Zirconia calcined body and method for producing same

Abstract

The present invention provides: a zirconia calcined body with which a zirconia sintered body exhibits excellent translucency even if obtained by being held at a maximum sintering temperature for 2 minutes; and a method for producing same. The present invention relates to a zirconia calcined body which contains zirconia as a component, contains yttria, and contains Y4Zr3O12 as a crystal system. In the zirconia calcined body, the abundance fd (%) of Y4Zr3O12, as calculated using formula (1-1), is preferably 2.5% or more.　fd (%)=I d / (Im+It+Ic+Iy+Id)×100 (1-1) (Explanations of symbols in the formula are omitted)

Description

Zirconia calcined body and its manufacturing method

[0001] The present invention relates to a zirconia calcined body and a method for producing the same. More specifically, the present invention relates to a zirconia calcined body that has excellent translucency even when the holding time at the maximum sintering temperature is 2 minutes, and a method for producing the same.

[0002] Zirconia sintered bodies are widely used industrially, and in particular, in recent years have been used as dental materials for dental prostheses, etc. These dental prostheses are often produced by forming a zirconia molded body having a desired shape, such as a disk or a prism, by press-molding zirconia particles or by molding using a composition containing zirconia particles, and then calcining this to form a calcined body (mill blank), which is then cut (milled) into the shape of the desired dental prosthesis and further fired.

[0003] Zirconia is a compound that undergoes phase transitions between multiple crystal systems. Therefore, partially stabilized zirconia (PSZ) and fully stabilized zirconia (FSZ), which are formed by dissolving a stabilizer such as yttria (yttrium oxide; YO) in zirconia to suppress the phase transition, are used in various fields.

[0004] In the dental field, zirconia materials have been used as frame materials due to their high strength but low translucency. In recent years, however, as the translucency of zirconia materials has improved, dental prostheses are increasingly being made solely from zirconia.

[0005] Traditionally, dental prostheses made solely from zirconia have often been fabricated in dental laboratories, meaning patients could not receive treatment using the dental prosthesis on the same day they visited the dental clinic, and had to return to the clinic on another day to receive treatment using the dental prosthesis.

[0006] In response to this, a one-visit treatment has been proposed in which a dental prosthesis can be easily fabricated at a dental clinic, allowing treatment using the dental prosthesis to be performed in a single visit to the clinic. In this case, zirconia needs to be fired in a short period of time, and a method for firing the zirconia has been proposed, such as in Patent Document 1.

[0007] International Publication No. 2018 / 056330

[0008] The method of Patent Document 1 shows that a sintered body produced by firing a calcined body at a maximum sintering temperature of 1550°C for 15 minutes can have the same translucency as a sintered body fired at the same temperature for 120 minutes, thereby shortening the firing time.

[0009] However, the present inventors have found that in the invention of Patent Document 1, when the holding time at the maximum sintering temperature of 1550°C is further shortened (for example, to 7 minutes or less), the translucency decreases. Therefore, it has been found that there is room for improvement in the invention of Patent Document 1 to further shorten the holding time.

[0010] An object of the present invention is to provide a zirconia calcined body that is excellent in translucency even when the holding time at the maximum sintering temperature is 2 minutes, and a method for producing the same. Another object of the present invention is to provide a zirconia sintered body that is excellent in translucency even when using a production method in which the holding time at the maximum sintering temperature when firing the zirconia calcined body is 2 minutes.

[0011] As a result of extensive research into solving the above problems, the present inventors have discovered a composite material containing zirconia, yttria, and a Y4Zr3O crystal system. 12 The present inventors have found that by forming a zirconia calcined body containing the above, the zirconia sintered body obtained has excellent translucency even when the holding time at the maximum sintering temperature is 2 minutes, and have conducted further research based on this finding, which has led to the completion of the present invention.

[0012] The present invention includes the following inventions: [1] Zirconia, yttria, and a Y4Zr3O crystal system 12[2] A zirconia calcined body containing Y4Zr3O calculated by the following formula (1-1): 12 The probability of occurrence f d The zirconia calcined body according to [1], wherein (%) is 2.5% or more. d (%) = I d / (I m +I t +I c +I y +I d )×100 (1-1) (where f d is Y4Zr3O 12 In XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d is Y4Zr3O 12 represents the area intensity of the peak at 2θ=29.6° where the peak top of the main peak of y represents the integrated intensity of the peak near 2θ = 29.2° where the peak top of the main peak of undissolved yttria appears. 12 [3] The zirconia contains monoclinic zirconia, and the monoclinic ratio f calculated by the following formula (1-2) is m (%) is less than 55%. m (%) = I m / (I m +I t +I c +I y +I d )×100 (1-2) (where f m represents the monoclinic crystal ratio (%), and in the XRD measurement, I mrepresents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d is Y4Zr3O 12 represents the area intensity of the peak at 2θ=29.6° where the peak top of the main peak of y represents the integrated intensity of the peak near 2θ = 29.2° where the peak top of the main peak of undissolved yttria appears. 12(Because the positions of the main peaks of the tetragonal, tetragonal, and cubic systems are similar, the area intensity of each main peak is calculated by peak separation.) [4] A zirconia calcined body according to any one of [1] to [3], wherein the content of yttria is 2.5 mol % or more and 10 mol % or less with respect to the total moles of zirconia and yttria. [5] A zirconia calcined body containing zirconia and yttria, wherein, when a first translucency of a first sintered body produced by firing the zirconia calcined body at 1550°C for 7 minutes at a heating rate of 350°C / min is compared with a second translucency of a second sintered body produced by firing the zirconia calcined body at 1550°C for 120 minutes at a heating rate of 10°C / min, the first translucency is 85% or more of the second translucency. [6] A method for producing a zirconia calcined body according to any one of [1] to [5], comprising: a step of producing a zirconia composition containing zirconia particles and yttria particles; a grinding step of grinding the zirconia composition; a molding step of molding the ground zirconia composition to obtain a green body; and a calcining step of calcining the green body, wherein the grinding step (i) uses grinding media with a diameter of less than 1 mm and the grinding time is 10 minutes or more, or (ii) uses grinding media with a diameter of 1 mm or more and the grinding time is more than 40 hours. [7] A method for producing a zirconia calcined body according to [6], wherein the calcination temperature in the calcining step is 600 to 1300°C. [8] A zirconia sintered body comprising zirconia and a stabilizer capable of suppressing a phase transition of zirconia, wherein at least one zirconia crystal grain contained in the zirconia sintered body has a portion having a concentration gradient in which the concentration of the stabilizer in the same crystal grain decreases from the center of the crystal grain toward the outer grain boundary. [9] The zirconia sintered body according to [8], wherein the concentration gradient is 0.1 to 3 mol% relative to the total moles of zirconia and the stabilizer.

[10] The zirconia sintered body according to [8] or [9], wherein the stabilizer capable of suppressing the phase transition of zirconia is yttria.

[11] A zirconia sintered body comprising zirconia and a stabilizer capable of suppressing a phase transition of zirconia, the zirconia sintered body comprising: zirconia crystal particles (L) having a stabilizer content of 4 to 6 mol % relative to the total moles of zirconia and the stabilizer; and zirconia crystal particles (S) having a stabilizer content of 1 to 3 mol % relative to the total moles of zirconia and the stabilizer.

[12] The zirconia sintered body according to

[11] , wherein the zirconia crystal particles (L) have an average crystal particle size in the range of 0.5 to 2.0 μm, and the zirconia crystal particles (S) have an average crystal particle size in the range of 0.1 to 0.3 μm.

[13] The zirconia sintered body according to

[11] or

[12] , wherein the stabilizer capable of suppressing a phase transition of zirconia is yttria.

[0013] According to the present invention, a zirconia calcined body and a method for producing the same can be provided, which exhibit excellent translucency even when the holding time at the maximum sintering temperature is 2 minutes. Furthermore, by using the zirconia calcined body and zirconia composition of the present invention and their methods for producing the same, a zirconia sintered body can be obtained that maintains high translucency equivalent to that obtained when sintered for a long period of time, such as 7 minutes or less, after sintering at 1550°C. This contributes to further improvement in productivity, such as shortening treatment time at dental clinics, and is advantageous for realizing one-visit treatment at dental clinics. Furthermore, by using the zirconia calcined body and zirconia composition of the present invention and their methods for producing the same, a zirconia sintered body exhibiting excellent mechanical strength and translucency can be obtained at a lower maximum sintering temperature (e.g., 1450°C or lower) than conventionally possible. Furthermore, the present invention can provide a zirconia sintered body exhibiting excellent translucency even when produced by a production method in which the holding time at the maximum sintering temperature during firing of the zirconia calcined body is 2 minutes. Furthermore, the present invention can provide a zirconia sintered body having excellent mechanical strength even when produced by a production method in which the holding time at the maximum sintering temperature when firing the zirconia calcined body is 2 minutes.

[0014] 1 is an electron beam diffraction image for explaining a method for calculating the distance and angle of a diffraction spot. 2 is a result of observing the zirconia sintered body according to the present invention with a transmission electron microscope (TEM).

[0015] [Zirconia Calcined Body] The zirconia calcined body of the present invention is a zirconia calcined body containing zirconia, yttria, and Y4Zr3O as a crystal system. 12 In other words, the present invention provides a zirconia calcined body containing zirconia and yttria as components, and having a crystal system of Y4Zr3O 12 The present invention relates to a zirconia calcined body comprising:

[0016] In this specification, "Y4Zr3O 12 " is a metastable crystal system of zirconia present in zirconia calcined bodies. 12is known to exist up to around 1375°C on a phase diagram. In this specification, "zirconia composition" refers to a composition containing zirconia powder and yttria powder. In this specification, "molded body" refers to a body that has not reached either a semi-sintered state (calcined state) or a sintered state. In other words, a molded body is distinguished from a calcined body and a sintered body in that it is a body that has been formed by molding and then not sintered. In this specification, "zirconia calcined body" refers to a body in a semi-sintered state in which zirconia particles are necked (adhered) to each other and the zirconia particles are not completely sintered. In this specification, "zirconia sintered body" refers to a body in a sintered state in which the zirconia particles are completely sintered. In a zirconia sintered body, the zirconia particles solidify together through sintering, and the relative density increases and densification progresses, resulting in a completely sintered state in which the relative density is 95% or more. In this specification, "zirconia" refers to zirconium (IV) oxide (ZrO), and ZrO particles contain a trace amount of HfO relative to the amount of ZrO (0.5% by mass to 3% by mass). Because HfO is difficult to separate, terms such as "zirconia," "zirconia particles," and "zirconia powder" refer to materials containing both ZrO and HfO. Furthermore, particles and powders in which yttria is solid-dissolved in zirconia are also included in the terms "zirconia particles" and "zirconia powder," respectively. In this specification, "atmospheric pressure" refers to standard atmospheric pressure (1 atm). In this specification, the upper and lower limits of numerical ranges (such as temperature ranges, content rates of each component, abundance rates of crystalline systems, values ​​calculated from components, and each physical property) can be combined as appropriate.

[0017] In one preferred embodiment, Y4Zr3O calculated by the following formula (1-1) 12 The probability of occurrence f d (%) is 2.5% or more. d (%) = I d / (I m +I t +I c +I y +I d )×100 (1-1) (where fd is Y4Zr3O 12 In XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d is Y4Zr3O 12 represents the area intensity of the peak at 2θ=29.6° where the peak top of the main peak of y represents the integrated intensity of the peak near 2θ = 29.2° where the peak top of the main peak of undissolved yttria appears. 12 Since the positions of the main peaks of the tetragonal and cubic crystal systems are similar, the area intensity of each main peak is calculated by peak separation.)

[0018] Y4Zr3O in the zirconia calcined body according to the preferred embodiment 12 The probability of occurrence f d (%) is preferably 3.0% or more, more preferably 4.0% or more, even more preferably 5.0% or more, particularly preferably 6.0% or more, and is most preferably 6.5% or more, from the viewpoint that the zirconia sintered body obtained is excellent in translucency even when the holding time at the highest sintering temperature is 2 minutes, or that high translucency equivalent to that of long-term sintering is easily maintained after sintering for a short time of 7 minutes or less at 1550°C. 12 The probability of occurrence f d (%) is Y4Zr3O 12 Since the phase transition from Y4Zr3O to another crystal system becomes the rate-determining step and the sintering of the zirconia calcined body becomes difficult to proceed, the content is preferably 30% or less, more preferably 25% or less, even more preferably 22% or less, and particularly preferably 20% or less. 12 The probability of occurrence f dThe calculation method for (%) can be performed using the above formula (1-1). 12 The probability of occurrence f d The method for measuring (%) is as described in the Examples below.

[0019] The zirconia calcined body of the present invention has a crystal system of Y4Zr3O 12 (particularly preferably, the abundance f d The reason why the zirconia sintered body obtained by the above-mentioned method (where Y4Zr3O is a predetermined ratio) has excellent translucency even when the holding time at the highest sintering temperature is 2 minutes, and why the high translucency equivalent to that of the long-term sintering can be maintained after sintering for a short time of 7 minutes or less at 1550°C, is not clear, but it is presumed as follows. 12 By including the compound, the degree of uneven distribution of yttrium atoms in the calcined body is reduced, and the state of yttrium atoms in the calcined body before sintering approaches the final state of existence of yttrium atoms in the sintered body, thereby shortening the distance that yttrium atoms move toward the zirconia during firing. As a result, the heat energy required during firing is reduced, and it is thought that a sintered body having the same level of translucency can be obtained even when fired for a shorter time than in conventional techniques.

[0020] The zirconia calcined body contains yttria (Y2O3) as a stabilizer capable of suppressing the phase transition of zirconia. In this specification, the yttria contained as a component in the zirconia calcined body does not necessarily have to exist as Y2O3 alone, but may exist in a state containing yttrium element (for example, Y4Zr3O 12 etc.), and yttria does not necessarily have to be detected as Y2O3 crystals.

[0021] The yttria content in the zirconia calcined body is preferably 2.5 mol% or more, more preferably 3.0 mol% or more, even more preferably 3.5 mol% or more, and particularly preferably 4.0 mol% or more, based on the total moles of zirconia (zirconium (IV) oxide; ZrO2) and yttria. A content of 2.5 mol% or more is preferable in that the crystal system contained in the sintered body contains more cubic systems, thereby improving translucency. Furthermore, the yttria 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. A yttria content of 10 mol% or less is preferable in that it prevents a decrease in mechanical strength. The stabilizer content of the zirconia calcined body of the present invention can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis, or the like.

[0022] The zirconia calcined body of the present invention may contain only yttria as the stabilizer capable of suppressing the phase transition of zirconia, or may further contain a stabilizer other than yttria that can suppress the phase transition of zirconia. Examples of stabilizers other than yttria that can suppress the phase transition of zirconia (hereinafter simply referred to as "stabilizers") include calcium oxide (CaO), magnesium oxide (MgO), cerium oxide (CeO), scandium oxide (ScO), niobium oxide (NbO), lanthanum oxide (LaO), erbium oxide (ErO), praseodymium oxide (PrO, PrO) and the like. 11 Examples of the stabilizer include oxides such as samarium oxide (SmO), europium oxide (EuO), thulium oxide (TmO), gallium oxide (GaO), indium oxide (InO), and ytterbium oxide (YbO). One of the stabilizers may be used alone, or two or more of them may be used in combination.

[0023] The zirconia calcined body of the present invention is Y4Zr3O 12In addition, the zirconia contains monoclinic zirconia, and the monoclinic fraction f calculated by the formula (1-2) is preferably 0.01 to 0.01. Since the zirconia has excellent translucency even when held at the highest sintering temperature for a shorter period of time (for example, 2 minutes), the zirconia is m (%) is preferably less than 55%. m (%) = I m / (I m +I t +I c +I y +I d )×100 (1-2) (where f m represents the monoclinic crystal ratio (%), and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the peak top of the monoclinic main peak appears, and I t represents the area intensity of the peak near 2θ = 30.3° where the peak top of the main peak of the tetragonal system appears, and I c represents the area intensity of the peak near 2θ = 30.0° where the peak top of the main peak of the cubic crystal system appears, and I d is Y4Zr3O 12 represents the area intensity of the peak at 2θ=29.6° where the peak top of the main peak of y represents the integrated intensity of the peak near 2θ = 29.2° where the peak top of the main peak of undissolved yttria appears. 12 Since the positions of the main peaks of the tetragonal and cubic crystal systems are similar, the area intensity of each main peak is calculated by peak separation.)

[0024] Monoclinic ratio f m (%) is Y4Zr3O 12 The monoclinic fraction f is more preferably 48% or less, further preferably 46% or less, and particularly preferably 45% or less, in view of the fact that the zirconia sintered body obtained by integrally acting with the monoclinic fraction f is excellent in light transmittance even when the holding time at the maximum sintering temperature is 2 minutes. m(%) is preferably 5% or more, more preferably 10% or more, even more preferably 15% or more, and particularly preferably 20% or more. 12 In addition, the crystal system is Y4Zr3O because it has excellent light transmittance even when the maximum sintering temperature is maintained for a shorter time (for example, 2 minutes). 12 and the monoclinic ratio f m The zirconia calcined body in the above embodiment has a monoclinic fraction f (%) of 0% or more and less than 5%. m There are no particular limitations on the zirconia content as long as the zirconia content is 0% or more and less than 5%, and examples thereof include tetragonal zirconia and cubic zirconia.

[0025] The zirconia calcined body of the present invention may contain additives other than zirconia and stabilizers, such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (AlO), titanium oxide (TiO), and silica (SiO), as long as the effects of the present invention are achieved.

[0026] Examples of the pigment include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically, NiO, CrO, etc.) (however, YO and CeO are excluded). An oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb is preferred, and an oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb is more preferred. The zirconia calcined body of the present invention may also be free of erbium oxide (Er2O3). Examples of the composite pigment include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4.ZrSiO4, and (Co,Zn)Al2O4. Examples of the fluorescent agent include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl2O4. 10 O 17 : Eu, etc.

[0027] The zirconia calcined body of the present invention may contain a fluorescent agent. By including a fluorescent agent in the zirconia calcined body, the zirconia sintered body has fluorescence. The type of fluorescent agent is not particularly limited, and one or more fluorescent agents capable of emitting fluorescence with light of any wavelength can be used. Examples of fluorescent agents include those containing metal elements. Examples of such metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one of these metal elements alone, or two or more of them. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred. Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the above metal elements. The fluorescent agents are Y2SiO5:Ce, Y2SiO5:Tb, (Y, Gd, Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl.10 O 17 :Eu, etc.

[0028] The content of the fluorescent agent in the zirconia calcined body is not particularly limited and can be adjusted appropriately depending on the type of fluorescent agent or the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the fluorescent agent content is preferably 0.001 mass% or more, more preferably 0.005 mass% or more, and even more preferably 0.01 mass% or more, calculated as the oxide of the metal element contained in the fluorescent agent, relative to 100 mass% of zirconia contained in the zirconia calcined body. Furthermore, the fluorescent agent content is not limited, as long as suitable fluorescence is exhibited, and may be 1 mass% or less, 0.5 mass% or less, or even 0.1 mass% or less. When the content is equal to or greater than the lower limit, the fluorescence is comparable to that of natural human teeth. When the content is equal to or less than the upper limit, the decrease in translucency and mechanical strength can be suppressed.

[0029] The zirconia calcined body of the present invention has excellent translucency even when the holding time at 1550°C is 7 minutes or less (for example, 2 minutes). A sintered body produced by firing a zirconia calcined body at 1550°C for 7 minutes at a heating rate of 350°C / min is referred to as a first sintered body. Furthermore, a sintered body produced by firing a zirconia calcined body of the same size as the zirconia calcined body used to produce the first sintered body at 1550°C for 120 minutes at a heating rate of 10°C / min is referred to as a second sintered body. A preferred embodiment of the present invention is a zirconia calcined body containing zirconia and yttria, wherein, when a first translucency of a first sintered body produced by firing the zirconia calcined body at 1550°C for 7 minutes at a heating rate of 350°C / min is compared with a second translucency of a second sintered body produced by firing the zirconia calcined body at 1550°C for 120 minutes at a heating rate of 10°C / min, the first translucency is 85% or more of the second translucency.

[0030] When the first sintered body is produced by firing at 1550°C for 7 minutes, and the translucency of the first sintered body is compared with that of the second sintered body, the translucency of the first sintered body is preferably 85% or more of that of the second sintered body, more preferably 90% or more, even more preferably 95% or more, and particularly preferably substantially equal. As described above, the zirconia calcined body of the present invention has the advantages of short-time firing of 7 minutes or less. Details of the method for measuring the translucency will be described later in the examples. Furthermore, a zirconia calcined body according to another preferred embodiment of the present invention is a zirconia calcined body containing zirconia, yttria, and Y4Zr3O 12 and the light transmittance of the first sintered body is within the above-mentioned preferred range (for example, 85% or more) relative to the light transmittance of the second sintered body.

[0031] The flexural strength of the zirconia calcined body of the present invention is preferably 15 MPa or more to ensure mechanical strength that allows mechanical processing in the calcined body state, and is preferably 70 MPa or less, more preferably 60 MPa or less, to facilitate mechanical processing in the calcined body state.

[0032] The bending strength can be measured in accordance with ISO 6872:2015 (Dentistry - Ceramic materials), but the only change is the size of the test specimen, which is measured using a test specimen measuring 5 mm x 10 mm x 50 mm. The test specimen's face and C-face (the surface where the corners of the test specimen are chamfered at a 45° angle) are finished in the longitudinal direction with 600-grit sandpaper. The test specimen is positioned so that the widest surface faces vertically (load direction). In the three-point bending test, the support distance (span) is 30 mm and the crosshead speed is 0.5 mm / min.

[0033] The density of the zirconia calcined body of the present invention is 2.7 g / cm 3 More preferably, 3.0 g / cm 3 More preferably, it is 3.2 g / cm or more. 3 It is more preferable that the density of the zirconia calcined body is 4.0 g / cm or more.3 Preferably, 3.8 g / cm or less 3 More preferably, 3.6 g / cm 3 The following is even more preferable: When the density is within the above range, molding can be easily carried out.

[0034] The density of the zirconia calcined body can be calculated by (mass of the zirconia calcined body) / (volume of the zirconia calcined body). The density of the zirconia calcined body can be calculated, for example, by cutting out 10 mm square specimens (n=3) from arbitrary positions on the zirconia calcined body while changing the cutting position, measuring the mass and volume of the obtained specimens, calculating the arithmetic mean value of the measured values, and using the arithmetic mean value to calculate the density according to the above formula.

[0035] [Method for Producing Zirconia Calcined Body] Next, a method for producing a zirconia calcined body will be described. The zirconia calcined body of the present invention can be produced by pulverizing a zirconia composition, molding the pulverized zirconia composition into a molded body, and firing (calcining) the molded body to an extent that the zirconia particles do not sinter together, and applying excess energy to the pulverization process under predetermined conditions compared to conventional techniques. Examples of a method for producing a zirconia calcined body of the present invention include a step of producing a zirconia composition containing zirconia particles and yttria particles, a pulverization step of pulverizing the zirconia composition, a molding step of molding the pulverized zirconia composition to obtain a molded body, and a calcination step of calcining the molded body, wherein the pulverization step includes a predetermined pulverization process described below.

[0036] The zirconia composition can be produced by mixing raw material powders, zirconia powder and yttria powder, using any known method and apparatus without any particular limitations.

[0037] As a method for preparing the zirconia particles constituting the zirconia powder and the yttria particles constituting the yttria powder, for example, a breakdown process in which coarse particles are pulverized or crushed to form fine powder, or a building-up process in which atoms or ions are synthesized through a nucleation and growth process can be employed.

[0038] The zirconia constituting the zirconia powder is not particularly limited, and any of tetragonal zirconia, monoclinic zirconia, and cubic zirconia can be used. In the zirconia powder, these may be used alone or in combination of two or more.

[0039] As the zirconia powder, commercially available zirconia particles may be used, or the commercially available powder may be used after being pulverized in a known pulverizing / mixing device (such as a ball mill).As the yttria powder, commercially available yttria particles may be used, or the commercially available powder may be used after being pulverized in a known pulverizing / mixing device (such as a ball mill).

[0040] Commercially available zirconia powders include, for example, zirconia powders (trade names "Zpex (registered trademark)" (Y2O3 content: 3 mol%), "Zpex (registered trademark) 4" (Y2O3 content: 4 mol%), and "Zpex (registered trademark) Smile (registered trademark)" (YO content: 5.5 mol%), "TZ-3Y" (YO content: 3 mol%), "TZ-3YS" (YO content: 3 mol%), "TZ-4YS" (YO content: 4 mol%), "TZ-6Y" (YO content: 6 mol%), "TZ-6YS" (YO content: 6 mol%), "TZ-8YS" (YO content: 8 mol%), "TZ-10YS" (YO content: 10 mol%), "TZ-3Y-E" (YO content: 3 mol%), "TZ- Examples of such zirconia include "TZ-3YS-E" (YO content: 3 mol%), "TZ-3YB-E" (YO content: 3 mol%), "TZ-3YSB-E" (YO content: 3 mol%), "TZ-3YB" (YO content: 3 mol%), "TZ-3YSB" (YO content: 3 mol%), "TZ-3Y20AB" (YO content: 3 mol%), "TZ-8YSB" (YO content: 8 mol%), and "TZ-0" (YO content: 0 mol%; monoclinic zirconia); all manufactured by Tosoh Corporation.

[0041] Next, the zirconia composition is further pulverized. By applying excess energy compared to the prior art in the pulverization process under predetermined conditions, the zirconia composition is calcined to produce Y4Zr3O 12 A zirconia composition that produces the formula (I) is obtained. Conventionally, since zirconia particles are a substance with extremely high hardness, even if the amount of energy in the pulverization treatment is increased, it is difficult to make the zirconia particles excessively small. From this viewpoint, there has been no technical significance in carrying out an excessive pulverization treatment. However, in the present invention, when a zirconia composition containing zirconia and yttria is subjected to a pulverization treatment and the energy in the pulverization treatment is applied in excess of that in the conventional technique, that is, when the zirconia composition contains both zirconia and yttria and the pulverization treatment is carried out with the energy applied in excess of that in the conventional technique, the calcined body produced is Y4Zr3O 12 It is presumed that by producing the above, excellent translucency can be exhibited even when the holding time at the maximum sintering temperature is 2 minutes.

[0042] In the grinding process, it is preferable to use the following methods: (i) grinding media with a diameter of less than 1 mm, or (ii) grinding media with a diameter of 1 mm or more, with a grinding time of more than 40 hours.

[0043] When using grinding media with a diameter of less than 1 mm, the grinding media diameter (diameter) is set to be small, so that when the calcined body is produced, the Y4Zr3O 12 Since the diameter of the grinding media is easily generated, a diameter of 0.1 to 0.5 mm is preferred. Commercially available grinding media with a diameter of less than 1 mm may be used. Examples of grinding devices using grinding media with a diameter of less than 1 mm include bead mills.

[0044] When using grinding media with a diameter of less than 1 mm, the grinding time is not particularly limited. However, when the calcined body is produced, the Y4Zr3O 12is easily generated, the time is preferably 10 minutes or more, more preferably 15 minutes or more, and even more preferably 20 minutes or more. The time for the grinding treatment 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. When a grinding device that grinds while circulating the slurry (for example, a circulating bead mill) is used as the grinding device, the grinding time refers to the residence time of the slurry in the vessel (grinding chamber).

[0045] When using grinding media with a diameter of 1 mm or more, the grinding media diameter (diameter) is preferably 1.5 mm or more, and more preferably 2.0 mm or more, because this makes it easier to increase the amount of energy required for the grinding process by increasing the grinding time. Commercially available grinding media with a diameter of 1 mm or more may be used. Examples of grinding devices that use grinding media with a diameter of 1 mm or more include ball mills.

[0046] When using grinding media with a diameter of 1 mm or more, the grinding time (grinding treatment time) is not particularly limited, but is preferably more than 40 hours, and more preferably 55 hours or more. This makes it easier to grind yttria particles to a very small size, and when a calcined body is produced, Y4Zr3O 12 The probability of occurrence f d In order to easily increase the solubility of the powder, the time is more preferably 80 hours or more, and particularly preferably 100 hours or more. The time for the grinding treatment 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.

[0047] In the present invention, by supplying increased milling energy to the zirconia composition by adjusting the combination of the milling time and the milling media diameter, it is possible to obtain Y4Zr3O when calcined. 12 A zirconia composition can be obtained that produces

[0048] By using the zirconia composition obtained as described above to which excessive grinding energy has been applied, the zirconia calcined body of the present invention can be produced as a zirconia having a crystal system of Y4Zr3O 12 It is presumed that this makes it easier to adjust the ratio to a specified ratio that provides a more effective effect.

[0049] The zirconia composition may be in the form of granules, a slurry, etc. When the zirconia composition is a slurry, the slurry can be produced by mixing the mixed powder obtained by the pulverization treatment with a solvent (preferably water).

[0050] The average particle size of the zirconia composition after the pulverization treatment is preferably 0.2 μm or less, since the sintered body has excellent light transmittance even when the holding time at the maximum sintering temperature is 2 minutes.

[0051] The average particle size of the zirconia particles and yttria particles in the zirconia composition after the pulverization treatment can be measured by a dynamic light scattering particle size distribution measurement method. For example, using a dynamic light scattering particle size distribution measurement device (product name "SZ-100V2") manufactured by Horiba, Ltd., a slurry diluted to about 0.1 mass % with water is irradiated with ultrasonic waves for 30 minutes, and then the average particle size can be measured on a volume basis while applying ultrasonic waves.

[0052] The zirconia composition may also contain additives such as binders, dispersants, emulsifiers, antifoaming agents, pH adjusters, lubricants, and light transmittance adjusters. The additives may be used alone or in combination of two or more. Examples of binders include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.

[0053] In order to improve translucency, the content of the binder in the zirconia composition of the present invention is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less, relative to 100% by mass of zirconia.

[0054] Examples of the plasticizer include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0055] Examples of dispersants include ammonium polycarboxylate (e.g., triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic acid ester copolymer, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (e.g., polyoxyethylene alkyl ether phosphate esters such as polyoxyethylene lauryl ether phosphate esters), nonionic surfactants, olein glyceride, amine salt surfactants, oligosaccharide alcohols, and stearic acid.

[0056] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitan derivatives.

[0057] Examples of the antifoaming agent include alcohol, polyether, polyethylene glycol, silicone, and wax.

[0058] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide).

[0059] Examples of the lubricant include polyoxyethylene alkyl ether and wax.

[0060] Examples of the light transmittance adjusting agent include aluminum oxide (Al2O3), titanium oxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0061] The BET specific surface area of ​​the particles constituting the zirconia composition is 7.0 m when measured in accordance with JIS Z 8830:2013. 2 / g or more, and 7.5m 2 / g or more, and more preferably 8.0m 2 / g or more is more preferable. 2 / g or more, the sintered body can be prevented from becoming cloudy when sintered. 2 / g or less, and 2 / g or less is more preferable, and 40m 2 / g or less is more preferable. 2 / g or less, the BET specific surface area is less susceptible to temperature variations in the firing furnace. The BET specific surface area can be measured using a commercially available product such as a fully automatic specific surface area measuring device (trade name "Macsorb (registered trademark) HM model-1200", BET flow method (single-point method / multi-point method), manufactured by Mountec Co., Ltd.). For example, it can be measured by the BET flow method (single-point method) using the fully automatic specific surface area measuring device. Furthermore, even when the firing time for sintering is shortened, the light transmittance of the sintered body is less likely to decrease. The "BET specific surface area" referred to here is a specific surface area measured without distinguishing between primary particles and secondary particles.

[0062] Next, the pulverized zirconia composition is subjected to a molding step to produce a molded body, which is obtained by applying an external force to the zirconia composition using a known method.

[0063] The molding method is not particularly limited, and the following methods can be used, for example: (a) a step of slip-casting a slurry containing the pulverized zirconia composition; (b) a step of gel-casting a slurry containing the pulverized zirconia composition; (c) a step of press-molding the pulverized zirconia composition; (d) a step of molding a zirconia composition containing zirconia particles, yttria particles, and a resin; (e) a step of polymerizing a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer; and (f) a step of additive manufacturing of granules containing zirconia particles and yttria particles.

[0064] (a) Slip Casting When a zirconia molded body is produced by a method including a step of slip-casting a slurry containing a zirconia composition after a pulverization treatment, the specific slip-casting method is not particularly limited. For example, a method in which the slurry is poured into a mold and then dried can be employed. 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, because this facilitates pouring the slurry into the mold, prevents the drying process from taking a long time, and allows the mold to be used more frequently. The slurry may be poured into the mold under normal pressure, but from the viewpoint of production efficiency, it is preferable to pour the slurry into the mold under pressurized conditions.

[0065] (b) Gel Casting When a zirconia molded body is produced by a method including a step of gel-casting a slurry containing a zirconia composition after a pulverization treatment, the specific gel-casting method is not particularly limited. For example, a method can be employed in which the slurry is gelled in a mold to obtain a shaped wet body, and then this is dried. 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, in order to prevent a long drying time and to suppress the occurrence of cracks during drying. Gelation can be carried out, for example, by adding a gelling agent or by adding a polymerizable monomer and then polymerizing it.

[0066] There is no limitation on the type of gelling agent, and for example, a water-soluble gelling agent can be used, and specifically, agarose, gelatin, etc. can be preferably used. A single gelling agent may be used alone, or two or more types may be used in combination. The amount of gelling agent used is not particularly limited as long as problems such as cracking do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less based on the mass of the slurry after the gelling agent is blended.

[0067] The type of polymerizable monomer is not particularly limited, and examples thereof 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, N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N,N-bis(2-hydroxyethyl) (meth)acrylamide. One type of polymerizable monomer may be used alone, or two or more types may be used in combination. The amount of polymerizable monomer used is not particularly limited as long as problems such as cracking do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less, based on the mass of the slurry after the polymerizable monomer is blended.

[0068] When gelation is carried out by polymerization of a polymerizable monomer, the polymerization is preferably carried out using a polymerization initiator. There are no particular restrictions on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred.

[0069] Specific examples of the photopolymerization initiator include (bis)acylphosphine oxides (including salts), thioxanthones (including salts such as quaternary ammonium salts), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ether compounds, and α-aminoketone compounds. One photopolymerization initiator may be used alone, or two or more may be used in combination. Among these photopolymerization initiators, it is preferable to use at least one selected from the group consisting of (bis)acylphosphine oxides and α-diketones. This allows polymerization (gelation) to occur in both the ultraviolet (including near-ultraviolet) and visible light regions, and in particular, polymerization (gelation) can be sufficiently performed using any light source, such as a laser (e.g., Ar laser, He—Cd laser), or lighting (e.g., halogen lamp, xenon lamp, metal halide lamp, light-emitting diode (LED), mercury lamp, or fluorescent lamp.

[0070] The drying method for drying the shaped wet body is not particularly limited, and examples thereof include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. These may be used alone or in combination. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred because they can suppress the occurrence of cracks during drying.

[0071] There are no particular limitations on the type of mold used in slip casting and gel casting, and for example, porous molds made of plaster, resin, ceramics, etc., and non-porous molds made of metal, resin, etc. can be used.

[0072] (c) Press Molding In the step of press molding the zirconia composition after the pulverization treatment, the specific press molding method is not particularly limited, and can be performed using a known press molding machine. Specific examples of the press molding method include uniaxial pressing.

[0073] Alternatively, multi-stage molding may be performed. For example, after press-molding the zirconia composition, a cold isostatic pressing (CIP) treatment may be further performed.

[0074] The shape of the molded body is not particularly limited and may be a disk, a rectangular parallelepiped, or a dental product shape (e.g., a crown shape). The molded body may be, for example, a columnar zirconia molded body obtained by filling a mold with a zirconia composition (e.g., granules) and compacting it with a uniaxial press. The higher the surface pressure in the press 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 calcined body will become hard. Therefore, the surface pressure in the press molding when producing the zirconia molded body is preferably 30 to 200 MPa. When the surface pressure in the press is 30 MPa or more, the shape retention of the zirconia molded body is excellent, and when it is 200 MPa or less, the density of the zirconia molded body does not increase too much, making it easier to prevent hardening.

[0075] The molded body also includes a molded body densified by a high-temperature pressure treatment such as CIP (Cold Isostatic Pressing). From the same viewpoint as above, the pressure of the CIP is preferably 30 to 200 MPa.

[0076] (d) Molding of a zirconia composition containing a resin When a zirconia molded body is produced by a method including a step of molding a zirconia composition containing zirconia particles, yttria particles, and a resin, the specific method for molding the zirconia composition is not particularly limited, and for example, injection molding, cast molding, extrusion molding, etc. can be used. Furthermore, a method of molding the composition by fusion dynamic molding (FDM), an inkjet method, a powder / binder lamination method, or other additive manufacturing methods (3D printing, etc.) may also be used. Among these molding methods, injection molding and cast molding are preferred, and injection molding is more preferred. The type of resin is not particularly limited, and it is preferable to use the binder described above.

[0077] (e) Polymerization of a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer. Polymerization of a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer polymerizes the polymerizable monomer or oligomer in the composition, thereby hardening the composition. When producing a zirconia molded body using a method including this polymerization step, the specific method is not particularly limited. For example, a method of polymerizing a zirconia composition in a mold or a stereolithography (SLA) method using a zirconia composition can be employed. Among these, the stereolithography (SLA) method (b) is preferred. Stereolithography allows the zirconia molded body to be given a shape corresponding to the desired shape of the final zirconia sintered body at the time of production. Therefore, stereolithography may be particularly suitable when the zirconia sintered body is used as a dental material for dental prostheses, etc. The type of polymerizable monomer is not particularly limited, and may be any of monofunctional polymerizable monomers such as monofunctional (meth)acrylates and monofunctional (meth)acrylamides, and polyfunctional polymerizable monomers such as bifunctional aromatic compounds, bifunctional aliphatic compounds, and trifunctional or higher compounds. One type of polymerizable monomer may be used alone, or two or more types may be used. Among these, it is preferable to use a polyfunctional polymerizable monomer, particularly when a stereolithography method is employed. The oligomer is not particularly limited as long as it is a compound in which two or more of the above polymerizable monomers are bonded and has polymerizability.

[0078] Examples of monofunctional (meth)acrylates include (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and sec-butyl (meth)acrylate. alkyl (meth)acrylates such as acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate; alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic group-containing (meth)acrylates such as benzyl (meth)acrylate and phenyl (meth)acrylate; and (meth)acrylates having a functional group such as 2,3-dibromopropyl (meth)acrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, and 11-(meth)acryloyloxyundecyltrimethoxysilane. 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.Among these monofunctional polymerizable monomers, (meth)acrylamide is preferred because of its excellent polymerizability, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.

[0079] Examples of the bifunctional aromatic compound 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, 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane, 2, Examples of (meth)acrylates include 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, and 1,4-bis(2-(meth)acryloyloxyethyl)pyromellitate. Among these, Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article. Of the 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propanes, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average number of moles of ethoxy groups added: 2.6, commonly known as "D-2.6E") is preferred.

[0080] Examples of the bifunctional aliphatic compounds include glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of (meth)acrylates include triethylene glycol dimethacrylate (TEGDMA) and UDMA, which are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0081] Examples of tri- or higher functional compounds include (meth)acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacryloyloxy-2,2,6,6-tetra(meth)acryloyloxymethyl-4-oxaheptane. Among these, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetramethacrylate and 1,7-diacryloyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxaheptane are preferred in terms of excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0082] In any of the above methods, the polymerization of the composition is preferably carried out using a polymerization initiator, and the composition preferably further contains a polymerization initiator. There are no particular limitations on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred. Specific examples of photopolymerization initiators are the same as those described above in the explanation of gel casting.

[0083] When a zirconia molded body is produced by stereolithography using a zirconia composition, the specific method of stereolithography is not particularly limited, and any known method can be appropriately employed for stereolithography. For example, a method can be employed in which a liquid composition is photopolymerized using an optical shaping device with ultraviolet light, a laser, or the like to sequentially form layers having a desired shape, thereby obtaining the desired zirconia molded body.

[0084] To further improve the density of the cured zirconia molded body, the zirconia molded body may be subjected to a humidification treatment followed by a CIP treatment. When press molding is performed, a powder containing zirconia particles may be humidified before press molding, followed by press molding. The humidification method may be any known method, including spraying water with a spray bottle or using a hygrostat or thermo-hygrostat. The moisture content of the humidification treatment varies depending on the average particle size of the zirconia particles and the average particle size of the stabilizer particles, but is preferably greater than 2% by mass, more preferably greater than 3% by mass, even more preferably greater than 4% by mass, and particularly preferably greater than 5% by mass, relative to the mass of the powder before humidification (powder before humidification treatment) and the molded body. It is also preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 11% by mass or less. The moisture content of the powder after humidification can be calculated as a percentage by subtracting the mass of the powder before humidification and the compact from the mass of the wet powder (powder after humidification) and the compact, and dividing the result by the mass of the powder before humidification and the compact. The pressure for the CIP treatment is the same as that described above in the description of press molding.

[0085] (f) Step of additive manufacturing of granules containing zirconia particles and yttria particles When manufacturing granules containing zirconia particles and yttria particles, there are no particular limitations on the specific method. For example, a method can be used in which the granules are slurried and then dried in a spray dryer to form granules, and the resulting granules can be used for powder additive manufacturing. There are no particular limitations on the powder additive manufacturing method, but examples include a powder bed method, an SLS method (selective laser sintering method), an SLM method (selective laser melting method), an electron beam method, an arc discharge method, and a binder jet method. For methods in which it is preferable to not use organic substances during additive manufacturing, it is preferable not to use organic substances even in the granule manufacturing stage.

[0086] Next, the compact is calcined in a calcination step to obtain the calcined zirconia body of the present invention.

[0087] The calcination temperature (maximum calcination temperature) in the calcination step is set to 1000 K. ... 12 In order to obtain the above-mentioned product and to ensure a semi-sintered state, the calcination 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. 12 From the viewpoint of obtaining a desired temperature and ensuring workability, the temperature is preferably 1300°C or lower, more preferably 1250°C or lower, even more preferably 1200°C or lower, and particularly preferably 1150°C or lower. That is, in the method for producing a zirconia calcined body of the present invention, the temperature is preferably 600 to 1300°C.

[0088] The holding time (holding time) at the maximum calcination temperature can be set to a semi-sintered state, and Y4Zr3O 12 While not particularly limited as long as a zirconia calcined body containing the compound (I) can be obtained, it is preferable to maintain the maximum calcination temperature for 30 minutes to 6 hours. Furthermore, the heating rate to the maximum calcination temperature and the temperature decrease rate from the maximum calcination temperature are preferably 300°C / min or less. In a preferred embodiment, the heating rate to the maximum calcination temperature when calcining the zirconia molded body of the present invention 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, and is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. Having a heating rate equal to or greater than the above-mentioned lower limit improves productivity. Furthermore, having a heating rate equal to or less than the above-mentioned upper limit can suppress the volume difference between the interior and exterior of the zirconia molded body or the zirconia calcined body, and, if the zirconia molded body contains an organic substance, can suppress rapid decomposition of the organic substance, thereby suppressing cracking and fracture.

[0089] [Zirconia Sintered Body] Next, the zirconia sintered body will be described. The zirconia sintered body is obtained by firing the zirconia calcined body obtained as described above.

[0090] The content of the stabilizer (yttria and stabilizers other than yttria) in the zirconia sintered body of the present invention is the same as the content of the stabilizer in the zirconia calcined body.

[0091] When the zirconia sintered body of the present invention is compared between a first translucency of a zirconia sintered body produced by firing at 1550°C for 7 minutes at a heating rate of 350°C / min and a second translucency of a zirconia sintered body produced by firing at 1550°C for 120 minutes at a heating rate of 10°C / min, the first translucency is preferably 85% or more of the second translucency, more preferably 86% or more, even more preferably 90% or more, particularly preferably 95% or more, and most preferably substantially the same. Therefore, the zirconia sintered body of the present invention can maintain high translucency equivalent to that of long-term sintering after sintering for a short time at 1550°C for a holding time of 7 minutes or less.

[0092] The zirconia sintered body of the present invention may contain a fluorescent agent. The fluorescent agent is the same as the fluorescent agent in the zirconia calcined body. In this specification, regarding the fluorescent agent, "relative to 100% by mass of zirconia contained in the zirconia calcined body" can be read as "relative to 100% by mass of zirconia contained in the zirconia sintered body."

[0093] The zirconia sintered body of the present invention may contain a colorant. Examples of colorants include those similar to those in the zirconia calcined body. The content of the colorant in the zirconia sintered body is not particularly limited and can be adjusted appropriately depending on the type of colorant and the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the content of the colorant, calculated as the oxide of the metal element contained in the colorant, relative to 100% by mass of zirconia contained in the zirconia sintered body, is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more. Furthermore, the content of the colorant, calculated as the oxide of the metal element contained in the colorant, is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and may even be 0.1% by mass or less, or even 0.05% by mass or less.

[0094] In order to adjust the translucency of the zirconia sintered body of the present invention, the zirconia sintered body of the present invention may contain a translucency adjuster. Examples of the translucency adjuster include the same ones as the translucency adjuster in the zirconia calcined body. The content of the translucency adjuster in the zirconia sintered body is not particularly limited and can be appropriately adjusted depending on the type of translucency adjuster and the application of the zirconia sintered body, but from the viewpoint of being preferably usable as a dental prosthesis, the content is preferably 0.1 mass% or less relative to 100 mass% of zirconia contained in the zirconia sintered body.

[0095] 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. The relative density can be calculated as the ratio of the actual density measured by Archimedes' method to the theoretical density.

[0096] The density of the zirconia sintered body is set to 5.80 g / cm because the higher the density, the fewer internal voids there are and the less light scattering there is, which improves the translucency. 3 It is preferable that the density is 5.82 g / cm or more. 3 More preferably, it is 5.87 g / cm or more. 3 It is more preferable that the zirconia sintered body contains substantially no voids.

[0097] The higher the mechanical strength of the zirconia sintered body, the more preferable. For example, the biaxial bending strength is preferably 800 MPa or more, more preferably 820 MPa or more, and even more preferably 840 MPa or more. The biaxial bending strength can be measured in accordance with ISO 6872:2015.

[0098] [Method for Producing Zirconia Sintered Body] Examples of methods for producing the zirconia sintered body of the present invention include a method for producing a zirconia sintered body by firing the zirconia calcined body described above. A preferred method includes a step of firing the zirconia calcined body described above at a temperature higher than 1200°C and not higher than 1700°C under atmospheric pressure (hereinafter also referred to as the "firing step"). This production method makes it possible to easily produce the zirconia sintered body of the present invention, which has excellent translucency after sintering for a short period of time, i.e., a holding time of 2 minutes at the maximum sintering temperature. Furthermore, the production method of the present invention makes it possible to easily produce the zirconia sintered body of the present invention, which maintains high translucency comparable to that obtained by long-term sintering after sintering for a short period of time, i.e., a holding time of 7 minutes or less at 1550°C.

[0099] When the zirconia calcined body of the present invention is fired to produce a sintered body, the maximum sintering temperature is preferably set under conditions that maximize the translucency of the zirconia sintered body. From the viewpoint of easily obtaining the desired zirconia sintered body under normal pressure, the maximum sintering temperature is preferably above 1200°C, more preferably 1250°C or higher, and even more preferably 1300°C or higher. Furthermore, the maximum sintering temperature is preferably 1700°C or lower, more preferably 1650°C or lower, and even more preferably 1600°C or lower. By setting the maximum sintering temperature at or above the above lower limit and below the above upper limit, sintering can proceed sufficiently, making it easy to obtain a dense sintered body. Furthermore, by setting the maximum sintering temperature below the above upper limit, deactivation of the fluorescent agent can be suppressed. The maximum sintering temperature is not particularly limited as long as it is within the above-mentioned range and is higher than the calcination temperature (maximum calcination temperature) in the calcination step, and may be set to any temperature, such as a temperature 50°C or higher than the maximum calcination temperature, a temperature 100°C or higher than the maximum calcination temperature, a temperature 200°C or higher than the maximum calcination temperature, or a temperature 300°C or higher than the maximum calcination temperature.

[0100] When producing a sintered body, there is no particular limitation on the sintering time as long as the holding time at the maximum sintering temperature is 7 minutes or less, but in order to be able to efficiently and stably obtain the desired zirconia sintered body with good productivity, the holding time at the maximum sintering temperature is preferably 5 minutes or less, more preferably 4 minutes or less, even more preferably 3 minutes or less, and particularly preferably 2 minutes or less. The holding time is preferably 30 seconds or more, more preferably 45 seconds or more, and even more preferably 1 minute or more.

[0101] When a zirconia sintered body is produced using the zirconia calcined body of the present invention, the firing time for producing the sintered body can be shortened without decreasing the translucency of the zirconia sintered body. In particular, the holding time at the maximum sintering temperature for producing the sintered body can be shortened to 7 minutes or less (e.g., 2 minutes). This improves production efficiency, and when the zirconia calcined body of the present invention is used for a dental product, the time required from determining the dimensions of the dental product to be used for treatment and cutting it to making the dental product ready for treatment can be shortened, thereby reducing the time burden on the patient. It also reduces energy costs. Furthermore, by keeping the holding time at the maximum sintering temperature below the above upper limit, deactivation of the fluorescent agent can be suppressed.

[0102] The temperature increase rate and temperature decrease rate in the firing step are preferably set so as to shorten the time required for the firing step. For example, the temperature increase rate can be set so as to reach the maximum sintering temperature in the shortest time depending on the performance of the firing furnace. The temperature increase rate to the maximum sintering temperature can be, for example, 10°C / min or more, 50°C / min or more, 100°C / min or more, 120°C / min or more, 150°C / min or more, 200°C / min or more, 250°C / min or more, 300°C / min or more, or 350°C / min or more. The temperature decrease rate is preferably set so as not to cause defects such as cracks in the sintered body. For example, after heating is completed, the sintered body can be allowed to cool at room temperature.

[0103] The calcination and firing in the present invention can be carried out using a firing furnace. There are no particular limitations on the type of firing furnace, and for example, electric furnaces and degreasing furnaces commonly used in industry can be used. A commercially available dental firing furnace (for example, the trade name "Sintra CS" (manufactured by Shenpaz)) can also be used.

[0104] The zirconia sintered body of the present invention can be produced without HIP treatment, but by optionally performing HIP treatment after sintering under normal pressure, it is possible to further improve translucency and mechanical strength. Hereinafter, the sintered body obtained by sintering at the above-mentioned maximum 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." HIP treatment can be performed using a known hot isostatic pressing (HIP) device.

[0105] When the primary sintered body is subjected to HIP treatment, the HIP pressure is not particularly limited, and since a dense sintered body with high mechanical strength can be obtained, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more. The upper limit of the HIP pressure is not particularly limited, but can be, for example, 400 MPa or less, 300 MPa or less, or even 200 MPa or less.

[0106] When the primary sintered body is subjected to HIP treatment, the temperature rise 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. The temperature rise 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 temperature rise rate at or above the lower limit, productivity is improved.

[0107] When the primary sintered body is subjected to the HIP treatment, the HIP time (the time during which the maximum pressure and temperature are maintained) is not particularly limited, and since a dense zirconia sintered body with high mechanical strength can be obtained, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Moreover, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0108] In the method for producing a zirconia sintered body of the present invention, the pressure medium used in HIPing the primary sintered body is not particularly limited. From the viewpoint of minimizing the effect on zirconia, the pressure medium can be at least one selected from the group consisting of oxygen, oxygen containing 3% hydrogen, air, and an inert gas (e.g., nitrogen, argon, etc.). When the primary sintered body is HIPed in an oxygen-mixed gas atmosphere, the oxygen concentration is not particularly limited, but can be, for example, more than 0% and 20% or less. When an oxygen-mixed gas is used, at least one inert gas (e.g., nitrogen, argon, etc.) can be selected as the gas other than oxygen.

[0109] If the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, black discoloration may occur due to oxygen defects. In this case, to remove the black discoloration, it is preferable to include a heat treatment step (hereinafter also referred to as a "tempering treatment") in the air or in an oxygen-excess atmosphere at 1650°C or less after the HIP treatment. From the viewpoint of efficient heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere. An oxygen-excess atmosphere means that the oxygen concentration is higher than that of the air. The oxygen-excess atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and 100% or less, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%. If the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, black discoloration may occur due to oxygen defects. In this case, to remove the black discoloration, it is preferable to include a heat treatment step (hereinafter also referred to as a "tempering treatment") in the air or in an oxygen-excess atmosphere at 1650°C or less after the HIP treatment. From the viewpoint of efficient heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere. An oxygen-excess atmosphere means that the oxygen concentration is higher than that of the air. The oxygen-excess atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and not more than 100%, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%.

[0110] The zirconia sintered body of the present invention is not particularly limited as long as it exhibits the effects of the present invention, and may be a primary sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment.

[0111] The temperature of the heat treatment in the air or in an oxygen-excess atmosphere can be appropriately changed depending on the aesthetics of the zirconia sintered body (e.g., the shade of a dental prosthesis). In a preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1650°C or less, more preferably 1600°C or less, and even more preferably 1550°C or less, from the viewpoint of the aesthetics of the zirconia sintered body. In another preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1400°C or less, more preferably 1300°C or less, and even more preferably 1200°C or less, from the viewpoint of the aesthetics of the zirconia sintered body. Furthermore, in any embodiment, the temperature of the heat treatment is preferably 500°C or more, more preferably 600°C or more, and even more preferably 700°C or more.

[0112] A general dental zirconia firing furnace can be used for the tempering treatment. Commercially available dental zirconia firing furnaces may be used. Examples of commercially available dental zirconia firing furnaces include Noritake Katana (registered trademark) F-1, F-1N, F-2, and F-2N (all manufactured by SK Medical Electronics Co., Ltd.).

[0113] The zirconia sintered body obtained by firing the zirconia calcined body of the present invention can be suitably used for dental products. Examples of dental products include copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, orthodontic wires, and laminate veneers. By using the zirconia calcined body of the present invention for parts such as implant screws and implant fixtures, discoloration of the gums caused by metal materials can be suppressed, resulting in excellent aesthetics. Furthermore, while an appropriate method for manufacturing these products can be selected depending on the application, for example, dental products can be obtained by cutting the zirconia calcined body of the present invention and then firing it. It is preferable to use a CAD / CAM system for the cutting process. The CAD / CAM system is not particularly limited, and known devices can be used. Examples of known devices include a CAD / CAM system ("Katana (registered trademark) CAD / CAM System," manufactured by Kuraray Noritake Dental Co., Ltd.).

[0114] An example of a preferred embodiment (X-1) is a zirconia sintered body containing zirconia and a stabilizer capable of suppressing a phase transition of zirconia, wherein at least one zirconia crystal grain contained in the zirconia sintered body has a portion having a concentration gradient in which the concentration (content) of the stabilizer in the same crystal grain decreases from the center side of the crystal grain toward the outer crystal grain boundary.

[0115] The zirconia sintered body according to the present embodiment (X-1) is sufficient if at least one zirconia crystal particle has a portion having the concentration gradient, and may include a portion where the increase / decrease trend of the stabilizer content changes due to unevenness in the stabilizer content (uneven concentration), etc. The stabilizer in the zirconia sintered body according to the present embodiment (X-1) can be the same as yttria and stabilizers other than yttria that can suppress the phase transition of zirconia, which can be used in the zirconia calcined body according to the present invention. For the zirconia sintered body according to the present embodiment (X-1), the stabilizer that can suppress the phase transition of zirconia is preferably yttria, as this stabilizer has better translucency.

[0116] The zirconia sintered body according to this embodiment (X-1) is preferably a zirconia sintered body in which the concentration gradient is 0.1 to 3 mol% relative to the total moles of zirconia and stabilizer. From the viewpoint of excellent translucency, the concentration gradient (the difference in content between the center 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 translucency, the 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. The method for evaluating the concentration gradient is as described in the Examples below.

[0117] Hereinafter, the zirconia sintered body according to this embodiment (X-1) will be described as a suitable example in which the stabilizer capable of suppressing the phase transition of zirconia is yttria. The zirconia sintered body according to this embodiment (X-1) has a crystal system of Y4Zr3O 12The zirconia sintered body exhibits excellent translucency even when the holding time at the maximum sintering temperature is 2 minutes when firing the zirconia calcined body containing the above-mentioned yttria. When observed using a transmission electron microscope (TEM), the zirconia sintered body having the above-described properties has a portion with a concentration gradient in which the yttria content decreases in the direction indicated by the arrow, i.e., from the center (e.g., center portion 1) toward the outer grain boundary, as shown in FIG. 2. The center can be any central portion inside the same crystal grain, and may be, for example, the center of gravity (geometric center). The center of gravity can be determined using known analysis software (e.g., image analysis software (trade name "Image-Pro Plus" manufactured by Hakuto Co., Ltd.)). The center of gravity can be determined from the outline of the crystal grain. It is known from the prior art that, when observed using a transmission electron microscope (TEM) during the final stage of sintering, the yttria concentration in the same crystal grain has a concentration gradient in which the yttria concentration decreases from the outer grain boundary toward the center of the crystal grain. Therefore, the zirconia sintered body according to this embodiment (X-1) has a tendency completely opposite to that of the conventional technology.

[0118] The method for producing the zirconia sintered body according to the present embodiment (X-1) is not particularly limited as long as it has the crystal grain structure of the zirconia sintered body described above. The zirconia sintered body according to the present embodiment (X-1) is preferably produced by subjecting a zirconia sintered body containing both zirconia and yttria to a pulverization treatment with excessive energy compared to conventional sintered bodies, and has a crystal system of Y4Zr3O 12A zirconia calcined body containing the compound (I) is obtained, and by further firing the zirconia calcined body, it is possible to produce the zirconia sintered body by short-time firing (for example, a holding time of 2 minutes at the maximum sintering temperature). It is also believed that in the zirconia sintered body according to the present embodiment (X-1), by short-time firing (for example, a holding time of 2 minutes at the maximum sintering temperature), at least one of the zirconia crystal particles has an yttria concentration gradient. Furthermore, in the zirconia sintered body according to the present embodiment (X-1), even in a cubic crystal, which is usually considered to have high translucency but low mechanical strength, the yttria concentration gradient allows for the presence of low-yttria regions at the periphery (grain boundaries) of the zirconia crystal particles, which have a toughening mechanism (stress-induced phase transformation). It is therefore believed that the zirconia sintered body obtained by short-time firing (for example, a holding time of 2 minutes at the maximum sintering temperature) can achieve both excellent mechanical strength and translucency. The yttria content of the zirconia crystal particles can be measured, for example, by scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS).

[0119] A more preferred embodiment (X-1-1) is a zirconia calcined body containing zirconia and yttria as components, and having a crystal system of Y4Zr3O 12 and a stabilizer capable of suppressing a phase transition of zirconia, the stabilizer being obtained by firing a zirconia calcined body, the stabilizer comprising: zirconia; and a zirconia sintered body comprising: zirconia; and a stabilizer capable of suppressing a phase transition of zirconia, wherein at least one zirconia crystal grain contained in the zirconia sintered body has a portion having a concentration gradient in which the concentration of the stabilizer in the same crystal grain decreases from the center side of the crystal grain toward the outer crystal grain boundary.

[0120] Another preferred embodiment (X-2) is a zirconia sintered body containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, the zirconia sintered body comprising: zirconia crystal particles (L) having a stabilizer content of 4 to 6 mol % relative to the total moles of zirconia and the stabilizer; and zirconia crystal particles (S) having a stabilizer content of 1 to 3 mol % relative to the total moles of zirconia and the stabilizer. In TEM observation, the number of zirconia crystal particles (L) observed within a 5 μm x 5 μm area is preferably 3 or more, more preferably 5 or more, even more 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 x 5 μm area is preferably 5 or more, more preferably 10 or more, even more preferably 15 or more, and particularly preferably 20 or more.

[0121] The zirconia sintered body according to the present embodiment (X-2) is not particularly limited, and may contain zirconia crystal particles whose content of the stabilizer is more than 3 mol % and less than 4 mol % with respect to the total moles of zirconia and the stabilizer.

[0122] The stabilizer in the zirconia sintered body according to the present embodiment (X-2) can be the same as yttria and stabilizers other than yttria that can suppress the phase transition of zirconia and can be used in the zirconia calcined body according to the present invention. For the zirconia sintered body according to the present embodiment (X-2), the stabilizer that can suppress the phase transition of zirconia is preferably yttria, since this stabilizer has better translucency.

[0123] The zirconia sintered body according to this embodiment (X-2) is preferably a zirconia sintered body in which the average crystal particle size of the zirconia crystalline particles (L) is within the range of 0.5 to 2.0 μm, and the average crystal particle size of the zirconia crystalline particles (S) is within the range of 0.1 to 0.3 μm, from the viewpoint of more excellent translucency and mechanical strength. In the zirconia sintered body according to this embodiment (X-2), the average crystal particle size of the zirconia crystalline 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, from the viewpoint of more excellent translucency and mechanical strength. Furthermore, the average crystal particle size of the zirconia crystalline 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, from the viewpoint of more excellent translucency and mechanical strength.

[0124] In the zirconia sintered body according to this embodiment (X-2), the average crystal particle size of the zirconia crystalline 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, from the viewpoint of more excellent translucency and mechanical strength. Furthermore, the average crystal particle size of the zirconia crystalline 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, from the viewpoint of more excellent translucency and mechanical strength. The average crystal particle sizes of the zirconia crystalline particles (L) and the zirconia crystalline particles (S) are measured by the method described in the Examples below.

[0125] Hereinafter, the zirconia sintered body according to this embodiment (X-2) will be described as a suitable example in which the stabilizer capable of suppressing the phase transition of zirconia is yttria.

[0126] The method for producing the zirconia sintered body according to the present embodiment (X-2) is not particularly limited as long as it has the crystal grain structure of the zirconia sintered body described above. The zirconia sintered body according to the present embodiment (X-2) is preferably produced by subjecting a zirconia sintered body containing both zirconia and yttria to a pulverization treatment with excessive energy compared to conventional sintered bodies, and has a crystal system of Y4Zr3O 12 A zirconia calcined body containing the zirconia crystal particles (L) and the zirconia crystal particles (S) is obtained, and by further firing the zirconia calcined body, it is possible to produce the zirconia sintered body by short-time firing (for example, a holding time of 2 minutes at the maximum sintering temperature). It is also believed that the zirconia sintered body according to the present embodiment (X-2) becomes a zirconia sintered body containing the zirconia crystal particles (L) and the zirconia crystal particles (S) by short-time firing (for example, a holding time of 2 minutes at the maximum sintering temperature). Furthermore, the zirconia sintered body according to the present embodiment (X-2) contains the zirconia crystal particles (L) and the zirconia crystal particles (S) having the above-described stabilizer content (preferably the yttria content) and average crystal particle sizes, thereby ensuring mechanical strength through fine crystal particles and reducing interference of light with wavelengths in the visible light region. It is also believed that the zirconia sintered body obtained by short-time firing (for example, a holding time of 2 minutes at the maximum sintering temperature) can achieve both excellent mechanical strength and translucency.

[0127] The zirconia sintered body according to this embodiment (X-2) has a crystal system of Y4Zr3O 12 The zirconia sintered body according to the present embodiment (X-2) has a high yttria content region where 4 to 6 mol % of zirconia crystal particles (L) are present and a low yttria content region where 1 to 3 mol % of zirconia crystal particles (S) are present, and is therefore considered to have a crystalline structure that combines tetragonal crystals with high strength and cubic crystals with high transparency, thereby achieving both excellent strength and translucency as a sintered body.

[0128] A more preferred embodiment (X-2-1) is a zirconia calcined body containing zirconia and yttria as components, and having a crystal system of Y4Zr3O 12 and a zirconia sintered body obtained by firing a zirconia calcined body, the zirconia sintered body containing zirconia and a stabilizer capable of suppressing a phase transition of zirconia, the zirconia sintered body containing: zirconia crystal particles (L) in which the concentration of the stabilizer is 4 to 6 mol % relative to the total moles of zirconia and the stabilizer; and zirconia crystal particles (S) in which the concentration of the stabilizer is 1 to 3 mol % relative to the total moles of zirconia and the stabilizer.

[0129] The zirconia sintered body according to this embodiment (X-2) is more preferably a zirconia sintered body comprising: zirconia crystal particles (Lx) in which the concentration of the stabilizer is 5 to 6 mol % relative to the total moles of zirconia and the stabilizer; and zirconia crystal particles (Sx) in which the concentration of the stabilizer is 1 to 2 mol % relative to the total moles of zirconia and the stabilizer. Furthermore, from the viewpoint of more excellent translucency and mechanical strength, the zirconia sintered body comprising zirconia crystal particles (Lx) and zirconia crystal particles (Sx) is more preferably a zirconia sintered body in which the average crystal particle size of the zirconia crystal particles (Lx) is within the range of the average crystal particle size of the zirconia crystal particles (L), and the average crystal particle size of the zirconia crystal particles (S) is within the above-mentioned range of the average crystal particle size of the zirconia crystal particles (S).

[0130] Another preferred embodiment (X-3) is a zirconia sintered body containing zirconia and a stabilizer capable of suppressing a phase transition of zirconia, wherein at least one zirconia crystal particle contained in the zirconia sintered body has a portion having a concentration gradient in which the concentration of the stabilizer in the same crystal particle decreases from the center of the crystal grain toward the outer grain boundary, and the zirconia crystal particles are zirconia crystal particles (L) having a stabilizer content of 4 to 6 mol % relative to the total moles of zirconia and the stabilizer, and further include zirconia crystal particles (S) having a stabilizer content of 1 to 3 mol % relative to the total moles of zirconia and the stabilizer.

[0131] The concentration gradient possessed by the zirconia crystal particles in the zirconia sintered body according to the present embodiment (X-3) is as explained in the above-mentioned embodiment (X-1). The zirconia crystal particles (L) and zirconia crystal particles (S) in the zirconia sintered body according to the present embodiment (X-3) are as explained in the above-mentioned embodiment (X-2). In the present embodiment (X-3), the zirconia crystal particles having a portion having the concentration gradient are zirconia crystal particles (L) because of their superior translucency and mechanical strength.

[0132] In the zirconia sintered body according to this embodiment (X-3), when 10 zirconia crystal particles (L) are arbitrarily selected from a TEM image (one visual field) obtained by TEM observation of the zirconia sintered body, preferably 5 or more, more preferably 6 or more, and even more preferably 7 or more of the zirconia crystal particles (L) have the above-described concentration gradient. If 10 zirconia crystal particles (L) cannot be obtained from one visual field, the number of visual fields may be increased to select a total of 10 zirconia crystal particles (L). Similarly, in this specification, when selecting a specific number of crystal particles (e.g., 10 or 20) in one visual field, if the desired number of particles cannot be confirmed in one visual field, the number of visual fields may be increased to 2 or more, and the desired total number (e.g., 10 or 20) may be selected.

[0133] A more preferred embodiment (X-3-1) is a zirconia calcined body containing zirconia and yttria as components, and having a crystal system of Y4Zr3O 12 and a zirconia sintered body containing zirconia and yttria, the zirconia sintered body being obtained by firing a zirconia calcined body comprising the above-mentioned. At least one zirconia crystal particle contained in the zirconia sintered body has a portion having a concentration gradient in which the concentration (content) of the yttria in the same crystal particle decreases from the center side of the crystal grain toward the outer crystal grain boundary, the zirconia crystal particles being zirconia crystal particles (L) having an yttria content of 4 to 6 mol % relative to the total moles of zirconia and yttria, and further including zirconia crystal particles (S) having an yttria content of 1 to 3 mol % relative to the total moles of zirconia and yttria.

[0134]

[0023] Another more preferred embodiment (X-3-2) is a zirconia sintered body comprising: zirconia crystal particles (Lx) having a stabilizer concentration of 5 to 6 mol % relative to the total moles of zirconia and the stabilizer; and zirconia crystal particles (Sx) having a stabilizer concentration of 1 to 2 mol % relative to the total moles of zirconia and the stabilizer, wherein the zirconia crystal particles having a portion having a stabilizer concentration gradient are the zirconia crystal particles (Lx). Another more preferred embodiment (X-3-3) is a zirconia sintered body comprising zirconia crystal particles (Lx) and zirconia crystal particles (Sx), wherein the average crystal particle size of the zirconia crystal particles (Lx) is within the average crystal particle size range of the zirconia crystal particles (L), and the average crystal particle size of the zirconia crystal particles (S) is within the above-mentioned average crystal particle size range of the zirconia crystal particles (S), from the viewpoint of superior translucency and mechanical strength. Furthermore, the zirconia sintered body according to the present embodiment (X-3) is not particularly limited, and may contain zirconia crystal particles whose content of the stabilizer is more than 3 mol % and less than 4 mol % with respect to the total moles of zirconia and the stabilizer.

[0135] The present invention includes embodiments in which all or part of the above-described configurations are combined in various ways within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved. For example, in the preferred embodiments (X-1) to (X-3), all or part of the configurations can be combined in various ways within the scope of the description in this specification. Specifically, the present invention also includes embodiments in which the biaxial bending strength of the zirconia sintered body according to the preferred embodiments (X-1) to (X-3) is 800 MPa or more.

[0136] Next, the present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way, and many modifications within the technical scope of the present invention are possible by those skilled in the art.

[0137] [Example 1] Commercially available zirconia powder (YO: 0 mol%) and commercially available yttria powder were added to water, and then placed in a ball mill along with zirconia grinding media (diameter: 2 mm). The mixture was milled for 144 hours in a ball mill to obtain a slurry (average particle size: 0.2 μm or less).

[0138] Next, an organic binder was added to the obtained slurry, and the mixture was mixed and stirred. The stirred slurry was dried and granulated using a spray dryer to obtain a powder. This powder was poured into a cylindrical mold and uniaxially pressed at a pressure of 200 MPa to obtain a compact. The obtained compact was placed in an electric furnace, heated from room temperature at a rate of 10°C / min, and held at 500°C for 2 hours to degrease the organic components. Thereafter, the temperature was raised at a rate of 10°C / min and held at 955°C (maximum calcination temperature) for 2 hours, and then slowly cooled at a rate of -10°C / min to obtain a zirconia calcined body.

[0139] Examples 2 to 11 and Comparative Examples 1 to 4 Zirconia calcined bodies were produced in the same manner as in Example 1, except for the conditions as shown in Table 1. In Examples 2 to 11 and Comparative Examples 1 to 4, the same yttria raw material as in Example 1 was used. In Example 4, instead of using a ball mill, grinding was performed using a bead mill with zirconia grinding media having a diameter of 0.1 mm, and the grinding time was changed to the time shown in Table 1. In Example 11, grinding was performed using the same ball mill as in Example 1, followed by grinding using a bead mill with zirconia grinding media having a diameter of 0.1 mm, and the grinding time for each grinding was changed to the time shown in Table 1. In Table 1, 1.5Y zirconia (YO: 1.5 mol%) was produced as follows. Commercially available zirconia powder (YO: 0 mol%) and commercially available yttria powder were added to water such that the yttria content was 1.5 mol% relative to the total mol% of zirconia and yttria. These and zirconia grinding media (diameter: 2 mm) were placed in a ball mill container and milled in a ball mill for 48 hours to obtain a slurry (average particle size: 0.2 μm or less). The resulting slurry was then dried and granulated using a spray dryer to obtain a powder. The resulting powder was then heated and held at 1000°C for 100 hours to obtain a raw material. In Table 1, 40Y zirconia (YO: 40 mol%) was produced as follows. Commercially available zirconia powder (YO: 0 mol%) and commercially available yttria powder were added to water such that the yttria content was 40 mol% relative to the total mol% of zirconia and yttria. These materials and zirconia grinding media (diameter: 2 mm) were placed in a ball mill container and ground for 48 hours in a ball mill to obtain a slurry (average particle size: 0.2 μm or less). The resulting slurry was then dried and granulated in a spray dryer to obtain a powder. The resulting powder was then heated and held at 1000° C. for 100 hours to obtain a raw material.

[0140]

[0141] <Y4Zr3O in zirconia calcined body> 12Evaluation of the presence or absence of Y4Zr3O in the zirconia calcined bodies obtained in each Example and Comparative Example 12 The presence or absence of was evaluated using a TEM. Specifically, the calcined body was polished to a thickness of 30 μm, and the surface of the calcined body was processed using a precision ion polishing system (trade name "Model 691 PIPS", manufactured by Gatan Corporation (USA)). Using the prepared sample, an electron beam diffraction image was obtained using an atomic resolution analytical electron microscope (trade name "JEM-ARM200F ACCELARM", manufactured by JEOL Ltd.) with a camera length of 1.0 cm and an acceleration voltage of 200 kV. First, from the obtained diffraction image, the distances d1 and d2 (corresponding to the interplanar spacing) and their angles (corresponding to the interplanar angle φ) of the diffraction spots were measured as shown in FIG. 1. Next, Y4Zr3O 12 Using the formulas (1-3) and (1-4) for calculating the hexagonal crystal plane spacing and interplanar angle, into which the lattice constants (a=9.738Å, c=9.115Å) of Y4Zr3O are substituted, it was confirmed whether there was a combination of plane indices (h1, k1, l1) (h2, k2, l2) that corresponded to the measured plane spacing (d1, d2) and interplanar angle (φ). 12 The lattice constant of M4Zr3O is described 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. 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 ) l1 l2) / ((h1 2 +k1 2 + h1 k1 + (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, the zirconia calcined bodies of Examples 1 to 11 were found to have a Y4Zr3O 12 On the other hand, in the zirconia calcined bodies of Comparative Examples 1 to 4, Y4Zr3O 12 The existence of could not be confirmed.

[0142] <Evaluation of the proportion of crystal systems in zirconia calcined bodies> The Y4Zr3O of the zirconia calcined bodies obtained in each example and comparative example 12 The probability of occurrence f d , tetragonal crystallinity f t , cubic crystal fraction f c , and the monoclinic fraction f m was determined by analyzing the crystal system in the zirconia calcined body. Specifically, for X-ray diffraction, a fully automatic horizontal multipurpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and X-ray analysis integrated software (SmartLab Studio II, manufactured by Rigaku Corporation) were used to measure under the following conditions, and the area intensity of each peak (peak area intensity I) was determined. X-ray source: Cu Kα (λ = 1.54186 Å) Goniometer length: 300 mm Optical system: focusing method Detector: high-speed one-dimensional X-ray detector (D / teX Ultra 250) Monochromatization: Kβ filter Tube voltage: 40 kV Tube current: 30 mA Scan axis: 2θ / θ Scan speed: 0.2 ° / min Sampling step: 0.01 °

[0143] Using the area intensity of each peak, Y4Zr3O 12 The probability of occurrence f d (%), and monoclinic crystal ratio f m The results are shown in Table 2. 12 The probability of occurrence f d In calculating (%), Y4Zr3O 12Since the positions of the main peaks of the tetragonal and cubic crystals are similar, when it was confirmed that these crystal systems coexisted, peak separation was performed. Specifically, first, the presence or absence of each crystal system was confirmed. 12 The presence or absence of the tetragonal crystal system was confirmed by the sub-peaks around 34.6° and 35.4°. The presence or absence of the cubic crystal system was confirmed by the sub-peak around 35.0°. Next, peak separation was performed based on the confirmed crystal system. For example, when all three crystal systems were confirmed, the peak where the three crystal systems overlap, seen around 30°, was separated into Y4Zr3O with a peak top at 29.6°. 12 The peaks of the three crystal systems, i.e., the tetragonal system having a peak top at 30.3°, and the cubic system having a peak top at 30.0°, are separated by adjusting the half width and peak intensity at the peak top position so that each peak is approximated by a Gaussian function. d , I t , I c When the presence of two types of crystal systems was confirmed, the peaks of the two crystal systems were separated and the area intensity of each was calculated.

[0144] <Evaluation of Crystal Grains in Zirconia Sintered Body> Zirconia crystal grains in a zirconia sintered body were identified using the following procedure, and then the yttria content of the zirconia crystal grains, the average crystal grain size of the zirconia crystal grains (L) and the zirconia crystal grains (S), and the concentration gradient of yttria in the zirconia crystal grains were measured. <Method for Identifying Zirconia Crystal Grains> Zirconia crystal grains (zirconia concentration of 80% by mass or more) were identified using the following method. When measured in a bright field (20,000x magnification) in TEM observation, particles with approximately constant brightness, which included an observation point (observation area of ​​5 × 5 nm) where the zirconia concentration was 80% by mass or more using scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS), were visually determined to be a single zirconia crystal grain. <Yttria Content of Zirconia Crystal Particles> The yttria content of the zirconia crystal particles identified as described above was measured by STEM-EDS. Here, the observation area was square, and the observation area was set so that at least three vertices of the square were inscribed in the grain boundary of the crystal particle, forming the largest square shape possible within the crystal particle. In the zirconia sintered body of Example 1 obtained by firing using the method described in <Evaluation of Translucency of Zirconia Sintered Body (Measurement of ΔL*(W-B) 1)> (short-term firing at 1580°C for 2 minutes), there were 100 or more zirconia crystal particles with an yttria content of 4 to 6 mol% and 100 or more zirconia crystal particles with an yttria content of 1 to 3 mol% (total for 10 fields of view). Furthermore, there were 100 or more zirconia crystal particles each having an yttria content in the range of 5 to 6 mol% and 100 or more zirconia crystal particles having an yttria content in the range of 1 to 2 mol (total for 10 visual fields). On the other hand, in the zirconia sintered body of Comparative Example 3, only zirconia crystal particles having an yttria content in the range of 4 to 6 mol% were present, and no zirconia crystal particles having an yttria content in the range of 1 to 3 mol were confirmed.<Method for measuring the average crystal particle size of zirconia crystal particles (L) and zirconia crystal particles (S)> Next, zirconia crystal particles having an yttria content in the range of 4 to 6 mol% were designated as zirconia crystal particles (L), and zirconia crystal particles having an yttria content in the range of 1 to 3 mol% were designated as zirconia crystal particles (S). The circle-equivalent diameter (area-equivalent circle diameter) of each crystal particle identified by the above-described method for identifying zirconia crystal particles using TEM observation was designated as the crystal particle size of each crystal particle, and the arithmetic mean of the circle-equivalent diameters of 100 randomly selected crystal particles was designated as the average crystal particle size of the zirconia crystal particles. More specifically, the arithmetic mean of the circle-equivalent diameters of 10 randomly selected crystal particles in one visual field was calculated for the 10 visual fields, and this was designated as the average crystal particle size of the zirconia crystal particles. In the zirconia sintered body of Example 1, the average crystal particle size of the zirconia crystal particles (L) was 1.0 μm, and the average crystal particle size of the zirconia crystal particles (S) was 0.2 μm. Furthermore, zirconia crystal particles having an yttria content in the range of 5 to 6 mol% can be designated as zirconia crystal particles (Lx), and zirconia crystal particles having an yttria 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 crystal particle size of the zirconia crystal particles (Lx) was 1.2 μm, and the average crystal particle size of the zirconia crystal particles (Sx) was 0.2 μm. <Measurement of the concentration gradient of yttria in zirconia crystal particles> The yttria content in the central portion and at the grain boundaries of the zirconia crystal particles identified as described above using TEM observation was measured using STEM-EDS (observation area 5 × 5 nm). The yttria content in the central portion was measured at the center of gravity of the crystal grain, and the yttria content in the grain boundary was measured in a region 1 / 10 of the distance from the grain boundary to the center of gravity on the grain boundary side. When an arbitrary zirconia crystal grain (L) was selected and measured in the zirconia sintered body of Example 1, the yttria content in the zirconia crystal grain was 5.9 mol % at the center (center of gravity) and 4.2 mol % at the grain boundary.Furthermore, when 10 randomly selected zirconia crystal particles (L) were measured from multiple fields of view, 9 zirconia crystal particles were confirmed in which the yttria content at the grain boundaries was 0.15 mol% or more lower than that at the center (center of gravity). On the other hand, in the zirconia sintered body of Comparative Example 3, the yttria content at the center (center of gravity) and the grain boundaries of the zirconia crystal particles was the same, or the yttria content at the grain boundaries was higher than that at the center (center of gravity). The center of gravity of the crystal particles was determined from the outline of the crystal particles using image analysis software (trade name "Image-Pro Plus", manufactured by Hakuto Co., Ltd.).

[0145] <Evaluation of Translucency of Zirconia Sintered Body (Measurement 1 of ΔL*(W−B))> The zirconia calcined bodies obtained in each of the Examples and Comparative Examples were subjected to short-term firing in a dental firing furnace (trade name "Sintra CS" (manufactured by Shenpaz)) at a heating rate of 350°C / min at 1580°C for 2 minutes. Each of the obtained zirconia sintered bodies was polished into a flat plate sample with a thickness of 1.0 mm, which was used as a sample for measuring translucency. The translucency of the sample was measured using a spectrophotometer (trade name "Crystal Eye") manufactured by Olympus Corporation, using a 7-band LED light source in measurement mode. As in <Measurement 2 of Evaluation of Translucency of Zirconia Sintered Body (ΔL*(W-B))> below, the lightness (LW*) when chromaticity was measured against a white background and the lightness (LB*) when chromaticity was measured against a black background for the same sample using the same measuring device, measuring mode, and light source were measured, and the difference between the two (ΔL*=(LW*)-(LB*)) was defined as the translucency (ΔL*(W-B)) (arithmetic mean value of n=3). A translucency ΔL*(W-B) of 13 or more was considered acceptable. The results are shown in Table 2 below.

[0146] <Measurement 2 of Translucency of Zirconia Sintered Body (ΔL*(W-B))> The calcined bodies obtained in the Examples and Comparative Examples were fired at a maximum sintering temperature of 1550°C, a heating rate of 350°C / min, and a holding time at the maximum sintering temperature of 7 minutes (7-minute firing), to produce a zirconia sintered body (first sintered body). Next, the calcined bodies produced in the same manner were fired at a maximum sintering temperature of 1550°C, a heating rate of 10°C / min, and a holding time at the maximum sintering temperature of 120 minutes (120-minute firing), to produce a zirconia sintered body (second sintered body). The temperature drop rate was set to 200°C / min for the 7-minute firing and 10°C / min for the 120-minute firing. The two types of zirconia sintered bodies obtained were each polished into a flat plate sample with a thickness of 1.0 mm, which was used as a sample for measuring translucency. The translucency of the sample was measured using a spectrophotometer (product name "Crystal Eye") manufactured by Olympus Corporation, with a measurement mode of 7-band LED light source. Specifically, the translucency of the zirconia sintered body, which was a flat sample, was measured by measuring the lightness (LW*) when the chromaticity was measured against a white background, and by measuring the lightness (LB*) when the chromaticity was measured against a black background using the same measurement device, measurement mode, and light source. The difference between the two (ΔL* = (LW*) - (LB*)) was defined as the translucency (ΔL*(W-B)) (arithmetic mean value of n = 3). The L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013). The first translucency ΔL1*(W-B) of the first sintered body produced by firing at 1550°C for 7 minutes and the second translucency ΔL2*(W-B) of the second sintered body produced by firing at 1550°C for 120 minutes were determined, and the ratio of ΔL1*(W-B) to ΔL2*(W-B) (ΔL1*(W-B) / ΔL2*(W-B)) was calculated as the rate of change in translucency. A rate of change in translucency of 0.85 or more (85% or more) was considered acceptable. The results are shown in Table 2 below.

[0147] <Evaluation of Strength of Zirconia Sintered Body> The zirconia sintered body of Example 1 obtained by firing by the method described in <Evaluation of Translucency of Zirconia Sintered Body (Measurement of ΔL*(W-B) 1)> above (short-term firing with retention at 1580°C for 2 minutes) was used as a 1.0 mm thick plate sample after polishing, and the biaxial bending strength was measured in accordance with ISO 6872:2015 using a universal testing machine "AGS-X" (manufactured by Shimadzu Corporation) with a crosshead speed set to 1.0 mm / min (n=5). The arithmetic mean value was calculated to be 911 MPa. In contrast, the biaxial bending strength was measured and calculated using the commercially available product of Comparative Example 3 in the same manner as in Example 1, and was found to be 600 MPa.

[0148]

[0149] From the above results, it was confirmed that the zirconia calcined body of the present invention has excellent translucency even when the holding time at the maximum sintering temperature is 2 minutes. Furthermore, by using the zirconia calcined body of the present invention, the maximum sintering temperature can be set to less than 1600°C. For example, when the maximum sintering temperature is set to 1550°C, a zirconia sintered body that can maintain high translucency equivalent to that obtained with long-term sintering was obtained after sintering for a short time, i.e., a holding time at 1550°C of 7 minutes or less. In the comparative example, a holding time at the maximum sintering temperature of 2 minutes did not progress sintering sufficiently to achieve the desired translucency. Furthermore, it was confirmed that the zirconia sintered body with excellent translucency obtained using a production method in which the holding time at the maximum sintering temperature when firing the calcined body is 2 minutes has zirconia crystal grains with characteristics different from those of crystal grains observed in sintered bodies of the prior art.

[0150] The zirconia calcined body of the present invention is useful for producing dental products for treatment in dental clinics.

Claims

1. Zirconia, yttria, and Y4Zr3O as the crystal system 12 A zirconia calcined body comprising:

2. Y4Zr3O calculated by the following formula (1-1) 12 The occurrence rate f d The zirconia calcined body according to claim 1, wherein (%) is 2.5% or more. d (%) = I d / (I m +I t +I c +I y +I d )×100 (1-1) (where f d Y4Zr3O 12 In the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the top of the main monoclinic peak appears, and I t represents the integrated intensity of the peak at 2θ = 30.3° where the top of the main peak of the tetragonal system appears, and I c represents the integrated intensity of the peak at 2θ=30.0° where the top of the main peak of the cubic crystal system appears, and I d Y4Zr3O 12 It represents the area intensity of the peak at 2θ=29.6° where the peak top of the main peak of y represents the integrated intensity of the peak near 2θ=29.2° where the top of the main peak of undissolved yttria appears. 12 Since the positions of the main peaks of the tetragonal and cubic crystal systems are similar, the intensity area of ​​each main peak is calculated by peak separation.) 3. The zirconia contains monoclinic zirconia, and the monoclinic ratio f calculated by the following formula (1-2) is m 3. The zirconia calcined body according to claim 1 or 2, wherein f (%) is less than 55%. m (%) = I m / (I m +I t +I c +I y +I d )×100 (1-2) (where f m represents the monoclinic rate (%), and in the XRD measurement, I m represents the integrated intensity of the peak at 2θ=28.2° where the top of the main monoclinic peak appears, and I t represents the integrated intensity of the peak at 2θ = 30.3° where the top of the main peak of the tetragonal system appears, and I c represents the integrated intensity of the peak at 2θ=30.0° where the top of the main peak of the cubic crystal system appears, and I d Y4Zr3O 12 It represents the area intensity of the peak at 2θ=29.6° where the peak top of the main peak of y represents the integrated intensity of the peak near 2θ=29.2° where the top of the main peak of undissolved yttria appears. 12 Since the positions of the main peaks of the tetragonal and cubic crystal systems are similar, the intensity area of ​​each main peak is calculated by peak separation.) 4. The zirconia calcined body according to claim 1 or 2, wherein the content of yttria is 2.5 mol % or more and 10 mol % or less based on the total moles of zirconia and yttria.

5. A zirconia calcined body comprising zirconia and yttria, wherein a first translucency of a first sintered body produced by firing the zirconia calcined body at 1550°C for 7 minutes at a heating rate of 350°C / min is compared with a second translucency of a second sintered body produced by firing the zirconia calcined body at 1550°C for 120 minutes at a heating rate of 10°C / min, and the first translucency is 85% or more of the second translucency.

6. A method for producing a zirconia calcined body according to claim 1 or 2, comprising: a step of producing a zirconia composition containing zirconia particles and yttria particles; a grinding step of grinding the zirconia composition; a shaping step of molding the zirconia composition after the grinding treatment to obtain a molded body; and a calcining step of calcining the molded body, wherein the grinding step (i) uses grinding media having a diameter of less than 1 mm and the grinding time is 10 minutes or more, or (ii) uses grinding media with a diameter of 1 mm or more and the grinding time is more than 40 hours.

7. The method for producing a zirconia calcined body according to claim 6, wherein the calcination temperature in the calcination step is 600 to 1,300°C.

8. A zirconia sintered body comprising zirconia and a stabilizer capable of suppressing a phase transition of zirconia, wherein at least one zirconia crystal grain contained in the zirconia sintered body has a portion having a concentration gradient in which the concentration of the stabilizer in the same crystal grain decreases from the center side of the crystal grain toward the outer crystal grain boundary.

9. The zirconia sintered body according to claim 8, wherein the concentration gradient is 0.1 to 3 mol % based on the total moles of zirconia and stabilizer.

10. The zirconia sintered body according to claim 8 or 9, wherein the stabilizer capable of suppressing the phase transition of zirconia is yttria.

11. A zirconia sintered body comprising zirconia and a stabilizer capable of suppressing a phase transition of zirconia, the zirconia sintered body comprising: zirconia crystal particles (L) having a stabilizer content of 4 to 6 mol % based on the total moles of zirconia and the stabilizer; and zirconia crystal particles (S) having a stabilizer content of 1 to 3 mol % based on the total moles of zirconia and the stabilizer.

12. The zirconia sintered body according to claim 11, wherein the average crystal grain size of the zirconia crystal grains (L) is within the range of 0.5 to 2.0 μm, and the average crystal grain size of the zirconia crystal grains (S) is within the range of 0.1 to 0.3 μm.

13. The zirconia sintered body according to claim 11 or 12, wherein the stabilizer capable of suppressing the phase transition of zirconia is yttria.

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