The content of stabilizers (yttrium oxide and stabilizers other than yttrium oxide) in the zirconia sintered body of the present invention is the same as the content of stabilizers in the zirconia pre-sintered body.

[0183] When comparing the first light transmittance of a zirconia sintered body prepared by calcining the zirconia sintered body of the present invention at 1550°C for 7 minutes at a heating rate of 350°C / min with the second light transmittance of a zirconia sintered body prepared by calcining the zirconia sintered body at 1550°C for 120 minutes at a heating rate of 10°C / min, the aforementioned first light transmittance is preferably 85% or more of the aforementioned second light transmittance, more preferably 86% or more, further preferably 90% or more, particularly preferably 95% or more, and most preferably substantially equivalent.

[0184] Therefore, the zirconia sintered body of the present invention can maintain the same level of high light transmittance as that of long-term sintering after short-time sintering at 1550°C for a holding time of less than 7 minutes.

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

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

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

[0188] The content of colorant in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of colorant and the intended use of the zirconia sintered body. From the viewpoint of preferably using it as a dental patch, the content is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, based on the conversion of oxides of metal elements contained in the colorant, relative to 100% by mass of zirconia contained in the zirconia sintered body. In addition, the content of colorant, based on the conversion of oxides of metal elements contained in the colorant, is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, can be 0.1% by mass or less, and further can be 0.05% by mass or less.

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

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

[0191] The relative density of the zirconia sintered body is preferably 99.0% or more, more preferably 99.2% or more, and even more preferably 99.5% or more.

[0192] Relative density can be calculated as the ratio of the measured density, obtained by Archimedes' method, to the theoretical density.

[0193] The higher the density of the zirconia sintered body, the fewer the internal voids, and the less light scattering it is. Therefore, from the viewpoint of improving light transmittance, a density of 5.80 g / cm³ is preferred. 3 The above, more preferably 5.82 g / cm³ 3 The above is further optimized to 5.87 g / cm³. 3 The above. Zirconia sintered bodies are particularly preferred to be substantially free of voids.

[0194] Higher mechanical strength is preferred for zirconia sintered bodies. For example, the biaxial bending strength is preferably 800 MPa or higher, more preferably 820 MPa or higher, and even more preferably 840 MPa or higher. The biaxial bending strength can be measured according to ISO 6872:2015.

[0195] [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.

[0196] The preferred manufacturing method includes a step of calcining the aforementioned zirconia pre-sintered body at atmospheric pressure, above 1200°C and below 1700°C (hereinafter also referred to as the "calcination step"). This manufacturing method allows for the easy production of the zirconia sintered body of the present invention, which exhibits excellent light transmittance after a short sintering time of 2 minutes at the highest sintering temperature.

[0197] Furthermore, the manufacturing method of the present invention enables the easy manufacture of zirconia sintered bodies of the present invention that maintain the same level of high light transmittance as those produced by long-term calcination after short-time sintering at 1550°C for a holding time of less than 7 minutes.

[0198] When the zirconia pre-sintered body of the present invention is calcined to produce a sintered body, the highest sintering temperature is preferably the condition that the light transmittance of the zirconia sintered body reaches its maximum.

[0199] From the viewpoint that the desired zirconia sintered body can be easily 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 1700°C, more preferably below 1650°C, and even more preferably below 1600°C.

[0200] 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.

[0201] If the maximum sintering temperature is within the aforementioned range and is higher than the pre-firing temperature (maximum pre-firing temperature) in the pre-firing process, there is no particular limitation. For example, it can be set to any temperature that is 50°C or higher than the maximum pre-firing temperature, 100°C or higher than the maximum pre-firing temperature, 200°C or higher than the maximum pre-firing temperature, or 300°C or higher than the maximum pre-firing temperature.

[0202] When manufacturing sintered bodies, if the holding time at the highest sintering temperature is 7 minutes or less, the sintering time is not particularly limited. From the perspective of being able to obtain zirconia sintered bodies and the like with good productivity efficiently and stably, the holding time at the highest sintering temperature is preferably 5 minutes or less, more preferably 4 minutes or less, further preferably 3 minutes or less, and particularly preferably 2 minutes or less.

[0203] The holding time is preferably 30 seconds or more, more preferably 45 seconds or more, and even more preferably 1 minute or more.

[0204] By using the zirconia pre-sintered body of the present invention, the light transmittance of the zirconia sintered body is not reduced during its manufacture, 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 7 minutes or less (e.g., 2 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 treatment using the dental article can be shortened, and the time burden on patients can be reduced. Furthermore, energy costs can be reduced. Moreover, by keeping the holding time at the highest sintering temperature below the aforementioned upper limit, the deactivation of fluorescent agents can be suppressed.

[0205] 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.

[0206] 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.

[0207] Commercially available dental calcining furnaces (such as the trade name "Sintra CS" (manufactured by Shenpaz)) can be used.

[0208] 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.

[0209] 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".

[0210] HIP processing can be performed using a known hot isostatic pressing (HIP) apparatus.

[0211] 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.

[0212] 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.

[0213] 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.

[0214] 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.).

[0215] 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%.

[0216] 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.

[0217] 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.

[0218] An atmosphere with excess oxygen refers to an atmosphere where the oxygen concentration is higher than that in the atmosphere.

[0219] 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%.

[0220] 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.

[0221] 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.

[0222] 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.

[0223] In another suitable embodiment, from the viewpoint of the aesthetics of the zirconia sintered body, the heat treatment temperature in the atmosphere or in an oxygen-excess atmosphere is preferably below 1400°C, more preferably below 1300°C, and even more preferably below 1200°C.

[0224] 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.

[0225] 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.).

[0226] The zirconia sintered body obtained by calcining the zirconia pre-burnt body of the present invention is suitable for use in dental products.

[0227] 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.

[0228] By using the zirconia pre-fired body of the present invention in components such as implant screws and implant fixation devices, it is possible to suppress gingival discoloration and achieve excellent aesthetics when using metal materials.

[0229] 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.

[0230] 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.

[0231] As a suitable embodiment (X-1), a zirconia sintered body is provided, which includes zirconia and a stabilizer capable of suppressing the zirconia phase transformation. At least one zirconia crystal grain in the zirconia sintered body has a portion having a concentration gradient of the stabilizer in the same crystal grain that gradually decreases from the center side of the grain toward the grain boundary on the outside.

[0232] As the zirconia sintered body described in this embodiment (X-1), it is sufficient that at least one zirconia crystal particle has a portion having the aforementioned concentration gradient. Depending on the unevenness of the content of the aforementioned stabilizer (concentration unevenness), it may include a portion in which the tendency of the content of the aforementioned stabilizer to increase or decrease changes.

[0233] The stabilizer in the zirconia sintered body described in this embodiment (X-1) can be the same substance as yttrium oxide and other stabilizers that can suppress the zirconia phase transformation that can be used in the zirconia pre-sintered body described in this invention.

[0234] From the viewpoint of superior light transmittance, the zirconia sintered body described in this embodiment (X-1) is preferably yttrium oxide, which is capable of suppressing the zirconia phase transformation.

[0235] As the zirconia sintered body described in this embodiment (X-1), it is preferred to be a zirconia sintered body with a concentration gradient of 0.1 to 3 mol% relative to the total molarity of zirconia and stabilizer.

[0236] From the viewpoint of excellent light transmittance, the aforementioned concentration gradient (the difference in content between the center side and the grain boundary) is preferably 0.15 mol% or more, more preferably 0.2 mol% or more, even more preferably 0.3 mol% or more, and particularly preferably 0.5 mol% or more. Furthermore, from the viewpoint of excellent light transmittance, the aforementioned concentration gradient is preferably 2.8 mol% or less, more preferably 2.5 mol% or less, even more preferably 2.2 mol% or less, and particularly preferably 2.0 mol% or less.

[0237] The evaluation method for the aforementioned concentration gradient is as described in the examples described later.

[0238] Hereinafter, with regard to the zirconia sintered body described in this embodiment (X-1), as a suitable example, a zirconia sintered body in which yttrium oxide is used as the stabilizer to suppress the zirconia phase transformation will be described.

[0239] Regarding the zirconia sintered body described in this embodiment (X-1), in the case of Y4Zr3O 12 When calcined as a crystalline zirconia pre-sintered body, it exhibits excellent light transmittance even when held at the highest sintering temperature for 2 minutes.

[0240] When zirconia sintered bodies possessing the aforementioned properties are observed using a transmission electron microscope (TEM), such as... Figure 2 As shown, the portion having a yttrium oxide content that gradually decreases in the direction indicated by the arrow, i.e., from the center side (e.g., the center portion 1) toward the grain boundary.

[0241] The aforementioned central side, located inside the same crystalline grain, can be any central part, such as the centroid (geometric center). The centroid can be determined using well-known analysis software (e.g., image analysis software, such as "Image-Pro Plus," manufactured by Berton). The centroid can be determined based on the outline of the crystalline grain.

[0242] As is known in the prior art, during the final stage of sintering, when observed using a transmission electron microscope (TEM), there is a concentration gradient in the yttrium oxide concentration within the same crystalline grain, which gradually decreases from the outer grain boundaries towards the center. Therefore, the zirconia sintered body described in this embodiment (X-1) exhibits a tendency completely opposite to that of the prior art.

[0243] Regarding the manufacturing method of the zirconia sintered body described in this embodiment (X-1), the manufacturing method is not particularly limited as long as the zirconia sintered body has the aforementioned crystalline grain structure. The zirconia sintered body described in this embodiment (X-1) is suitable for obtaining a Y4Zr3O-containing zirconia sintered body by performing a pulverization process with an excessive amount of energy applied compared to conventional methods while simultaneously containing zirconia and yttrium oxide. 12 As a crystalline zirconia pre-burnt body, it can be manufactured by calcining the aforementioned zirconia pre-burnt body, thereby utilizing a short calcination time (e.g., a holding time of 2 minutes at the highest sintering temperature).

[0244] Alternatively, it can be considered that in the zirconia sintered body described in this embodiment (X-1), by performing short-time calcination (e.g., holding time of 2 minutes at the highest sintering temperature), at least one of the zirconia crystal particles has a yttrium oxide concentration gradient.

[0245] Furthermore, it can be considered that in the zirconia sintered body described in this embodiment (X-1), by having a yttrium oxide concentration gradient, in cubic crystals that are generally said to have high light transmittance but low mechanical strength, by having a low yttrium oxide region with a toughening mechanism (stress-induced phase transformation) at the edge (grain boundary) of the zirconia crystal particles, even if a zirconia sintered body is produced in a short calcination time (e.g., a holding time of 2 minutes at the highest sintering temperature), it is possible to take into account both excellent mechanical strength and light transmittance.

[0246] The yttrium oxide content of the aforementioned zirconia crystal particles can be determined using, for example, scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS).

[0247] As a more suitable embodiment (X-1-1), the following zirconia sintered body can be listed, which contains zirconia and yttrium oxide as components and contains Y4Zr3O 12 The zirconia sintered body, obtained by calcining a zirconia pre-sintered body, contains zirconia and a stabilizer capable of suppressing the zirconia phase transformation. At least one zirconia crystal grain in the zirconia sintered body has a portion having a concentration gradient of the stabilizer in the same crystal grain that gradually decreases from the center of the grain toward the grain boundary.

[0248] Alternatively, as another suitable embodiment (X-2), the following zirconia sintered body can be listed, which includes zirconia and a stabilizer capable of inhibiting the zirconia phase transformation, wherein the aforementioned zirconia sintered body comprises: The aforementioned stabilizer content is 4-6 mol% (L) of zirconia crystalline particles relative to the total molar percentage of zirconia and stabilizer; and The aforementioned stabilizer content is 1~3 mol% of the total molar content of zirconium oxide and stabilizer in zirconium oxide crystal particles (S).

[0249] In TEM observation, the number of zirconia crystal particles (L) observed within a 5 μm × 5 μm range is preferably 3 or more, more preferably 5 or more, further preferably 7 or more, and particularly preferably 10 or more. In TEM observation, the number of zirconia crystal particles (S) observed within a 5 μm × 5 μm range is preferably 5 or more, more preferably 10 or more, further preferably 15 or more, and particularly preferably 20 or more.

[0250] The zirconia sintered body described in this embodiment (X-2) is not particularly limited and may contain zirconia crystalline particles in which the content of the aforementioned stabilizer is more than 3 mol% and less than 4 mol% relative to the total molarity of zirconia and stabilizer.

[0251] The stabilizer in the zirconia sintered body described in this embodiment (X-2) can be the same substance as yttrium oxide and other stabilizers that can suppress the zirconia phase transformation that can be used in the zirconia pre-sintered body described in this invention.

[0252] From the viewpoint of superior light transmittance, the zirconia sintered body described in this embodiment (X-2) is preferably yttrium oxide, which is capable of suppressing the zirconia phase transformation.

[0253] From the viewpoint of superior light transmittance and mechanical strength, the zirconia sintered body described in this embodiment (X-2) is preferably a zirconia sintered body with an average grain diameter of 0.5 to 2.0 μm for the aforementioned zirconia crystal particles (L) and an average grain diameter of 0.1 to 0.3 μm for the aforementioned zirconia crystal particles (S).

[0254] In the zirconia sintered body described in this embodiment (X-2), from the viewpoint of superior light transmittance and mechanical strength, the average grain diameter of the aforementioned zirconia crystal particles (L) is preferably 0.5 μm or more, more preferably 0.6 μm or more, even more preferably 0.7 μm or more, and particularly preferably 0.8 μm or more.

[0255] Furthermore, from the viewpoint of superior light transmittance and mechanical strength, the average grain diameter of the aforementioned zirconia crystal particles (L) is preferably 2.0 μm or less, more preferably 1.5 μm or less, even more preferably 1.3 μm or less, and particularly preferably 1.2 μm or less.

[0256] In the zirconia sintered body described in this embodiment (X-2), from the viewpoint of superior light transmittance and mechanical strength, the average grain diameter of the aforementioned zirconia crystal particles (S) is preferably 0.10 μm or more, more preferably 0.12 μm or more, even more preferably 0.15 μm or more, and particularly preferably 0.18 μm or more.

[0257] Furthermore, from the viewpoint of superior light transmittance and mechanical strength, the average grain diameter of the aforementioned zirconia crystal particles (S) is preferably 0.3 μm or less, more preferably 0.28 μm or less, even more preferably 0.25 μm or less, and particularly preferably 0.22 μm or less.

[0258] The method for determining the average grain diameter of the aforementioned zirconia crystal particles (L) and zirconia crystal particles (S) is as described in the examples described later.

[0259] Hereinafter, with regard to the zirconia sintered body described in this embodiment (X-2), as a suitable example, a zirconia sintered body in which yttrium oxide is used as the stabilizer to suppress the zirconia phase transformation will be described.

[0260] Regarding the manufacturing method of the zirconia sintered body described in this embodiment (X-2), the manufacturing method is not particularly limited as long as the zirconia sintered body has the aforementioned crystalline grain structure. The zirconia sintered body described in this embodiment (X-2) is suitable for obtaining a Y4Zr3O-containing zirconia sintered body by performing a pulverization process with an excessive amount of energy compared to conventional methods while simultaneously containing zirconia and yttrium oxide. 12 As a crystalline zirconia pre-burnt body, it can be manufactured by calcining the aforementioned zirconia pre-burnt body, thereby utilizing a short calcination time (e.g., a holding time of 2 minutes at the highest sintering temperature).

[0261] Alternatively, it can be considered that in the zirconia sintered body described in this embodiment (X-2), a zirconia sintered body containing the aforementioned zirconia crystal particles (L) and zirconia crystal particles (S) is formed by performing short-time calcination (e.g., holding time at the highest sintering temperature is 2 minutes).

[0262] Furthermore, it can be considered that in the zirconia sintered body described in this embodiment (X-2), by including zirconia crystal particles (L) and zirconia crystal particles (S) exhibiting the aforementioned stabilizer content (suitably yttrium oxide content) and average grain diameter, it is possible to utilize fine crystal particles to ensure mechanical strength and reduce light interference in the visible light region. Even when a zirconia sintered body is produced under short-time calcination (e.g., a holding time of 2 minutes at the highest sintering temperature), it is possible to achieve both excellent mechanical strength and light transmittance.

[0263] Regarding the zirconia sintered body described in this embodiment (X-2), for the zirconium oxide containing Y4Zr3O 12 When calcined as a crystalline zirconia pre-sintered body, it exhibits excellent light transmittance even when held at the highest sintering temperature for 2 minutes.

[0264] It can be considered that in the zirconia sintered body described in this embodiment (X-2), by including a region with a high yttrium oxide content of 4 to 6 mol% zirconia crystal particles (L) and a region with a low yttrium oxide content of 1 to 3 mol% zirconia crystal particles (S), a crystalline structure combining high-strength tetragonal crystals and high-transparency cubic crystals is formed, thus achieving both excellent strength and light transmittance as a sintered body.

[0265] As a more suitable embodiment (X-2-1), the following zirconia sintered body can be listed, which contains zirconia and yttrium oxide as components and contains Y4Zr3O 12 The sintered zirconia body, obtained by calcining a pre-calcined zirconia body with a crystalline structure, comprises zirconia and a stabilizer capable of inhibiting the zirconia phase transformation. The aforementioned zirconia sintered body includes: The concentration of the aforementioned stabilizer relative to the total molar concentration of zirconium oxide and stabilizer is 4-6 mol% of zirconium oxide crystalline particles (L); and The concentration of the aforementioned stabilizer relative to the total molar concentration of zirconium oxide and stabilizer is 1-3 mol% of zirconium oxide crystal particles (S).

[0266] From the viewpoint of superior light transmittance and mechanical strength, the zirconia sintered body described in this embodiment (X-2) is more preferably the following zirconia sintered body, which comprises: The concentration of the aforementioned stabilizer relative to the total molar concentration of zirconium oxide and stabilizer is 5-6 mol% of zirconium oxide crystalline particles (Lx); and The concentration of the aforementioned stabilizer relative to the total molar concentration of zirconium oxide and stabilizer is 1-2 mol% of zirconium oxide crystal particles (Sx).

[0267] Furthermore, from the viewpoint of superior light transmittance and mechanical strength, it is even more preferable that the average grain diameter of the zirconia crystal particles (Lx) is within the range of the average grain diameter of the zirconia crystal particles (L), and the average grain diameter of the zirconia crystal particles (Sx) is within the range of the average grain diameter of the zirconia crystal particles (S).

[0268] Furthermore, as another suitable embodiment (X-3), the following zirconia sintered body can be listed, which includes zirconia and a stabilizer capable of suppressing the zirconia phase transformation, wherein at least one zirconia crystal grain in the aforementioned zirconia sintered body has a portion having a concentration gradient of the aforementioned stabilizer in the same crystal grain that gradually decreases from the center side of the grain towards the grain boundary. The aforementioned zirconia crystal particles are zirconia crystal particles (L) with a stabilizer content of 4~6 mol% relative to the total molar content of zirconia and stabilizer. The zirconia sintered body further comprises zirconia crystalline particles (S) with a content of the aforementioned stabilizer relative to the total molar percentage of zirconia and stabilizer of 1 to 3 mol%.

[0269] Regarding the concentration gradient of the aforementioned zirconia crystal particles in the zirconia sintered body described in this embodiment (X-3), as explained in the above embodiment (X-1).

[0270] Furthermore, regarding the zirconia crystal particles (L) and zirconia crystal particles (S) in the zirconia sintered body described in this embodiment (X-3), as explained in the above embodiment (X-2).

[0271] In this embodiment (X-3), from the viewpoint of superior light transmittance and mechanical strength, the zirconia crystal particles having the aforementioned concentration gradient are zirconia crystal particles (L).

[0272] As the zirconia sintered body described in this embodiment (X-3), when arbitrarily selecting 10 zirconia crystal particles (L) in a TEM image (1 field of view) obtained by TEM observation of the zirconia sintered body, it is preferable that there are 5 or more zirconia crystal particles (L) having the aforementioned concentration gradient among the 10 particles, more preferably 6 or more, and even more preferably 7 or more.

[0273] It should be noted that if less than 10 zirconia crystal particles (L) can be obtained from one field of view, the number of fields of view can be increased to select a total of 10 zirconia crystal particles (L).

[0274] In this manual, when selecting a specific number of crystal particles (e.g., 10 or 20) in one field of view, if the target number of particles cannot be identified in one field of view, the number of fields of view can be increased to two or more, and the total number of target particles selected can be (e.g., 10 or 20).

[0275] As a more suitable embodiment (X-3-1), the following zirconia sintered body can be listed, which contains zirconia and yttrium oxide as components and contains Y4Zr3O 12 The sintered zirconia body, obtained by calcining a zirconia pre-sintered body, comprises zirconia and yttrium oxide. At least one zirconia crystal grain in the sintered zirconia body has a portion having a concentration gradient of yttrium oxide within the same crystal grain, where the concentration (content) gradually decreases from the center of the grain towards the grain boundary. The aforementioned zirconia crystal particles are zirconia crystal particles (L) with a yttrium content of 4-6 mol% relative to the total molar content of zirconia and yttrium. The zirconia sintered body further comprises zirconia crystalline particles (S) with a yttrium content of 1 to 3 mol% relative to the total molar content of zirconia and yttrium.

[0276] As another suitable embodiment (X-3-2), a more preferred embodiment is the following zirconia sintered body, comprising: The concentration of the aforementioned stabilizer relative to the total molar concentration of zirconium oxide and stabilizer is 5-6 mol% of zirconium oxide crystalline particles (Lx); and The concentration of the aforementioned stabilizer relative to the total molar concentration of zirconium oxide and stabilizer is 1-2 mol% of zirconium oxide crystal particles (Sx). Zirconia crystal particles having a concentration gradient of the aforementioned stabilizer are zirconia crystal particles (Lx).

[0277] Furthermore, as another suitable embodiment (X-3-3), from the viewpoint of superior light transmittance and mechanical strength, it is further preferred that the average grain diameter of the zirconia crystal particles (Lx) is within the range of the average grain diameter of the zirconia crystal particles (L), and the average grain diameter of the zirconia crystal particles (Sx) is within the range of the average grain diameter of the zirconia crystal particles (S).

[0278] Furthermore, the zirconia sintered body described in this embodiment (X-3) is not particularly limited, and may contain zirconia crystalline particles in which the content of the aforementioned stabilizer is more than 3 mol% and less than 4 mol% relative to the total molarity of zirconia and stabilizer.

[0279] 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.

[0280] For example, in suitable implementations (X-1) to (X-3), all or part of the configuration can be combined in various ways within the scope described in this specification.

[0281] Specifically, embodiments in which the biaxial bending strength of the zirconia sintered body described in suitable embodiments (X-1) to (X-3) is 800 MPa or higher are also included in this invention. Example

[0282] 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.

[0283] [Example 1] Commercially available zirconium oxide powder (Y2O3: 0 mol%) and commercially available yttrium oxide powder were added to water. They and zirconium oxide grinding media (diameter: 2 mm) were then added to the container of a ball mill. The grinding process was set to 144 hours, and the ball mill was used to grind the materials to obtain a slurry (average particle size: below 0.2 μm).

[0284] 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.

[0285] The powder is fed into a cylindrical mold and pressed under uniaxial pressure of 200 MPa to obtain a molded body.

[0286] 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 955°C (the maximum pre-firing temperature) for 2 hours. Finally, it was slowly cooled at a rate of -10°C / min to obtain a zirconia pre-fired body.

[0287] [Examples 2-11 and Comparative Examples 1-4] Except for the conditions described in Table 1, zirconia pre-fired bodies were manufactured using the same method as in Example 1. In Examples 2-11 and Comparative Examples 1-4, the yttrium oxide raw material used was the same as that in Example 1.

[0288] It should be noted that in Example 4, the pulverization process is replaced by the pulverization process in the ball mill. Instead, a pulverizing media with a diameter of 0.1 mm is used and the pulverization process is carried out using a ball mill. The pulverization time is changed to that recorded in Table 1.

[0289] In Example 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, with the pulverization time of each process changed to the pulverization time recorded in Table 1.

[0290] It should be noted that, in Table 1, 1.5Y zirconium oxide (Y2O3: 1.5 mol%) is manufactured as follows.

[0291] 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.

[0292] In Table 1, 40Y zirconium oxide (Y2O3: 40 mol%) is manufactured as follows.

[0293] 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.

[0294] [Table 1] .

[0295] Does Y4Zr3O exist in the zirconia pre-sintered body? 12 Evaluation > The presence of Y4Zr3O in the zirconia pre-sintered bodies obtained in each embodiment and comparative example. 12 Evaluation was conducted using TEM.

[0296] Specifically, the pre-burnt body was ground until a thickness of 30 μm was achieved, and the surface of the pre-burnt body was processed using a precision ion polishing system (trade name "Model 691 PIPS", manufactured by Gatan Corporation (US)). Using the prepared sample, electron X-ray diffraction images were acquired using an atomic resolution analytical electron microscope (trade name "JEM-ARM200F ACCELARM", manufactured by Nippon Electron Ltd.) at a camera length of 1.0 cm and an accelerating voltage of 200 kV.

[0297] First, based on the obtained diffraction pattern, such as Figure 1 The distances d1 and d2 (equivalent to the interplane spacing) and their angles (equivalent to the interplane angle φ) of the diffraction points are measured as shown.

[0298] Next, using the substitution of Y4Zr3O 12 The lattice constants (a = 9.738 Å, c = 9.115 Å) of the hexagonal crystal are calculated using equations (1-3) and (1-4) to determine whether there exists a combination of facet indices (h1, k1, l1) and (h2, k2, l2) corresponding to the measured facet spacing (d1, d2) and facet angle (φ). It should be noted that regarding Y4Zr3O 12 The lattice constant is referenced in "Magnetic Susceptibility of M4Zr3O". 12 AND M4Hf3O 12(M-RARE-EARTH ELEMENT)" Inorg.Mater., 1991, 27, pp.1495-1497, Red'ko VP, Lopato LM".

[0299] 1 / d 2 =4 / 3 ((h) 2 +hk+k 2 ) / a 2 )+l 2 / c 2 (1-3) cosφ=(h1h2+k1k2+1 / 2(h1k2+h2k1)+(3a 2 / 4c 2 )l1l2) / ((h1) 2 +k1 2 +h1k1+(3a 2 / 4c 2 )l1 2 (h2) 2 +k2 2 +h2k2+(3a 2 / 4c 2 l2 2 )) 1 / 2 (1-4) When evaluated according to the above method, it can be confirmed that Y4Zr3O is present in the zirconia pre-fired bodies of Examples 1-11. 12 On the other hand, Y4Zr3O was not found in the zirconia pre-sintered bodies of Comparative Examples 1-4. 12 The existence of.

[0300] Evaluation of the Prevalence of Crystal Systems in Zirconia Pre-sintered Materials Y4Zr3O of the zirconia pre-sintered bodies obtained in the various embodiments and comparative examples 12 Presence rate f d , 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.

[0301] 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.

[0302] 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° Using the area intensity of each peak, calculate Y4Zr3O according to equations (1-1) and (1-2) above. 12 Presence rate f d (%) and monoclinic crystallinity f m (%). The results are shown in Table 2.

[0303] It should be noted that in Y4Zr3O 12 Presence rate f d In the calculation of (%), due to Y4Zr3O 12 Since the main peak positions of the tetragonal and cubic crystal systems are close, peak separation is performed when the coexistence of these crystal systems is confirmed. Specifically, the existence of each crystal system is first confirmed.

[0304] Regarding Y4Zr3O 12 The presence of TEM is confirmed through evaluation.

[0305] Regarding the tetragonal crystal system, its existence is confirmed by the secondary peaks near 34.6° and 35.4°.

[0306] Regarding the cubic crystal system, its existence is confirmed by the secondary peak near 35.0°.

[0307] Next, peak separation is performed based on the identified crystal system. For example, in the case where all three crystal systems are identified, the peaks of the three crystal systems that overlap around 30° are separated to form the peak of Y4Zr3O with a peak at 29.6°. 12 The peaks of the three crystal systems—a tetragonal crystal with a peak at 30.3°, a cubic crystal with a peak at 30.0°—are approximated by Gaussian functions. By adjusting the half-width and peak intensity at the aforementioned peak positions, separation is achieved, and the area intensity I of each system is calculated. d I t I c If two crystal systems are confirmed to exist, the peaks of the two crystal systems are separated, and their respective area intensities are calculated.

[0308] Evaluation of the crystalline grains of zirconia sintered bodies After determining the zirconia crystal particles in the zirconia sintered body according to the following steps, the yttrium oxide content of the zirconia crystal particles, the average grain diameter of the zirconia crystal particles (L) and (S), and the concentration gradient of yttrium oxide in the zirconia crystal particles are measured.

[0309] <Method for identifying zirconia crystal particles> The following method is used to identify zirconia crystal particles (zirconia concentration of 80% by mass or more).

[0310] When measuring in the bright field (20,000x) of TEM observation, the scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS) method is used, including observation points with a zirconium oxide concentration of 80% by mass or more (observation range of 5×5nm). Particles with almost constant brightness in visual judgment are regarded as zirconium oxide crystal particles.

[0311] <Yttrium oxide content in zirconia crystal particles> In the zirconium oxide crystal particles identified as described above, the yttrium oxide content was determined using STEM-EDS. Here, the observation range was set to a square shape, with at least three vertices of the aforementioned square inscribed within the grain boundaries of the crystal particles, thus forming the largest possible square shape within the crystal particles.

[0312] In the zirconia sintered body of Example 1 obtained by calcination using the method described later in <Evaluation of the Transmittance of Zirconia Sintered Body (Determination of ΔL* (WB) 1)> (short-time calcination at 1580°C for 2 minutes), there were more than 100 zirconia crystal particles with a yttrium oxide content in the range of 4 to 6 mol% and more than 100 zirconia crystal particles with a yttrium oxide content in the range of 1 to 3 mol% (totaling 10 field-of-view quantities).

[0313] Furthermore, there were more than 100 zirconium crystal particles with a yttrium content of 5-6 mol% and more than 100 zirconium crystal particles with a yttrium content of 1-2 mol% (totaling 10 field-view quantities).

[0314] On the other hand, in the zirconia sintered body of Comparative Example 3, only zirconia crystal particles contained in the range of 4 to 6 mol% were present, and zirconia crystal particles contained in the range of 1 to 3 mol% were not identified.

[0315] <Method for determining the average grain diameter of zirconia crystal grains (L) and (S)> Next, zirconia crystal particles with a yttrium oxide content in the range of 4 to 6 mol% were designated as zirconia crystal particles (L), and zirconia crystal particles with a yttrium oxide content in the range of 1 to 3 mol% were designated as zirconia crystal particles (S). The equivalent diameter of each crystal particle (area circle equivalent diameter) determined by the aforementioned zirconia crystal particle discrimination method using TEM observation was designated as the grain diameter of each crystal particle. The arithmetic mean of the equivalent diameters of arbitrarily selected 100 crystal particles was designated as the average grain diameter of the zirconia crystal particles.

[0316] More specifically, for the quantities of 10 fields of view, the arithmetic mean of the circular equivalent diameter of 10 arbitrarily selected crystal grains in one field of view is calculated and set as the average grain diameter of the zirconia crystal grains.

[0317] In the zirconia sintered body of Example 1, the average grain diameter of the zirconia crystal particles (L) is 1.0 μm, and the average grain diameter of the zirconia crystal particles (S) is 0.2 μm.

[0318] Alternatively, zirconia crystal particles with a yttrium oxide content in the range of 5 to 6 mol% can be designated as zirconia crystal particles (Lx), and zirconia crystal particles with a yttrium oxide content in the range of 1 to 2 mol% can be designated as zirconia crystal particles (Sx). In this case, in the zirconia sintered body of Example 1, the average grain diameter of the zirconia crystal particles (Lx) is 1.2 μm, and the average grain diameter of the zirconia crystal particles (Sx) is 0.2 μm.

[0319] Determination of the concentration gradient of yttrium oxide in zirconia crystal particles In the zirconia crystal grains identified as described above using TEM observation, the yttrium oxide content at the central portion and grain boundaries was determined using STEM-EDS (observation range 5×5 nm). Here, the content at the central portion was measured at the centroid of the crystal grain, and the content at the grain boundaries was measured in a region representing 1 / 10 of the distance from the grain boundary to the centroid. In the zirconia sintered body of Example 1, when any zirconia crystal grain (L) was selected and measured, the yttrium oxide content in the zirconia crystal grains was 5.9 mol% at the central portion (centroid) and 4.2 mol% at the grain boundaries. Furthermore, when 10 arbitrary zirconia crystal grains (L) were selected from multiple fields of view and measured, it was confirmed that 9 zirconia crystal grains had a yttrium oxide content that was at least 0.15 mol% lower than that at the grain boundaries compared to the central portion (centroid).

[0320] On the other hand, in the zirconia sintered body of Comparative Example 3, the yttrium oxide content in the central part (center of gravity) and the grain boundaries of the zirconia crystal grains is the same or the yttrium oxide content at the grain boundaries is higher than that in the central part (center of gravity).

[0321] The center of gravity of the aforementioned crystalline particles was determined using image analysis software (trade name "Image-Pro Plus", manufactured by Berton Corporation) from the outline of the crystalline particles.

[0322] <Evaluation of the light transmittance of zirconia sintered bodies (determination of ΔL* (WB) 1)> For the zirconia pre-burnt bodies obtained in each embodiment and comparative example, a short-time calcination was carried out using a dental calcination furnace (trade name "Sintra CS" (manufactured by Shenpaz)) at a heating rate of 350°C / min and a holding time of 2 minutes at 1580°C.

[0323] The obtained zirconia sintered bodies were ground into flat plates with a thickness of 1.0 mm, which were used as test samples for transmittance. The transmittance of these samples was measured using an Olympus spectrophotometer (trade name "Crystaleye") in 7-band LED light source mode.

[0324] Similar to the determination of the light transmittance of zirconia sintered bodies (ΔL*(WB)) below, the lightness (LW*) when measuring chromaticity against a white background and the lightness (LB*) when measuring chromaticity against a black background using the same sample, the same measuring device, the same measuring mode and the same light source were measured. The difference between the two (ΔL*=(LW*)-(LB*)) was set as the light transmittance (ΔL*(WB)) (arithmetic mean of n=3).

[0325] As for light transmittance ΔL* (WB), a value of 13 or higher is considered acceptable. The results are shown in Table 2 below.

[0326] <Evaluation of the light transmittance of zirconia sintered bodies (ΔL* (WB)) 2> In addition, for the pre-sintered bodies obtained in the examples and comparative examples, the maximum sintering temperature was set to 1550°C, and the holding time at the maximum sintering temperature was set to 7 minutes (calcination for 7 minutes) at a heating rate of 350°C / min to produce a zirconia sintered body (first sintered body).

[0327] Next, for the pre-sintered body prepared using the same method, the maximum sintering temperature was set to 1550℃, and the holding time at the maximum sintering temperature was set to 120 minutes (calcination for 120 minutes) at a heating rate of 10℃ / min to produce a zirconia sintered body (second sintered body).

[0328] Regarding the cooling rate, it was set to 200℃ / min for 7 minutes of calcination and 10℃ / min for 120 minutes of calcination.

[0329] The two types of zirconia sintered bodies were ground into flat samples with a thickness of 1.0 mm, which were used as samples for transmittance testing. The transmittance of these samples was measured using an Olympus spectrophotometer (trade name "Crystaleye") in 7-band LED light source mode.

[0330] Specifically, regarding the transmittance of zirconia sintered bodies as flat samples, the lightness (LW*) measured against a white background and the lightness (LB*) measured against a black background using the same sample, measuring apparatus, measuring mode, and light source are taken as the transmittance (ΔL*(WB)) (arithmetic mean of n=3). The L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013).

[0331] Calculate the first translucency ΔL1*(WB) of the first sintered body prepared by calcination at 1550℃ for 7 minutes and the second translucency ΔL2*(WB) of the second sintered body prepared by calcination at 1550℃ for 120 minutes. Calculate the ratio of ΔL1*(WB) to ΔL2*(WB) (ΔL1*(WB) / ΔL2*(WB)) as the rate of change of translucency.

[0332] As the rate of change in light transmittance, a value of 0.85 or higher (85% or higher) is considered acceptable. The results are shown in Table 2 below.

[0333] <Strength Evaluation of Zirconia Sintered Bodies> In Example 1, the zirconia sintered body obtained by calcination using the method described in the aforementioned <Evaluation of the Transmittance of Zirconia Sintered Body (Determination of ΔL*(WB) 1)> (short-time calcination at 1580°C for 2 minutes) was directly tested using a 1.0 mm thick flat plate sample after grinding. The biaxial bending strength (n=5) was measured using a universal testing machine "AGS-X" (manufactured by Shimadzu Corporation) with the crosshead speed set to 1.0 mm / min, according to ISO 6872:2015. The calculated arithmetic mean was 911 MPa.

[0334] In contrast, the commercially available product of Comparative Example 3 was used, and the biaxial bending strength was measured and calculated in the same manner as in Example 1, and the result was 600 MPa.

[0335] [Table 2] .

[0336] Based on the above results, it can be confirmed that even when the holding time at the highest sintering temperature is 2 minutes, the light transmittance of the zirconia pre-sintered body of the present invention is excellent.

[0337] Furthermore, by using the zirconia pre-sintered body of the present invention, the maximum sintering temperature can be set to below 1600°C. For example, when the maximum sintering temperature is set to 1550°C, a zirconia sintered body that can maintain the same level of high light transmittance as long-term sintered bodies after short-time sintering at 1550°C with a holding time of less than 7 minutes can be obtained.

[0338] In the comparative example, when the holding time at the highest sintering temperature was 2 minutes, the sintering was not sufficiently carried out to achieve the target light transmittance.

[0339] Furthermore, it can be confirmed that the zirconia crystal particles of the zirconia sintered body with excellent light transmittance obtained by using a manufacturing method that holds the pre-burned body at the highest sintering temperature for 2 minutes have characteristics different from those observed in sintered bodies of the prior art.

[0340] Industrial utilization The zirconia pre-fired body of the present invention is useful for manufacturing dental articles used in dental hospital treatments.

Claims

1. A zirconia calcine comprising zirconia, yttria, and Y4Zr30i as a crystal system. 12 .

2. The zirconia calcine according to claim 1, wherein the presence ratio f (%) of Y4Zr3O12 calculated using the following formula (1-1) is 2.5% or greater. 12 f = (Y4Zr3O12) / (ZrO2) x 100 d (%). f d (%)=I d / (I m +I t +I c +I y +I d )×100 (1-1) In the formula, f d Y4Zr3O 12 Presence rate (%); 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; d This indicates the presence of Y4Zr3O 12 The area intensity of the peak near 2θ=29.6° at the summit of the main peak; I y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak where unsolidified yttrium oxide appears. Additionally, due to Y4Zr3O 12 Since the main peaks of the tetragonal and cubic crystal systems are located close to each other, the area intensity of each main peak can be calculated by peak separation.

3. The zirconia pre-fired body according to claim 1 or 2, wherein, The zirconium oxide comprises monoclinic zirconium oxide, and the monoclinic crystal ratio f is calculated using the following formula (1-2). m (%) less than 55%, f m (%)=I m / (I m +I t +I c +I y +I d )×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; d This indicates the presence of Y4Zr3O 12 The area intensity of the peak near 2θ=29.6° at the summit of the main peak; I y This represents the area intensity of the peak near 2θ=29.2° at the apex of the main peak where unsolidified yttrium oxide appears. Additionally, due to Y4Zr3O 12 Since the main peaks of the tetragonal and cubic crystal systems are located close to each other, the area intensity of each main peak can be calculated by peak separation.

4. The zirconia pre-fired body according to claim 1 or 2, wherein, The content of yttrium oxide relative to the total molar content of zirconium oxide and yttrium oxide is more than 2.5 mol% and less than 10 mol%.

5. Zirconia pre-sintered body, comprising zirconium oxide and yttrium oxide, When comparing the first translucency of a first sintered body prepared by calcining the zirconia pre-sintered body at 1550°C for 7 minutes at a heating rate of 350°C / min with the second translucency of a second sintered body prepared by calcining the zirconia pre-sintered body at 1550°C for 120 minutes at a heating rate of 10°C / min, The first light transmittance is more than 85% of the second light transmittance.

6. The method for manufacturing a zirconia pre-fired body according to claim 1 or 2, comprising: A process for manufacturing a zirconium oxide composition comprising zirconium oxide particles and yttrium oxide particles; A pulverizing process for pulverizing the 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 molded body. In the 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 is more than 40 hours.

7. The method for manufacturing a zirconia pre-fired body according to claim 6, wherein, The pre-firing temperature in the pre-firing process is 600~1300℃.

8. A zirconia sintered body comprising zirconia and a stabilizer capable of inhibiting zirconia phase transformation, wherein at least one zirconia crystal grain in the zirconia sintered body has a portion having a concentration gradient of the stabilizer in the same crystal grain that gradually decreases from the center side of the grain toward the grain boundary.

9. The zirconia sintered body according to claim 8, wherein, The concentration gradient is 0.1 to 3 mol relative to the total molar of zirconium oxide and stabilizer.

10. The zirconia sintered body according to claim 8 or 9, wherein, The stabilizer that can suppress the zirconium oxide phase transformation is yttrium oxide.

11. A zirconia sintered body comprising zirconia and a stabilizer capable of inhibiting the zirconia phase transformation, said zirconia sintered body comprising: The stabilizer content is 4-6 mol% (L) of zirconium oxide crystalline particles relative to the total molar percentage of zirconium oxide and stabilizer; and The stabilizer content is 1-3 mol% of zirconium oxide crystal particles (S) relative to the total molarity of zirconium oxide and stabilizer.

12. The zirconia sintered body according to claim 11, wherein, The average grain diameter of the zirconium oxide crystals (L) is in the range of 0.5~2.0 μm. The average grain diameter of the zirconium oxide crystal particles (S) is in the range of 0.1~0.3 μm.

13. The zirconia sintered body according to claim 11 or 12, wherein, The stabilizer that can suppress the zirconium oxide phase transformation is yttrium oxide.

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