Zirconia pre-sintered body

Abstract

The present invention provides a green body for obtaining a zirconia sintered body capable of achieving both high strength and high translucency and a method for manufacturing the same. The present invention relates to a zirconia green body, which comprises secondary aggregates having an average particle size of 275 nm or less. The secondary aggregates comprise zirconia and a stabilizer capable of suppressing the phase transition of zirconia. Further, the secondary aggregates comprise large particles having an average primary particle size of 100 nm or more and 200 nm or less and small particles having an average primary particle size of 10 nm or more and less than 60 nm.

Description

Technical Field

[0001] The present invention relates to a green compact for obtaining a sintered body of zirconia (zirconium(IV) oxide; ZrO₂) having both high strength and high translucency, and a method for manufacturing the same. Background Art

[0002] Sintering of ceramics generally refers to a phenomenon of mass transfer in the direction of decreasing free energy of the system. In the case of solid-phase sintering of ceramic powders, the primary particles contained in the powders, depending on their particle size and calcination temperature, have a reduced surface area and interface with the calcination time, and grain growth occurs. It is known that: the smaller the particle size contained in the powder and the larger the difference between the particle size and the target particle size of the mass transfer, the easier it is for grain growth to occur.

[0003] It is also known that: generally, the fewer voids contained in the sintered body, the higher the strength of the ceramic sintered body, and the smaller the particle size contained in the sintered body, the higher the strength of the ceramic sintered body. Furthermore, it is known that: the fewer voids contained in the sintered body, the higher the translucency of the ceramic sintered body, and the more particles smaller than the wavelength of visible light contained in the sintered body, the higher the translucency of the ceramic sintered body.

[0004] Therefore, in order to achieve both the strength and translucency of ceramics, it is sought to have a sintered body with few voids, high density, and to keep the particle size contained in the sintered body small.

[0005] The voids existing between the ceramic particles are integrated as the grain growth progresses, and a part of them is discharged outside the sintered body, and a part of them remains inside the sintered body. In particular, when the grain growth is fast, the voids remaining inside the sintered body increase, so that obtaining a high-density sintered body becomes a problem. In addition, in the case where the ceramic contains polymorphs, density changes occur due to volume increase or decrease caused by temperature-dependent phase transitions, so that control of voids becomes a problem.

[0006] For example, zirconia has high strength and high toughness, and therefore, a zirconia sintered body (hereinafter sometimes also referred to as "partially stabilized zirconia sintered body") in which a small amount of yttrium oxide (yttrium oxide; Y₂O₃) is solid-solved as a stabilizer is used.

[0007] Among them, in the case of using a partially stabilized zirconia sintered body as a dental material, not only from the viewpoints of mechanical properties such as high strength and high toughness, but also from the aesthetic viewpoint, optical properties such as translucency and hue are required. So far, for partially stabilized zirconia sintered bodies, related studies have been conducted on zirconia sintered bodies having high density and strength of the sintered body and having translucency for the purpose of imitating natural teeth. Examples thereof include the following Patent Documents 1 and 2.

[0008] For example, Patent Document 1 discloses a translucent partially stabilized zirconia sintered body containing more than 4.0 mol% and 6.5 mol% or less of yttrium oxide.

[0009] In addition, Patent Document 2 discloses a granulated product in which the median particle size ratio of large particles (A) with a median particle size D50 of 0.2 to 12 μm to small particles (B) with a median particle size D50 of 0.01 to 0.3 μm is at most (A):(B)=40:1, and the mixing ratio is (A):(B)=0.01:99.9 to 99.9:0.01.

[0010] Prior Art Documents

[0011] Patent Documents

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-189524

[0013] Patent Document 2: US Patent Application Publication No. 2004 / 168610 Summary of the Invention

[0014] Problems to be Solved by the Invention

[0015] However, it is known that in Patent Document 1, only small particles with a primary particle size of 32 to 38 nm of raw material powder are used to obtain secondary aggregates with an average particle size of 0.4 μm to 0.5 μm. Therefore, the density of the green body is not high and the translucency is insufficient. In addition, it is known that when the median particle size ratio of large particles (A) to small particles (B) is too large as in Patent Document 2, during calcination, the small particles (B) are immediately absorbed by the large particles (A), and before the voids are discharged, coarse particles derived from the large particles (A) remain, and a sintered body with high density cannot be obtained, nor can a sintered body with high strength and high translucency be obtained. In addition, it is known that in the case of a powder in which the proportion of small particles (B) with a median particle size D50 of less than 0.1 μm is 100 parts by mass to 85 parts by mass, since they fuse with the large particles (A) with a size of 0.2 to 12 μm, during granulation, the small particles (B) hard-aggregate or form a hard shell, and a sintered body with high density cannot be obtained, nor can a sintered body with high strength and high translucency be obtained.

[0016] Therefore, an object of the present invention is to provide a green body for obtaining a zirconia sintered body capable of achieving both high strength and high translucency and a method for manufacturing the same.

[0017] Means for Solving the Problems

[0018] The inventors of the present invention have conducted extensive research to solve the above problems and found that a zirconia pre-sintered body containing zirconia and a stabilizer capable of suppressing the phase transformation of zirconia, having secondary aggregates with an average particle size of 275 nm or less, and the aggregates containing particles with an average particle size of 100 to 200 nm and 10 to 50 nm can solve the above problems. Through further extensive research, the present invention has been completed.

[0019] That is, the present invention includes the following technical solutions.

[0020] [1] A zirconia pre-sintered body comprising secondary aggregates with an average particle size of 275 nm or less,

[0021] wherein the secondary aggregates contain zirconia and a stabilizer capable of suppressing the phase transformation of zirconia, and

[0022] the secondary aggregates contain large particles with an average primary particle size of 100 nm or more and 200 nm or less and small particles with an average primary particle size of 10 nm or more and less than 60 nm.

[0023] [2] The zirconia pre-sintered body according to [1], wherein in the secondary aggregates, the content of the large particles is 15 to 85% by volume, and the content of the small particles is 15 to 85% by volume.

[0024] [3] The zirconia pre-sintered body according to [1] or [2], wherein the stabilizer is yttrium oxide.

[0025] [4] The zirconia pre-sintered body according to any one of [1] to [3], wherein the content of the stabilizer is 3.0 to 7.5 mol% based on the total moles of zirconia and the stabilizer,

[0026] and at least a part of the stabilizer is not dissolved in zirconia.

[0027] [5] The zirconia pre-sintered body according to any one of [1] to [4], wherein the density of the pre-sintered body is 2.75 g / cm 3 or more.

[0028] [6] The zirconia pre-sintered body according to any one of [1] to [5], wherein the average crystal grain size of the crystal grains contained in the pre-sintered body, i.e., the sintered body calcined at a calcination temperature of 1,500 °C or less for 2 hours, is 0.70 μm or less.

[0029] [7] The zirconia pre-sintered body according to any one of [1] to [6], wherein the density of the pre-sintered body, i.e., the sintered body calcined at a calcination temperature of 1,500 °C or less for 2 hours, is 5.8 g / cm 3 or more.

[0030] [8] The zirconia pre-sintered body according to any one of [1] to [7], wherein in the particle size distribution based on the number measured using an image obtained by photographing the aforementioned large particles and small particles with an electron microscope, there are two peaks, the particle size of the first peak representing the highest frequency particle size is 10 nm or more and less than 60 nm, and the particle size of the second peak is 60 nm or more and 200 nm or less.

[0031] [9] A method for manufacturing a zirconia pre-sintered body, which is a method for manufacturing a zirconia pre-sintered body containing zirconia and a stabilizer capable of suppressing the phase change of zirconia,

[0032] which uses a powder (A) containing secondary aggregates, the secondary aggregates contain a powder (a1) with an average primary particle size of 100 nm or more and 200 nm or less and a powder (a2) with an average primary particle size of 10 nm or more and less than 60 nm, and the average particle size is 275 nm or less,

[0033] The aforementioned secondary aggregates contain zirconia and a stabilizer capable of suppressing the phase change of zirconia.

[0034]

[10] The method for manufacturing a zirconia pre-sintered body according to [9], wherein the powder (A) containing the aforementioned secondary aggregates contains 15 to 85% by mass of the powder (a1) with an average primary particle size of 100 nm or more and 200 nm or less, and contains 15 to 85% by mass of the powder (a2) with an average primary particle size of 10 nm or more and less than 60 nm.

[0035]

[11] The method for manufacturing a zirconia pre-sintered body according to [9] or

[10] , wherein the aforementioned stabilizer is the powder (a1).

[0036]

[12] The method for manufacturing a zirconia pre-sintered body according to any one of [9] to

[11] , wherein the content rate of the aforementioned stabilizer is 3.0 to 7.5 mol% based on the total moles of zirconia and the stabilizer,

[0037] At least a part of the stabilizer is not dissolved in zirconia.

[0038]

[13] The method for manufacturing a zirconia pre-sintered body according to any one of [9] to

[12] , wherein the aforementioned stabilizer is yttrium oxide.

[0039]

[14] A method for manufacturing a powder, which is a method for manufacturing a powder for obtaining the zirconia pre-sintered body according to any one of [1] to [8], wherein,

[0040] a slurry containing secondary aggregates is manufactured, dried by spraying and granulated,

[0041] The secondary aggregate contains powder (a1) having an average primary particle size of 100 to 275 nm and powder (a2) having an average primary particle size of more than 10 nm and less than 60 nm, and has an average particle size of 275 nm or less.

[0042]

[15] A method for manufacturing a zirconia sintered body, wherein the zirconia pre-sintered body described in any one of [1] to [8] is calcined.

[0043] Advantages of the Invention

[0044] The zirconia pre-sintered body of the present invention can obtain a zirconia sintered body suitable for dental materials with both high strength and high translucency through calcination. In addition, the zirconia powder and the composition containing zirconia obtained by the method for manufacturing the powder of the present invention can suppress the occurrence of defects (deficiencies) in the zirconia formed body obtained during shaping, and thus have excellent shape retention. Description of the Drawings

[0045] Figure 1 SEM image of the zirconia pre-sintered body containing secondary aggregates described in Example 1.

[0046] Figure 2 SEM image of the zirconia powder described in Example 1.

[0047] Figure 3 SEM image of the zirconia powder with a hard shell formed in Comparative Example 4.

[0048] Figure 4 Particle size distribution (volume basis) of the zirconia slurry described in Examples 1 to 10 and Comparative Examples 1 to 3.

[0049] Figure 5A Particle size distribution (number basis) of the zirconia powder described in Example 1.

[0050] Figure 5B Particle size distribution (number basis) of the zirconia powder described in Comparative Example 4.

[0051] Figure 6A Particle size distribution (number basis) of the zirconia pre-sintered body described in Example 1.

[0052] Figure 6B Particle size distribution (number basis) of the zirconia pre-sintered body described in Comparative Example 4.

[0053] Figure 7 Particle size distribution (number basis) of the zirconia sintered body described in Example 1. Detailed Description of the Invention

[0054] The zirconia pre-sintered body of the present invention contains secondary aggregates with an average particle size of 275 nm or less. The aforementioned secondary aggregates contain zirconia and a stabilizer capable of suppressing the phase transformation of zirconia (hereinafter also simply referred to as "stabilizer"). Moreover, the aforementioned secondary aggregates contain large particles with an average primary particle size of 100 nm or more and 200 nm or less, and small particles with an average primary particle size of 10 nm or more and less than 60 nm.

[0055] The zirconia pre-sintered body of the present invention will be described. The zirconia pre-sintered body can be a precursor (intermediate product) of a zirconia sintered body. In the present invention, the zirconia pre-sintered body refers to a semi-sintered body obtained by agglomerating zirconia particles (powder) in a state where necking (fixation) has occurred but complete sintering has not yet taken place.

[0056] The zirconia pre-sintered body of the present invention contains secondary aggregates with an average particle size of 275 nm or less. The secondary aggregates are obtained by aggregating primary particles of large particles with an average particle size of 100 nm or more and 200 nm or less and small particles with an average particle size of 10 nm or more and less than 60 nm, respectively.

[0057] The average primary particle size of the large particles affects the density of the sintered body. Therefore, it is 100 nm or more and 200 nm or less, preferably 104 nm or more and 175 nm or less, more preferably 108 nm or more and 150 nm or less, and further preferably 110 nm or more and 135 nm or less. When the average primary particle size of the large particles is less than 100 nm, there is a possibility of strong aggregation with small particles and a sintered body with high density cannot be obtained. When the average primary particle size is more than 200 nm, the light transmittance after sintering may decrease. In addition, the average primary particle size of the small particles affects the average crystal grain size of the sintered body. Therefore, from the viewpoints of strength or light transmittance, it is 10 nm or more and less than 60 nm, preferably 15 nm or more and 50 nm or less, more preferably 20 nm or more and 50 nm or less, and further preferably 25 nm or more and 50 nm or less. When the average primary particle size of the small particles is less than 10 nm, there is a possibility of reducing the strength or light transmittance. When the average primary particle size is 60 nm or more, there is a possibility of reducing the light transmittance. Furthermore, from the viewpoints of the shape retention (shape retention) of the green body, the density, light transmittance, and strength of the sintered body, the average particle size of the secondary aggregates is 275 nm or less, preferably 265 nm or less, more preferably 255 nm or less, and further preferably 245 nm or less. In addition, from the viewpoint of obtaining a high-density pre-sintered body and sintered body, a morphology in which small particles are attached around the large particles is preferred. The morphology in which small particles are attached around the large particles can be confirmed by visual confirmation of, for example, an electron microscope image. It should be noted that the average particle size and average primary particle size of the present invention can be calculated by, for example, image analysis of images taken based on an electron microscope. The average primary particle sizes of the raw material powder, the green body obtained by shaping the raw material powder, and the secondary aggregates, large particles, and small particles contained in the pre-sintered body thereof can be measured by, for example, the methods described in the following examples.

[0058] The primary particles in the present invention refer to the smallest unit of bulk, including zirconia particles and stabilizer particles. In addition, the secondary aggregated particles refer to particles obtained by aggregating large particles with an average primary particle size of 100 nm or more and 200 nm or less and small particles with an average primary particle size of 10 nm or more and less than 60 nm. The large particles contain zirconia and / or a stabilizer, the small particles contain zirconia and / or a stabilizer, and at least one of the large particles or small particles contains a stabilizer. As a suitable embodiment, the following zirconia pre-sintered body can be cited, which has secondary aggregated particles in which the large particles contain zirconia particles and stabilizer particles (suitably yttria particles) and the small particles are composed of zirconia particles. As another suitable embodiment, the following zirconia pre-sintered body can be cited, which has secondary aggregated particles in which the large particles are composed of zirconia particles and the small particles contain zirconia particles and stabilizer particles (suitably yttria particles).

[0059] Regarding the zirconia pre-sintered body of the present invention, from the viewpoint of maintaining a small average crystal grain size of the sintered body and increasing the light transmittance and strength of the sintered body, in the aforementioned secondary aggregates, the content rate of the aforementioned large particles is preferably 15 to 85% by volume, more preferably 18 to 83% by volume, and still more preferably 20 to 80% by volume. In addition, the zirconia pre-sintered body of the present invention preferably contains 15 to 85% by volume of small particles, more preferably 17 to 82% by volume, and still more preferably 20 to 80% by volume. By being within these ranges, the average particle size of the secondary aggregation becomes 275 nm or less, the density of the pre-sintered body increases, and the strength and light transmittance of the sintered body can be improved. It should be noted that the content rates of the large particles and small particles of the present invention can be calculated, for example, by performing image analysis on images taken by an electron microscope.

[0060] The zirconia pre-sintered body of the present invention contains zirconia and a stabilizer capable of suppressing the phase transformation of zirconia. This stabilizer preferably can form partially stabilized zirconia. Examples of this stabilizer include oxides such as calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y2O3), cerium oxide (CeO2), scandium oxide (Sc2O3), niobium pentoxide (Nb2O5), lanthanum oxide (La2O3), erbium oxide (Er2O3), praseodymium oxide (Pr6O 11 , Pr2O3), samarium oxide (Sm2O3), europium oxide (Eu2O3), and thulium oxide (Tm2O3), and yttrium oxide is preferred. The content rate of the stabilizer in the zirconia pre-sintered body and its sintered body of the present invention can be measured, for example, by inductively coupled plasma (ICP; Inductively Coupled Plasma) optical emission spectrometry, X-ray fluorescence analysis (XRF), etc.

[0061] In the zirconia pre-sintered body and its sintered body of the present invention, from the viewpoints of the strength and light transmittance of the sintered body, the content rate of this stabilizer (preferably yttrium oxide) relative to the total moles of zirconia and the stabilizer is preferably 3.0 to 7.5 mol%, more preferably 3.5 to 7.0 mol%, and still more preferably 4.0 to 6.5 mol%. If the content rate of yttrium oxide is 3.0 mol% or more, the light transmittance of the sintered body can be improved, and if it is 7.5 mol% or less, a decrease in the strength of the sintered body can be suppressed.

[0062] In the zirconia pre-sintered body of the present invention, it is preferable that at least a part of the foregoing stabilizer is not dissolved in zirconia. That is, it is preferably present in such a manner that at least a part of the zirconia crystals is monoclinic. Whether a part of the stabilizer is not dissolved in zirconia can be confirmed by, for example, an X-ray diffraction (XRD; X-Ray Diffraction) pattern. When a peak derived from the stabilizer is confirmed in the XRD pattern of the zirconia pre-sintered body, there is a stabilizer that is not dissolved in zirconia in the zirconia pre-sintered body. When all of the stabilizer is dissolved, substantially no peak derived from the stabilizer can be confirmed in the XRD pattern. Among them, depending on conditions such as the crystal state of the stabilizer, even when there is no peak of the stabilizer in the XRD pattern, sometimes the stabilizer is not dissolved in zirconia. The main crystal systems of zirconia are tetragonal and / or cubic systems. When there is no peak of the stabilizer in the XRD pattern, it can be considered that most or substantially all of the stabilizer is dissolved in zirconia. In the zirconia pre-sintered body of the present invention, it is possible that all of the stabilizer is not dissolved in zirconia. It should be noted that in the present invention, solid solution of the stabilizer means that, for example, the elements (atoms) contained in the stabilizer are dissolved in zirconia.

[0063] In the zirconia pre-sintered body of the present invention, the existence rate f of yttrium oxide not dissolved in zirconia (hereinafter sometimes referred to as "undissolved yttrium oxide") y can be calculated according to the following formula (1).

[0064] f y = I y / (I 28 + I 30 ) * 100 (1)

[0065] In formula (1), I y represents the peak intensity of yttrium oxide near 2θ = 29° in the XRD pattern based on CuKα rays.

[0066] In addition, I 28 represents the peak area near 2θ = 28° where the main peak of the monoclinic system appears, and I 30 represents the peak area near 2θ = 30° where the main peak of the tetragonal or cubic system appears.

[0067] The existence rate f of undissolved yttrium oxide y is preferably greater than 0%, more preferably 1% or more, further preferably 2% or more, and particularly preferably 3% or more. The upper limit of the existence rate f of undissolved yttrium oxide y depends on the content rate of yttrium oxide in the pre-sintered body. When the content rate of yttrium oxide is 7.5 mol% or less based on the total moles of zirconia and yttrium oxide, f y can be set to 15% or less. For example, when the content rate of yttrium oxide is 3.0 mol% or more and less than 4.5 mol%, fy can be set to 7% or less. When the content rate of yttrium oxide is 4.5 mol% or more and less than 5.5 mol%, f y can be set to 10% or less. When the content rate of yttrium oxide is 5.5 mol% or more and less than 6.5 mol%, f y can be set to 11% or less. When the content rate of yttrium oxide is 6.5 mol% or more and 7.5 mol% or less, f y can be set to 15% or less.

[0068] When the content rate of yttrium oxide is 3.0 mol% or more and less than 4.5 mol%, f y is preferably 2% or more, more preferably 3% or more, further preferably 4% or more, and particularly preferably 5% or more. When the content rate of yttrium oxide is 4.5 mol% or more and less than 5.8 mol%, f y is preferably 3% or more, more preferably 4% or more, further preferably 5% or more, still further preferably 6% or more, and particularly preferably 7% or more. When the content rate of yttrium oxide is 5.8 mol% or more and 7.5 mol% or less, f y is preferably 4% or more, more preferably 5% or more, further preferably 6% or more, still further preferably 7% or more, and particularly preferably 8% or more.

[0069] In addition, in the zirconia pre-sintered body of the present invention, peaks of tetragonal and cubic crystal systems can be substantially not detected.

[0070] From the viewpoint of improving the strength and light transmittance of the sintered body, the density of the zirconia pre-sintered body of the present invention is preferably 2.75 g / cm 3 or more, more preferably 2.85 g / cm 3 or more, and further preferably 2.95 g / cm 3 or more. By making the density of the zirconia pre-sintered body 2.75 g / cm 3 or more, the light transmittance of the zirconia sintered body can be 8.6 or more, and the biaxial bending strength of the zirconia sintered body can be 850 MPa or more. The measurement methods of the light transmittance and biaxial bending strength of the zirconia sintered body can be measured by the methods described in the following examples.

[0071] When the zirconia pre-sintered body of the present invention is calcined at a calcination temperature of 1,500 °C or lower for 2 hours, the average crystal grain size of the crystal grains contained in the sintered body is preferably 0.70 μm or less, more preferably 0.68 μm or less, and further preferably 0.65 μm or less. By making the average particle size of the particles contained in the sintered body 0.70 μm or less, the light transmittance of the zirconia sintered body can be 8.6 or more, and the biaxial bending strength of the zirconia sintered body can be 850 MPa or more. In addition, even when the average particle size is small, if the density of the pre-sintered body is less than 2.75 g / cm 3 , the light transmittance will not increase, so it is not preferred. In addition, as the zirconia pre-sintered body of the present invention, the density of the sintered body when calcined at a calcination temperature of 1,500 °C or lower for 2 hours is preferably 5.8 g / cm 3 or more.

[0072] Regarding the zirconia pre-sintered body of the present invention, when measuring the average particle size by image analysis of the images taken by an electron microscope (such as SEM) as described in the following examples, from the viewpoint of providing a zirconia sintered body that can balance high strength and high light transmittance, it is preferably to have two peaks in the particle size distribution based on the number measured using the images taken by the electron microscope of large and small primary particles. In the present invention, a peak means that the frequency is at least 5% or more, and from the viewpoint of obtaining more excellent strength and light transmittance, it is preferably 6% or more, more preferably 7% or more, and further preferably 8% or more. In addition, in the particle size distribution based on the number, it is preferred that: the particle size of the first peak representing the highest frequency particle size (mode particle size) is 10 nm or more and less than 60 nm, and the particle size of the second peak is 60 nm or more and 200 nm or less. From the viewpoint of obtaining more excellent strength and light transmittance, it is more preferred that: the average particle size of the aforementioned first peak is 10 nm or more and 50 nm or less, and the frequency of the second peak is 8% or more. Further preferably, the average particle size of the aforementioned first peak is 10 nm or more and 50 nm or less, and the second peak is 9% or more.

[0073] Next, the composition containing zirconia for manufacturing the zirconia pre-sintered body of the present invention and the powder used for manufacturing the composition containing zirconia will be described.

[0074] The composition containing zirconia becomes the precursor of the above-mentioned zirconia pre-sintered body of the present invention. The content rates of zirconia and the stabilizer in the composition containing zirconia are calculated according to the content rate of the specified zirconia pre-sintered body, and the content rates in the composition containing zirconia and the zirconia pre-sintered body are the same. In the composition containing zirconia, the measurement method of the content rate of the stabilizer can also be measured using the same measurement method as that of the zirconia pre-sintered body.

[0075] The zirconia-containing composition further includes powder, a fluid obtained by adding the powder to a solvent, and a formed body obtained by shaping the powder into a specified shape. When the zirconia-containing composition has a powder form, it may be an aggregate of powders. The powder is formed by aggregation of primary particles.

[0076] The primary particles in the present invention refer to the smallest unit blocks. For example, the primary particles refer to: in an electron microscope (such as a scanning electron microscope), spherical bodies that do not bond to each other and appear to be in a separable state. The primary particles include zirconia particles and stabilizer particles. In addition, the particles obtained by aggregating the primary particles are regarded as secondary particles.

[0077] The particles constituting the zirconia-containing composition in the present invention preferably have secondary aggregates (secondary aggregated particles) as the main body. "Having... as the main body" means that the content rate of the secondary aggregates is 50% by mass or more in the zirconia-containing composition, preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% by mass or more. The average particle diameter of the secondary aggregated particles is preferably 100 nm or more and 275 nm or less, more preferably 100 nm or more and 265 nm or less, further preferably 100 nm or more and 255 nm or less, and particularly preferably 100 nm or more and 245 nm or less. If the average particle diameter is 100 nm or more, the adhesion force of the secondary aggregated particles can be suppressed from increasing, and it is possible to prevent the secondary aggregated particles from aggregating with each other and causing hypertrophy of the secondary aggregation. If the average particle diameter of the secondary aggregated particles exceeds 275 nm, the density of the formed body will not increase due to the skeleton effect (the effect of particles contacting and supporting each other) during pressure forming, and the strength and / or light transmittance after sintering will decrease, so it is not preferred. The method for measuring the average particle diameter of the secondary aggregated particles is as described in the following examples.

[0078] The particles constituting the secondary aggregate particles include large particles having an average primary particle diameter of 100 nm or more and 200 nm or less and small particles having an average primary particle diameter of 10 nm or more and less than 60 nm. The average primary particle diameter of the large particles is preferably 104 nm or more and 175 nm or less, more preferably 108 nm or more and 150 nm, and further preferably 110 nm or more and 135 nm or less. The method for measuring the average primary particle diameters of the large particles and the small particles is as described in the following examples. When the average primary particle diameter of the large particles is less than 100 nm, there is a possibility of strong aggregation with the small particles, forming a hard shell on the powder surface and resulting in a composition with low density. When the average primary particle diameter of the large particles is greater than 200 nm, the sintering ability of the green compact becomes low. If the sintering temperature is not set high, it is difficult to increase the density after calcination, and it may not be possible to obtain high light transmittance and high strength. The average primary particle diameter of the small particles is preferably 15 nm or more and 50 nm or less, more preferably 20 nm or more and 50 nm or less, and further preferably 25 nm or more and 50 nm or less. When the average primary particle diameter of the small particles is less than 10 nm, a hard shell is formed on the powder surface, and a composition with high density cannot be obtained, so it is not preferred. When the average particle diameter of the small particles is greater than 50 nm, it is not possible to lower the calcination temperature, so it is not preferred. In addition, in visual confirmation of, for example, an electron microscope image, it is preferably in a form in which small particles are attached around the large particles. Furthermore, in order to arrange small particles around the large particles, it is preferable to control the surface potentials of the large particles and the small particles to opposite signs and design them to attract each other.

[0079] The average particle diameter of the secondary aggregate varies depending on the powder mixing ratio of the large particles and the small particles. Therefore, in the aforementioned secondary aggregate, the content of the particles is preferably 15 to 85% by mass, more preferably 18 to 83% by mass, and further preferably 20 to 80% by mass. When the large particles are more than 85% by mass, the attachment of the small particles to the large particles may decrease. When it is less than 15% by mass, the proportion of the small particles is too large, and there is a possibility of forming a hard shell on the powder surface and resulting in a composition with low density.

[0080] Among the zirconia in the composition containing zirconia, 50% or more, preferably 70% or more, more preferably 80% or more, and further preferably 90% or more of the zirconia can be in the form of powder.

[0081] The loose bulk density of the composition containing zirconia is preferably 1.0 g / cm 3 or more, more preferably 1.1 g / cm 3 or more, further preferably 1.2 g / cm 3 or more, and particularly preferably 1.3 g / cm 3As above. The loose bulk density can be measured in accordance with JIS R9301-2-3.

[0082] The tapped bulk density of the composition containing zirconia is preferably 1.3 g / cm 3 or more, more preferably 1.4 g / cm 3 or more, and further preferably 1.5 g / cm 3 or more. The tapped bulk density can be measured in accordance with JIS R 9301-2-3.

[0083] The composition containing zirconia may contain a binder.

[0084] Examples of the aforementioned binder include, for example, organic binders. Examples of organic binders include commonly used acrylic binders, acrylic binders, alkane binders, fatty acid binders, polyvinyl alcohol binders, and the like. Among these organic binders, substances having a carboxyl group or carboxylic acid derivatives in the molecular chain are preferred, more preferably acrylic binders (such as polyacrylic acid, etc.), and further preferably water-soluble polyacrylates. The polyacrylate may be obtained by copolymerizing acrylic acid or methacrylic acid with maleic acid, or may contain sulfonic acid. Examples of the cation of the salt include sodium, ammonium, and the like.

[0085] The content rate of the binder contained in the composition containing zirconia is important for adjusting the distance between primary particles in the composition containing zirconia. As the content rate of the binder, in the entire composition containing zirconia, it is preferably 1.0 to 3.0% by mass, more preferably 1.2 to 2.8% by mass, and further preferably 1.4 to 2.6% by mass. When the content rate of the binder in the entire composition containing zirconia is less than 1.0% by mass, the molded body may be defective. In addition, when it exceeds 3.0% by mass, the density of the molded body may not increase, and the strength and / or translucency of the sintered body may decrease.

[0086] The zirconia-containing composition may optionally contain additives such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (Al2O3), titanium oxide (TiO2), silica (SiO2), dispersants (such as polyacrylic acid, 3-phenylpropionic acid, etc.), and defoamers. These components can be used individually or in combination of two or more. As the aforementioned pigments, examples include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Er. As the aforementioned composite pigments, examples include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, (Co,Zn)Al2O4, etc. As the aforementioned fluorescent agents, examples include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, BaMgAl 10 O 17 :Eu, etc.

[0087] The aforementioned additives can be added during mixing or grinding, or can be added after grinding.

[0088] As a method for manufacturing a zirconia pre-sintered body, examples include the following manufacturing method: It uses a powder (A) containing secondary aggregates, the secondary aggregates contain a powder (a1) with an average primary particle size of 100 nm or more and 200 nm or less and a powder (a2) with an average primary particle size of 10 nm or more and less than 60 nm, and the average particle size is 275 nm or less. The aforementioned secondary aggregates contain zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia. First, the manufacturing process of the powder will be described.

[0089] The manufacturing method of the powder (A) is not particularly limited, and processes such as a breakdown process of micronizing by pulverizing coarse particles, a build-up process of synthesizing from atoms to ions through a nucleation and growth process, etc. can be adopted. As the manufacturing method of the powder (A), the following methods can be cited as examples: manufacturing a slurry containing secondary aggregates, spray-drying and granulating to obtain the powder (A), the secondary aggregates containing powder (a1) with an average primary particle size of 100 nm or more and 200 nm or less and powder (a2) with an average primary particle size of 10 nm or more and less than 60 nm, and having an average particle size of 275 nm or less. The powder (a1) can be a zirconia powder, a stabilizer powder, or can contain both. In addition, when the powder (a1) contains a zirconia powder, the powder (a2) preferably contains a stabilizer powder. When the powder (a1) contains a stabilizer powder, the powder (a2) preferably contains a zirconia powder. The powder (a1) corresponds to the aforementioned large particles. The powder (a2) corresponds to the aforementioned small particles. The aforementioned secondary aggregates contain particles, and the particles contain zirconia and a stabilizer capable of suppressing the phase change of zirconia.

[0090] For example, first, zirconia and a stabilizer are mixed in a predetermined ratio to prepare a mixture (mixing step). Powders of predetermined raw material compounds are selected in such a way that powder (a1) with an average primary particle size of 100 nm or more and 200 nm or less and powder (a2) with an average primary particle size of 10 nm or more and less than 60 nm can be obtained. When the stabilizer is yttrium oxide, the mixing ratio of zirconia and yttrium oxide can be mixed in such a way that the aforementioned content rate of yttrium oxide is achieved. The mixing of the powder (a1) and the powder (a2) can be dry mixing or wet mixing. The composition containing zirconia can be pulverized in such a way that the particles contained in the slurry become a desired particle size (for example, about 100 nm) (pulverizing step). The mixing step and the pulverizing step can be carried out in the same step. Pulverization can be carried out, for example, after dispersing the composition and a binder in a solvent such as water (dispersion step), using a ball mill, a bead mill, etc. to pulverize the composition. After the mixing step and / or the pulverizing step, the mixture is dried by spray drying using a spray dryer or the like, and a powder form as described above can be formed (drying step). Thus, a zirconia-containing composition (powder (A)) in the powder form according to the present invention can be manufactured.

[0091] In the particle size distribution based on the number measured using an image obtained by photographing the powder (A) with an electron microscope, it preferably has two peaks. In the present invention, the frequency of the peak of the powder (A) is at least 3% or more, and from the viewpoint of obtaining more excellent strength and translucency, it is preferably 4% or more, more preferably 5% or more, and further preferably 6% or more. In addition, in the particle size distribution of the powder (A) based on this number basis, it is preferable that: the particle size of the first peak representing the highest frequency particle size (mode particle size) is 10 nm or more and less than 60 nm, and the particle size of the second peak is 60 nm or more and 200 nm or less. From the viewpoint of obtaining more excellent strength and translucency, it is more preferable that: the average particle size of the aforementioned first peak is 10 nm or more and 50 nm or less, and the frequency of the second peak is 4% or more. Further preferably, the average particle size of the aforementioned first peak is 10 nm or more and 50 nm or less, and the second peak is 5% or more. In addition, in the particle size distribution of the powder (A) based on this number basis, the difference in frequency (%) between the first peak and the second peak representing the highest frequency particle size (mode particle size) is preferably 20% or less, more preferably 18% or less, and further preferably 15% or less. In addition, the difference in the aforementioned frequency (%) preferably exceeds 0%, more preferably 0.5% or more, and further preferably 1.0% or more.

[0092] In the pulverization step, it is preferable to use pulverization media of a small size. For example, it is preferable to use pulverization media of 100 μm or less. In addition, it is preferable to perform classification after pulverization.

[0093] It is preferable to prepare zirconia and a stabilizer separately. For example, zirconia and the stabilizer do not precipitate simultaneously (in the same step), but it is preferable that the preparation step (such as the manufacturing step) of zirconia and the preparation step (such as the manufacturing step) of the stabilizer are separate independent steps. Thereby, it is possible to suppress the solid solution of the stabilizer in zirconia in the manufacturing step of the green compact described later.

[0094] The powder (A) can be formed into a formed body by applying an external force. The forming method is not limited to a specific method, and a suitable method can be appropriately selected according to the purpose. Forming can be performed, for example, by pressure forming, injection molding, stereolithography, etc. In addition, multi-stage forming can be performed. For example, after pressure forming a composition containing zirconia, CIP treatment can be further performed.

[0095] The aforementioned formed body can have a disk shape, a rectangular parallelepiped shape, or a dental product shape (such as a crown shape).

[0096] For example, it may be a columnar compact obtained by filling a mold with zirconia powder (the aforementioned powder (A) containing zirconia and a stabilizer capable of suppressing the phase transformation of zirconia) and compacting it by uniaxial pressing. The higher the surface pressure during the pressure forming, the higher the density of the compact. On the other hand, if the density of the compact is too high, the zirconia pre-sintered body becomes hard. Therefore, the surface pressure for pressure forming is preferably 30 to 200 MPa. When the surface pressure of the pressing is 30 MPa or more, the shape retention of the compact is excellent. In addition, when it is 200 MPa or less, the density of the compact does not increase excessively, and it is easier to prevent hardening.

[0097] The aforementioned compact also includes a compact densified by high-temperature pressure treatment such as CIP (Cold Isostatic Pressing) treatment. From the same viewpoint as above, the water pressure is preferably 30 to 200 MPa.

[0098] The zirconia pre-sintered body of the present invention becomes a precursor (intermediate product) of the zirconia sintered body. The pre-sintered body also includes a material obtained by forming processing. The zirconia pre-sintered body of the present invention also includes, for example, a dental product (such as a crown-shaped prosthesis) obtained by processing a pre-sintered zirconia disk using a CAD / CAM (Computer-Aided Design / Computer-Aided Manufacturing) system.

[0099] The content ratios of zirconia and the stabilizer in the zirconia pre-sintered body of the present invention are the same as those in the composition or compact containing zirconia before the zirconia pre-sintered body is produced. From the viewpoints of the strength and translucency of the sintered body made from the zirconia pre-sintered body of the present invention, the stabilizer is preferably yttria. The compact is obtained by forming (for example, pressure forming) a composition containing zirconia, and the content ratios of zirconia and the stabilizer can be regarded as the same as those of the composition containing zirconia.

[0100] The un-dissolved ratio of the stabilizer in the zirconia pre-sintered body of the present invention is, as described above, calculated based on the existence rate f of un-dissolved yttria y and more depends on the pre-sintering temperature.

[0101] The pre-sintering temperature in the manufacturing method of the zirconia pre-sintered body of the present invention is preferably 830 to 1080 °C, more preferably 850 to 1050 °C, and further preferably 895 to 1000 °C. When the pre-sintering temperature is less than 830 °C, the strength and hardness of the pre-sintered body may be insufficient, and the machinability may decrease. In addition, when the pre-sintering temperature is greater than 1080 °C, the strength and hardness of the pre-sintered body may increase, the machinability may decrease, and the dissolved amount of the stabilizer may increase depending on the content ratio of the stabilizer, generating a phase that thermally transforms into the tetragonal and / or cubic crystal systems.

[0102] If maintained for a specified time at the highest pre-firing temperature, the hardness of the pre-fired body sometimes falls within a preferred range, and the machinability is good, so this is preferred. The pre-firing conditions depend on the density of the pre-fired body, the average particle size of the pre-fired body, and the amount of binder, and it is preferably maintained at the highest pre-firing temperature for 30 minutes to 6 hours. In addition, the heating rate and the cooling rate are preferably 300 °C / minute or less.

[0103] The zirconia pre-fired body of the present invention can be made into a machined body by performing machining. The machining method is not limited to a specific method, and a suitable method can be appropriately selected according to the purpose. For example, a zirconia disk, which also belongs to the pre-fired body, can be machined into the shape of a dental product (such as a crown-shaped prosthesis) using a CAD / CAM system to make a machined body.

[0104] The surface smoothness of the machined body can be improved using tools such as abrasive materials (e.g., Pearl Surface (registered trademark), manufactured by Kuraray Noritake Dental Co., Ltd.).

[0105] By subjecting the zirconia pre-fired body or its machined body of the present invention to a sintering process of calcination at a temperature at which zirconia particles are sintered, a zirconia sintered body (hereinafter sometimes simply referred to as "zirconia sintered body" or "sintered body") can be produced. From the viewpoint of controlling grain growth to obtain a sintered body with high translucency and high strength, the calcination temperature is preferably 1300 to 1600 °C, more preferably 1350 to 1550 °C, and further preferably 1350 to 1450 °C. Within the above range, the average crystal grain size of the crystal grains contained in the sintered body becomes 0.7 μm or less, and the density of the sintered body becomes 5.8 g / cm 3 Thus, high translucency and high strength can be obtained.

[0106] In the aforementioned sintering process, the holding time at the sintering temperature (e.g., the highest calcination temperature) is preferably less than 120 minutes, more preferably 90 minutes or less, further preferably 75 minutes or less, still further preferably 60 minutes or less, particularly preferably 45 minutes or less, and most preferably 30 minutes or less. This holding time is preferably 1 minute or more, more preferably 5 minutes or more, and further preferably 10 minutes or more.

[0107] The zirconia pre-sintered body according to the present invention does not reduce the light transmittance and strength of the produced zirconia sintered body, and can shorten the calcination time for producing the sintered body. In particular, it is possible to shorten the holding time at the highest calcination temperature for producing the sintered body (short-time sintering). Thereby, the production efficiency can be improved. When the zirconia pre-sintered body of the present invention is applied to dental products, the size of the dental products used in treatment can be determined, the time from cutting to the start of treatment using the dental products can be shortened, and the time burden on patients can be reduced. In addition, the energy cost can be reduced.

[0108] In the sintering process, the holding time at the sintering temperature (for example, the highest calcination temperature) can be set to 25 minutes or less, 20 minutes or less, or 15 minutes or less, for example.

[0109] The heating rate and cooling rate in the sintering process are preferably set in such a way that the time required for the sintering process is shortened. For example, the heating rate can be set according to the performance of the calcination furnace so as to reach the highest calcination temperature in the shortest time. The heating rate up to the highest temperature can be set to 10 °C / min or more, 50 °C / min or more, 100 °C / min or more, 120 °C / min or more, 150 °C / min or more, or 200 °C / min or more, for example. The cooling rate is preferably set to a rate such that no defects such as cracks occur in the sintered body. For example, after the heating is completed, the sintered body can be naturally cooled to room temperature.

[0110] The zirconia sintered body obtained by sintering the zirconia pre-sintered body or its machined body of the present invention will be described. The zirconia sintered body can be, for example, a substance obtained by sintering zirconia particles in a sintered state. The relative density of the zirconia sintered body is preferably 99.5% or more. The relative density can be calculated in the form of the ratio of the measured density measured by the Archimedes method to the theoretical density. The relative density means: for a formed body in which powder is filled into a specific mold and formed into a specific shape, the density d1 of the sintered body obtained by calcining the formed body at a high temperature is divided by the theoretical (void-free inside) zirconia density d2.

[0111] The zirconia sintered body includes not only a sintered body obtained by sintering formed zirconia particles under normal pressure or unpressurized conditions, but also a sintered body obtained by densifying it through high-temperature pressure treatment such as HIP (Hot Isostatic Pressing) treatment.

[0112] Regarding the density of the zirconia sintered body, the higher the density, the fewer the internal voids and the less likely light scattering occurs. Therefore, from the viewpoint of improving light transmittance, it is preferably 5.80 g / cm 3 Above, more preferably 5.82 g / cm3 More preferably, it is 5.87 g / cm³ or more. 3 More preferably, the zirconia sintered body is substantially void-free.

[0113] The higher the content of particles having an average crystal grain size smaller than the wavelength of visible light among the crystal grains contained in the zirconia sintered body, the higher the light transmittance and the higher the strength, and thus it is preferred. The range is preferably 0.70 μm or less, more preferably 0.68 μm or less, and still more preferably 0.65 μm or less. The average crystal grain size of the crystal grains contained in the zirconia sintered body can be measured by the method described in the examples below.

[0114] The content ratio of zirconia and the stabilizer in the zirconia sintered body is the same as the content ratio in the composition and / or the pre-sintered body before producing the sintered body. Regarding the crystal system of zirconia in the sintered body, the proportion of the monoclinic crystal system is preferably 10% or less, more preferably 5% or less, and still more preferably substantially free of (regarded as 0%). The crystal systems other than the monoclinic crystal system are the tetragonal crystal system and / or the cubic crystal system.

[0115] Regarding the solid solution ratio of the stabilizer in the zirconia sintered body, it is preferred that 95% or more of the contained stabilizer is solid-solved in zirconia, and more preferably substantially all of the stabilizer is solid-solved. The existence rate f of yttrium oxide not solid-solved y is preferably 5% or less, more preferably 1% or less, and still more preferably substantially all is solid-solved (0%).

[0116] The higher the strength of the zirconia sintered body, the more preferred. For example, the biaxial flexural strength is preferably 800 MPa or more, more preferably 820 MPa or more, and still more preferably 840 MPa or more. The biaxial flexural strength can be measured in accordance with ISO 6872:2015 and can be measured by, for example, the method described in the examples below.

[0117] The light transmittance of the zirconia sintered body is preferably 8.6 or more, more preferably 10 or more, and still more preferably 11 or more. The light transmittance mentioned here means: for the L* value of lightness (color space) in the L*a*b* color system (JIS Z 8781—4: 2013), the L* value measured with the background of a 1.2-mm-thick specimen set to white is taken as the first L* value, and for the same specimen after measuring the first L* value, the L* value measured with the background of the specimen set to black is taken as the second L* value, and the value obtained by subtracting the second L* value from the first L* value. Regarding the method for producing the specimen, first, the powder (composition) can be compression-molded so that the thickness of the sintered body becomes 1.2 mm, and then, a disk-shaped green compact with a diameter of 19 mm, for example, can be produced by CIP molding. Then, the green compact can be calcined under specified calcination conditions to produce a sintered body with a thickness of 1.2 mm for the specimen. Regarding the measurement of the L* value, after applying a contact liquid to the surface of the specimen, a color difference meter (for example, the dental color measuring device "Crystal Eye CE100-DC / JP" and the analysis software "Crystal Eye" (manufactured by Olympus Corporation)) can be used to measure the L* values of the black background and the white background. As the contact liquid, a contact liquid with a refractive index nD of 1.60 measured at a measurement wavelength of 589 nm (sodium D line), for example, can be used.

[0118] The zirconia sintered body can be a green compact with a specified shape. For example, the sintered body can have a disk (round disk) shape, a rectangular parallelepiped shape, or a dental product shape (for example, a crown shape).

[0119] The manufacturing methods of the composition, powder, green compact, pre-sintered body, machined body, and sintered body described in this specification are not limited to the above as long as they can obtain the desired constitution and effects of the present invention, and various known methods can be applied.

[0120] The pre-sintered body of the present invention can be suitably used for zirconia processed products that require strength and / or aesthetic properties after calcination, such as dental materials, optical fiber connectors, and smartphone cases.

[0121] Examples

[0122] Next, the present invention will be described in more detail by way of examples, but the present invention is not limited by any of these examples.

[0123] <Measurement of the average particle size of the powder>

[0124] The powders obtained in the following Examples and Comparative Examples were infiltrated into a two-component curable epoxy resin (trade name "MA2+", manufactured by Maywa Foasis Co., Ltd.) in a vacuum and embedded for 12 hours. The resulting cured product was polished with abrasive paper to expose the powder cross-section. Using a high-resolution analytical scanning electron microscope (trade name "SU-70", manufactured by Hitachi, Ltd.), an image of the surface (SEM image) was obtained. For the obtained image, the average particle size was calculated by image analysis and used as the "average particle size of the secondary aggregates of the powder". The measurement of the average particle size used the image analysis software "Image-Pro Plus" manufactured by Pfeiffer Vacuum. After binarizing the read SEM image, the grain boundaries of each crystal grain were marked in the obtained image, and then the particles were identified from the field of view (area). The particle size obtained by Image-Pro Plus refers to the diameter passing through the center of gravity of the particle. The average particle size refers to the particle size obtained by measuring and averaging the lengths of the line segments connecting the outline lines passing through the center of gravity obtained from the particle outline line at a scale of 2 degrees with the center of gravity as the center. For one sample of each Example and Comparative Example, the average value of 10 fields of view was used as the average particle size of the powder. In addition, for the primary particle size of the particles in the secondary aggregates, in the present invention, since the particle size distribution based on the number has two peaks, peak separation was performed to obtain the average particle size of each as the "average particle size" of the large particles and small particles. Regarding peak separation, based on the particle size distribution data obtained by image analysis, a Gaussian function and a Lorentz function were used to fit in the form of two peaks, and the average particle size of each single peak was calculated. Peak separation can also use, for example, the "Peak Separation" file at the following link.

[0125] https: / / www.jie.or.jp / publics / index / 497 /

[0126] Regarding the particle size distribution (number basis) of the powder described in Example 1, it is shown in Figure 5A , and regarding the particle size distribution (number basis) of the powder described in Comparative Example 4, it is shown in Figure 5B . The vertical axis represents the frequency (%), and the horizontal axis represents the particle size (nm).

[0127] <Measurement of the median particle size D50 of the particles in the slurry>

[0128] The median particle size D50 was measured as follows: Using a laser diffraction / scattering particle size distribution measuring device (trade name "Partica LA-950") manufactured by Horiba, Ltd., the slurry diluted with water was irradiated with ultrasonic waves for 30 minutes, and then measured based on the volume while being in contact with ultrasonic waves. The particle size at which the cumulative frequency in the obtained measurement results became 50% was calculated using software and used as the median particle size D50.

[0129] <Evaluation method for shape retention of formed body>

[0130] The powder obtained in the following Examples or Comparative Examples was filled into a columnar mold and clamped from above and below using the mold, and uniaxial pressing was performed until the stress reached 33 MPa. For the formed body taken out after pressing, visually confirm whether the corners of the rectangle are lacking (n = 5). The case where more than 2 out of 5 have a lack (defect) of 0.7 mm or more was regarded as having no shape retention and evaluated as "×", and the case where there is no lack was regarded as having excellent shape retention and evaluated as "○".

[0131] <Measurement of average particle size in pre-sintered body>

[0132] Using the pre-sintered body obtained in the following Examples or Comparative Examples, a surface image was obtained using a scanning electron microscope (trade name "VE-9800", manufactured by Keyence Corporation). For the obtained image, the average particle size was measured by image analysis and used as the "average particle size of the secondary aggregates of the pre-sintered body". The measurement of the average particle size was performed using the image analysis software "Image-Pro Plus" manufactured by Hitachi High-Technologies Corporation. The particle size obtained by Image-Pro Plus refers to the diameter passing through the center of gravity of the particle, and the average particle size refers to the particle size obtained by measuring and averaging the length of the line segment connecting the outer shape lines passing through the center of gravity obtained from the outer shape line of the particle at a scale of 2 degrees with the center of gravity as the center. For one sample of each Example and Comparative Example, the average value of 10 fields of view was used as the average particle size of the pre-sintered body. In addition, for the primary particle size of the particles in the secondary aggregates, in the present invention, since the particle size distribution has two peaks, peak separation was performed to obtain the respective average particle sizes as the "average particle sizes" of large particles and small particles. The SEM image of the zirconia pre-sintered body described in Example 1 is shown in Figure 1 . In addition, the particle size distribution (number basis) of the zirconia pre-sintered body described in Example 1 is shown in Figure 6A , and the particle size distribution (number basis) of the zirconia pre-sintered body described in Comparative Example 4 is shown in Figure 6B . The vertical axis represents the frequency (%), and the horizontal axis represents the particle size (nm) of the primary particles contained in the zirconia pre-sintered body.

[0133] <Discrimination method for non-partial solid solution of zirconia and stabilizer in zirconia pre-sintered body>

[0134] Regarding the determination that at least a part of the stabilizer in the zirconia pre-sintered body of the present invention has not undergone solid solution, a 2-mm flat plate is made from the zirconia pre-sintered body. For this flat plate, using a fully automatic horizontal multi-purpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and X-ray analysis integrated software (SmartLab Studio II, manufactured by Rigaku Corporation), measurements are carried out under the following conditions, and the presence or absence of peaks is confirmed for the peaks near 29°. Regarding the presence or absence of peaks, when the intensity of the peak at 2θ = 10 to 90° is set to 100, if the peak of the stabilizer is 1 or more, it is determined that solid solution has not occurred and it exists, and is denoted as "○", if it is less than 1, it is regarded that solid solution has occurred and it does not exist in the form of the stabilizer monomer, and is denoted as "×".

[0135] X-ray source: Cu Kα

[0136] Goniometer length: 300 mm

[0137] Optical system: Concentration method

[0138] Detector: High-speed one-dimensional X-ray detector (D / teX Ultra250)

[0139] Monochromatization: Kβ filter

[0140] Tube voltage: 40 kV

[0141] Tube current: 30 mA

[0142] Scanning axis: 2θ / θ

[0143] Scanning speed: 0.2° / minute

[0144] Sampling pitch: 0.01°

[0145] <Method for measuring the content rate [volume%] of primary particles in the secondary aggregates in the pre-sintered body>

[0146] Based on the particle size of each individual particle obtained by Image-Pro Plus, the volume of each individual particle is calculated. Since the particle size distribution has two peaks, peak separation is performed to obtain the volume% of each.

[0147] <Method for measuring the density of the pre-sintered body>

[0148] The pre-sintered body obtained through the following examples or comparative examples is made into a cuboid shape with a bottom surface of 14 mm × 14 mm, and using a micrometer and a precision balance, the (mass of the pre-sintered body) / (volume of the pre-sintered body) is used to obtain (the average value of n = 3).

[0149] <Method for measuring the average crystal grain size in the sintered body>

[0150] For the sintered compacts obtained through the following Examples or Comparative Examples, images of the surface were obtained using a scanning electron microscope (trade name "VE-9800", manufactured by Keyence Corporation). For the obtained images, the average crystal grain size was calculated through image analysis. The measurement of the average crystal grain size used the image analysis software "Image-Pro Plus" manufactured by Hitachi High-Technologies Corporation. The SEM image read in was binarized, the brightness range was adjusted to make the grain boundaries clear, and the grains were identified from the field of view (area). The crystal grain size obtained through Image-Pro Plus refers to the diameter passing through the center of gravity of the crystal grain, and the average crystal grain size refers to the grain size obtained by measuring and averaging at 2-degree intervals with the center of gravity as the center for the length of the line segment obtained by connecting the outer contours passing through the centers of gravity obtained from the outer contours of the grains. For one sample of each Example and Comparative Example, the average value of 10 fields of view was used as the average crystal grain size in the sintered compact. The measurement results of the particle size distribution (number basis) of the average crystal grain size in the zirconia sintered compact described in Example 1 are shown in Figure 7 . In Figure 7 , the vertical axis represents the number, and the horizontal axis represents the diameter (μm).

[0151] <Method for Measuring the Density of the Sintered Compact>

[0152] For the columnar sintered compacts obtained through the following Examples or Comparative Examples, the dimensions were accurately measured using a micrometer, the mass was measured using an analytical balance, and the density was calculated as (mass of the sintered compact) / (volume of the sintered compact) (average value of n = 3). The density of the sintered compact is evaluated as "○" when it is 5.80 g / cm 3 or higher, and as "×" when it is less than 5.80 g / cm 3 .

[0153] <Evaluation of the Translucency of the Sintered Compact>

[0154] For the sintered compacts obtained through the following Examples or Comparative Examples, they were ground into flat specimens with a thickness of 1.2 mm, and a spectrophotometer (trade name "Crystal Eye") manufactured by Olympus Corporation was used to measure the lightness (L w * ) when measuring the chromaticity under a white background using an LED light source under the condition of a seven-band measurement mode, and the lightness (L B * ) when measuring the chromaticity under a black background using the same test piece, the same measuring device, measurement mode, and light source. The difference between the two (ΔL * = (L W * ) - (L B *)) As the light transmittance (ΔL * (W - B)) (n = 3). The average values of the measured values are shown in Tables 1 to 3. When the light transmittance ΔL*(W - B) is 11 or more, it is evaluated as "○", when it is 8.6 or more and less than 11, it is evaluated as "Δ", and when it is less than 8.6, it is evaluated as "×".

[0155] <Method for Measuring Biaxial Bending Strength of Sintered Body>

[0156] Using the methods of the following Examples or Comparative Examples, sintered bodies with a diameter of 15 mm and a thickness of 1.2 mm were obtained. For the obtained sintered bodies, according to JIS T 6526:2012, using a universal precision testing machine Autograph (trade name "AG - I 100kN") manufactured by Shimadzu Corporation, the biaxial bending strength (n = 5) was measured at a crosshead speed of 0.5 mm / minute. When the biaxial bending strength is 840 MPa or more, it is evaluated as "○", and when it is less than 840 MPa, it is evaluated as "×".

[0157] <Examples 1 to 18, Comparative Examples 1 to 6, 12 and 13>

[0158] The prepared zirconia raw material and yttria raw material were weighed so as to be the mass % described in Table 1, and were put into water. Together with zirconia beads, they were put into a rotary container and pulverized by a ball mill to mix and pulverize the raw materials so that the particles contained in the slurry became the desired particle size. The particle size was measured as follows: Using a laser diffraction / scattering type particle size distribution measuring device (trade name "Partica LA - 950") manufactured by Horiba, Ltd., the slurry diluted with water was irradiated with ultrasonic waves for 30 minutes, and then, while being in contact with ultrasonic waves, the measurement was carried out based on the volume basis. The desired slurry was obtained with a ball mill treatment time of about 20 hours. For the slurries described in Examples 1 to 10 and Comparative Examples 1 to 3, the particle size distribution (volume basis) of the slurries measured by the aforementioned laser diffraction / scattering type particle size distribution measuring device is shown in Figure 4 . In Figure 4 , the vertical axis represents the value obtained by dividing each particle size by the total number, that is, the frequency (%). In Figure 4 , it was confirmed that: the slurries used in Comparative Examples 1 to 3 had small peaks on the large particle side and large particles around 1 μm. For Example 1, according to the measurement of the average particle size of the above powder and the measurement of the average particle size in the pre - sintered body, the surface was photographed using a scanning electron microscope, and for the obtained image, the average particle size was measured by image analysis to obtain the average particle size of the secondary aggregates of the powder and the average particle size of the secondary aggregates of the pre - sintered body. The results are shown in Figure 5A and Figure 6A . Figure 5A represents the particle size distribution (number basis) of the zirconia powder described in Example 1,Figure 6A Represents the particle size distribution (number basis) of the zirconia pre-sintered body.

[0159] Next, an organic binder was added to the obtained slurry and stirred using a rotating blade. The stirred slurry was dried and granulated using a spray dryer to obtain a powder. The average particle size of the powder was 40 μm. The powder was poured into a columnar mold and uniaxially pressed at a pressure of 33 MPa, and then further subjected to CIP treatment at 170 MPa to obtain a green body. The green body was placed in an electric furnace and heated from room temperature at a rate of 10 °C / min, held at 500 °C for 2 hours to degrease the organic components, held at 1000 °C for 2 hours, and slowly cooled at a rate of -0.4 °C / min to obtain a pre-sintered body. The obtained pre-sintered body was heated to the calcination temperature shown in Table 2 at a rate of 10 °C / min and held for 2 hours to obtain a sintered body.

[0160] As the zirconia and yttrium oxide raw materials, the following raw materials 1 to 6 were used.

[0161] Raw material 1: Zirconia was wet pulverized in water and then spray dried to obtain a dry powder. The monoclinic phase was 99% or more, the average primary particle size was 100 nm, and the BET specific surface area was 7.8 m 2 / g.

[0162] Raw material 2 was obtained by wet pulverization and classification of zirconia. In the wet pulverization, 2% by mass of polyacrylic acid was added and spray dried to obtain a dry powder. The monoclinic phase was 99% or more, the average primary particle size was 40 nm, and the BET specific surface area was 60 m 2 / g.

[0163] Raw material 3: Surface-modified nano zirconia was obtained by liquid-phase synthesis. Zirconium hydroxide obtained by hydrating zirconyl chloride was put into an aqueous nitric acid solution, exposed to ultrasonic waves, and dispersed until it became transparent. 3-phenylpropionic acid and 2% by mass of polyacrylic acid were added to the filtrate filtered through a filter, and the resulting precipitate was washed with water and dried to obtain a dry powder. The monoclinic phase was 99% or more, the average primary particle size was 15 nm, and the BET specific surface area was 90 m 2 / g.

[0164] Raw material 4: Yttrium oxide (Y2O3) was wet pulverized in water and then spray dried to obtain a dry powder. The average primary particle size was 200 nm, and the BET specific surface area was 6.5 m 2 / g.

[0165] Raw material 5 was commercially available NanoTek Y2O3 manufactured by CIK NanoTec Co., Ltd.; the average primary particle size was 15 nm, and the BET specific surface area was 32 m 2 / g.

[0166] <Comparative Examples 7 - 9>

[0167] The commercially available Zpex (registered trademark) (Raw material 6) manufactured by Tosoh Corporation was directly used for uniaxial pressure pressing, and the same operations as the method described above were performed to obtain a green compact, a pre-sintered body, and a sintered body.

[0168] The measurement results of each example and comparative example are shown in Tables 1 and 2. It should be noted that when converted to mol% based on the content (mass%) of yttrium oxide in Table 1, the content rate of yttrium oxide is 3.8 mol% relative to the total moles of zirconia and stabilizer in Examples 1 - 10, Comparative Examples 1 - 6, and 10 - 13. In addition, in Comparative Examples 7 - 9, the content rate of yttrium oxide is 3.1 mol% relative to the total moles of zirconia and stabilizer.

[0169]

[0170]

[0171] As shown in Table 2, in Comparative Examples 1 - 3 and 7 - 9 that contain only small particles and no large particles, the results show that the strength of the sintered body is low. In Comparative Examples 4 - 6 with a large average particle size of the secondary aggregates, the results show that the light transmittance of the sintered body is low. In both cases, it is impossible to achieve both high strength and high light transmittance. Furthermore, in Comparative Examples 10 - 13, the results show that the light transmittance of the sintered body is low, and in Comparative Example 11, the strength is also low. In both cases, it is impossible to achieve both high strength and high light transmittance. In contrast, it can be seen that in Examples 1 - 18, the light transmittance of the sintered body is 8.0 or more, and the biaxial flexural strength is 800 MPa or more, enabling both high strength and high light transmittance to be achieved.

Claims

1. A zirconia pre-sintered body, which comprises secondary aggregates with an average particle size of 275 nm or less, wherein the secondary aggregates are obtained by mixing powder (a1) with an average primary particle size of 100 nm or more and 200 nm or less and powder (a2) with an average primary particle size of 10 nm or more and less than 60 nm to prepare a mixture, and subjecting the mixture to a pulverization treatment, the secondary aggregates contain zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia, and the secondary aggregates contain large particles with an average primary particle size of 100 nm or more and 175 nm or less and small particles with an average primary particle size of 15 nm or more and less than 60 nm.

2. The zirconia pre-sintered body according to claim 1, wherein, In the secondary aggregates, the content of the large particles is 15 to 85% by volume, and the content of the small particles is 15 to 85% by volume.

3. The zirconia pre-sintered body according to claim 1 or 2, wherein, The stabilizer is yttria.

4. The zirconia pre-sintered body according to claim 1 or 2, wherein, The content of the stabilizer is 3.0 to 7.5 mol% based on the total moles of zirconia and the stabilizer, and at least a part of the stabilizer is not dissolved in zirconia.

5. The zirconia pre-sintered body according to claim 1 or 2, wherein, The density of the pre-sintered body is 2.75 g / cm 3 or more.

6. The zirconia pre-sintered body according to claim 1 or 2, wherein, The average crystal grain size of the crystal grains contained in the pre-sintered body, i.e., the sintered body calcined at a calcination temperature of 1,500 °C or less for 2 hours, is 0.70 μm or less.

7. The zirconia pre-sintered body according to claim 1 or 2, wherein, The density of the pre-sintered body, i.e., the sintered body calcined at a calcination temperature below 1,500 °C for 2 hours, is 5.8 g / cm 3 or more.

8. The zirconia pre-sintered body according to claim 1 or 2, wherein, In the particle size distribution based on the number measured using an image obtained by photographing the large particles and small particles with an electron microscope, there are two peaks. The particle size of the first peak representing the highest frequency particle size is 10 nm or more and less than 60 nm, and the particle size of the second peak is 60 nm or more and 200 nm or less.

9. A method for manufacturing a zirconia pre-sintered body, which is a method for manufacturing a zirconia pre-sintered body containing zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia, which uses powder (A) containing secondary aggregates, wherein the secondary aggregates are obtained by mixing powder (a1) with an average primary particle size of 100 nm or more and 200 nm or less and powder (a2) with an average primary particle size of 10 nm or more and less than 60 nm to prepare a mixture, and subjecting the mixture to a pulverization treatment, and the obtained average particle size is 275 nm or less, the secondary aggregates contain zirconia and a stabilizer capable of inhibiting the phase transformation of zirconia.

10. The manufacturing method of the zirconia pre-sintered body according to claim 9, wherein, Powder (A) containing the secondary aggregates contains 15 to 85% by mass of powder (a1) with an average primary particle size of 100 nm or more and 175 nm or less, and contains 15 to 85% by mass of powder (a2) with an average primary particle size of 15 nm or more and less than 60 nm.

11. The method for manufacturing a zirconia pre-sintered body according to claim 9 or 10, wherein, The stabilizer is powder (a1).

12. The method for manufacturing a zirconia pre-sintered body according to claim 9 or 10, wherein, The content of the stabilizer is 3.0 to 7.5 mol% based on the total moles of zirconia and the stabilizer, and at least a part of the stabilizer is not dissolved in zirconia.

13. The manufacturing method of the zirconia pre-sintered body according to claim 9 or 10, wherein, The stabilizer is yttria.

14. A method for manufacturing a powder, which is a method for manufacturing a powder for obtaining the zirconia pre-sintered body according to any one of claims 1 to 8, wherein, a slurry containing secondary aggregates is prepared, dried by spraying and granulated, The secondary aggregate is obtained by mixing a powder (a1) having an average primary particle diameter of 100 nm or more and 200 nm or less and a powder (a2) having an average primary particle diameter of 10 nm or more and less than 60 nm to prepare a mixture, and subjecting the mixture to a pulverization treatment, and the obtained average particle diameter is 275 nm or less.

15. A method for manufacturing a zirconia sintered body, wherein, The zirconia pre-sintered body according to any one of claims 1 to 8 is calcined.

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