Zirconia calcined body

Abstract

The present invention provides a pre-sintered body for obtaining a zirconia sintered body exhibiting both high strength and high translucency, and also provides a manufacturing method therefor. The present invention pertains to a zirconia pre-sintered body that contains secondary aggregates having an average particle size of at most 275 nm, wherein the secondary aggregates contain zirconia and a stabilizer capable of inhibiting the phase transition of zirconia, and are formed from large particles having an average primary particle size from 100-200 nm, inclusive, and small particles having an average primary particle size of at least 10 nm and less than 60 nm.

Description

[Technical Field]

[0001] This invention relates to a calcined body and a method for producing the same for obtaining a zirconia (zirconium(IV) oxide; ZrO2) sintered body that achieves both high strength and high light transmittance. [Background technology]

[0002] Ceramic sintering is generally a mass transfer phenomenon in which the free energy of the system decreases. When ceramic powder is solid-phase sintered, the primary particles contained in the powder grow in size, with their surface area or interface decreasing as the firing time increases, depending on their particle size and firing temperature. It is known that grain growth is more likely to occur when the particle size of the powder is small and the difference between it and the particle size of the target particle is large.

[0003] Furthermore, it is generally known that the fewer voids a ceramic sintered body contains, the higher its strength, and the smaller the particle size of the sintered body, the higher its strength. In addition, it is known that the fewer voids a ceramic sintered body contains, the higher its light transmittance, and the more particles it contains that are smaller than the wavelength of visible light, the higher its light transmittance.

[0004] Therefore, achieving both strength and transparency in ceramics requires that the sintered body be dense with few voids and that the particle size contained within the sintered body be kept small.

[0005] The voids between these ceramic particles coalesce as the grains grow, with some being expelled from the sintered body while others remain inside. In particular, rapid grain growth increases the amount of voids remaining inside the sintered body, making it challenging to obtain a high-density sintered body. Furthermore, when ceramics consist of polymorphs, density changes occur due to volume increases and decreases caused by temperature-dependent phase transformations, making void control a challenge.

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

[0007] Among them, when using a partially stabilized zirconia sintered body as a dental material, not only from the perspective of mechanical properties such as high strength and high toughness, but also from an aesthetic perspective, optical properties such as translucency and color tone are required. So far, in the partially stabilized zirconia sintered body, studies have been made on a zirconia sintered body having a high density and strength of the sintered body and translucency for the purpose of mimicking natural teeth. For example, the following Patent Documents 1 and 2 can be cited.

[0008] For example, Patent Document 1 discloses a translucent partially stabilized zirconia sintered body containing more than 4.0 mol% and not more than 6.5 mol% of yttria.

[0009] Further, Patent Document 2 discloses an agglomerate in which large particles (A) having a median diameter D50 of 0.2 to 12 μm and small particles (B) having a median diameter D50 of 0.01 to 0.3 μm have a maximum ratio of median diameters (A):(B) = 40:1 and a mixing ratio of (A):(B) = 0.01:99.9 to 99.9:0.01.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Disclosure of the Invention

Problems to be Solved by the Invention

[0011] However, in Patent Document 1, only small particles with a primary particle diameter of 32-38 nm were used for the raw material powder, and a secondary aggregate with an average particle diameter of 0.4 μm-0.5 μm was obtained. As a result, the density of the calcined body did not increase, and it was found that the light transmittance was insufficient. Furthermore, as in Patent Document 2, when the ratio of the median diameter of large particles (A) to small particles (B) is too large, the small particles (B) are immediately absorbed by the large particles (A) during firing. As a result, coarse particles originating from the large particles (A) remain before the voids are discharged, and a high-density sintered body cannot be obtained, resulting in a sintered body that is both high-strength and highly light-transmitting. Furthermore, it was found that when the proportion of small particles (B) with a median diameter D50 of less than 0.1 μm is between 100 and 85 parts by mass of powder, the small particles (B) fuse with the larger particles (A) of 0.2 to 12 μm. As a result, during granulation, the small particles (B) form hard aggregates or hard shells, preventing the acquisition of a high-density sintered body, and thus preventing the acquisition of a high-strength and highly translucent sintered body.

[0012] Therefore, the present invention aims to provide a calcined body for obtaining a zirconia sintered body that can achieve both high strength and high light transmittance, and a method for manufacturing the same. [Means for solving the problem]

[0013] The present inventors conducted extensive research to solve the above problems and found that a zirconia calcined body containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, which includes secondary aggregates with an average particle diameter of 275 nm or less, and in which these aggregates consist of particles with average particle diameters of 100 to 200 nm and 10 to 50 nm, can solve the above problems. Further investigations led to the completion of the present invention.

[0014] In other words, the present invention encompasses the following inventions. [1] Contains secondary aggregates with an average particle diameter of 275 nm or less, The secondary aggregate contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, A calcined zirconia body in which the secondary aggregate consists of large particles with an average primary particle diameter of 100 nm or more and 200 nm or less, and small particles with an average primary particle diameter of 10 nm or more and less than 60 nm. [2] The zirconia calcined body according to [1], wherein the secondary aggregate has a content of 15 to 85 volume% of large particles and a content of 15 to 85 volume% of small particles. [3] The zirconia calcined body according to [1] or [2], wherein the stabilizer is yttria. [4] The content of the stabilizer is 3.0 to 7.5 mol% relative to the total moles of zirconia and stabilizer, A calcined zirconia body according to any one of [1] to [3], wherein at least a portion of the stabilizer is not solid-dissolved in the zirconia. [5] The density of the calcined body is 2.75 g / cm³ 3 The above is a calcined zirconia body as described in any of [1] to [4]. [6] The calcined zirconia body according to any one of [1] to [5], wherein the average grain size of the crystal particles contained in the sintered body when fired at a firing temperature of 1,500°C or less for 2 hours is 0.70 μm or less. [7] The calcined body, when fired at a firing temperature of 1,500°C or less for 2 hours, has a density of 5.8 g / cm³. 3 The zirconia calcined body described in any of [1] to [6] above. [8] A zirconia calcined body according to any one of [1] to [7], wherein the particle size distribution based on the number of particles measured using images of the large and small particles taken with an electron microscope has two peaks, the first peak representing the most frequent particle size is in the particle size range of 10 nm or more and less than 60 nm, and the second peak is in the particle size range of 60 nm or more and 200 nm. [9] A method for producing a calcined zirconia body containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia, It contains powder (a1) with an average primary particle diameter of 100 nm or more and 200 nm or less, and powder (a2) with an average primary particle diameter of 10 nm or more and less than 60 nm. Using powder (A) containing secondary aggregates with an average particle size of 275 nm or less, A method for producing a calcined zirconia body, wherein the secondary aggregate comprises zirconia and a stabilizer capable of suppressing the phase transition of zirconia.

[10] The powder (A) containing the secondary aggregate is It contains 15-85% by mass of powder (a1) with an average primary particle size of 100 nm or more and 200 nm or less. A method for producing a calcined zirconia body according to [9], comprising 15 to 85% by mass of powder (a2) having an average primary particle diameter of 10 nm or more and less than 60 nm.

[11] The method for producing a calcined zirconia body according to [9] or

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

[12] The content of the stabilizer is 3.0 to 7.5 mol% relative to the total moles of zirconia and stabilizer, A method for producing a calcined zirconia body according to any one of [9] to

[11] , wherein at least a portion of the stabilizer is solid-dissolved in the zirconia.

[13] A method for producing a calcined zirconia body according to any one of [9] to

[12] , wherein the stabilizer is yttria. A method for producing powder for obtaining a calcined zirconia body as described in any of

[14] [1] to [8], It contains powder (a1) with an average primary particle diameter of 100 to 275 nm, and powder (a2) with an average primary particle diameter of 10 nm or more and less than 60 nm. A slurry containing secondary aggregates with an average particle size of 275 nm or less is manufactured. A method for producing powder by drying by spraying and then granulating. A method for producing a zirconia sintered body, comprising firing a zirconia calcined body described in any of

[15] [1] to [8]. [Effects of the Invention]

[0015] The calcined zirconia body of the present invention, when fired, can yield a sintered zirconia body that is suitable for dental materials, possessing both high strength and high translucency. Furthermore, the zirconia powder and zirconia-containing composition obtained by the powder production method of the present invention can suppress the occurrence of chipping (defects) in the zirconia molded body obtained when molded, thus exhibiting excellent shape retention. [Brief explanation of the drawing]

[0016] [Figure 1] This is a SEM image of a zirconia calcined body containing secondary aggregates according to Example 1. [Figure 2] This is an SEM image of the zirconia powder according to Example 1. [Figure 3] This is an SEM image of zirconia powder that formed a hard shell according to Comparative Example 4. [Figure 4] This shows the particle size distribution (by volume) of the zirconia slurries for Examples 1-10 and Comparative Examples 1-3. [Figure 5A] This shows the particle size distribution (based on the number of particles) in the zirconia powder according to Example 1. [Figure 5B] This shows the particle size distribution (based on particle count) in the zirconia powder related to Comparative Example 4. [Figure 6A] This shows the particle size distribution (based on the number of particles) in the calcined zirconia body according to Example 1. [Figure 6B] This shows the particle size distribution (based on particle count) in the zirconia calcined body according to Comparative Example 4. [Figure 7] This shows the particle size distribution (based on the number of particles) in the zirconia sintered body according to Example 1. [Modes for carrying out the invention]

[0017] The zirconia calcined body of the present invention comprises secondary aggregates having an average particle diameter of 275 nm or less, wherein the secondary aggregates contain zirconia and a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizer"), and the secondary aggregates consist of 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.

[0018] The present invention describes the zirconia calcined body. The zirconia calcined body can serve as a precursor (intermediate product) for a zirconia sintered body. In the present invention, the zirconia calcined body is a semi-sintered body in which zirconia particles (powder) have necked (solidified) and have been blocked in a state where they are not completely sintered.

[0019] The calcined zirconia body of the present invention contains secondary aggregates with an average particle diameter of 275 nm or less. The secondary aggregates contain primary particles, each consisting of large particles with an average particle diameter of 100 nm or more and 200 nm or less, and small particles with an average particle diameter of 10 nm or more and less than 60 nm, and are aggregated from these particles.

[0020] The average primary particle diameter of large particles affects the density of the sintered body, and is therefore preferably between 100 nm and 200 nm, more preferably between 104 nm and 175 nm, more preferably between 108 nm and 150 nm, and even more preferably between 110 nm and 135 nm. If the average primary particle diameter of large particles is less than 100 nm, aggregation with small particles may be strong, and a high-density sintered body may not be obtained. If the average primary particle diameter is greater than 200 nm, the light transmittance after sintering may decrease. Furthermore, the average primary particle diameter of small particles affects the average crystal grain size of the sintered body, and from the viewpoint of strength or light transmittance, it is preferably between 10 nm and 60 nm, more preferably between 15 nm and 50 nm, more preferably between 20 nm and 50 nm, and even more preferably between 25 nm and 50 nm. If the average primary particle diameter of small particles is less than 10 nm, there is a risk of reducing strength or light transmittance. If the average primary particle diameter is 60 nm or more, there is a risk of reducing light transmittance. Furthermore, the average particle diameter of the secondary aggregates is preferably 275 nm or less, more preferably 265 nm or less, more preferably 255 nm or less, and even more preferably 245 nm or less, from the viewpoint of shape retention of the molded body, density, light transmittance, and strength of the sintered body. Also, from the viewpoint of obtaining a high-density calcined body and sintered body, a form in which small particles are attached around large particles is preferred. For example, this form can be confirmed by visual inspection of electron microscope images. The average particle diameter and average primary particle diameter of the present invention can be calculated, for example, by image analysis of images taken with an electron microscope. The average primary particle diameter of the secondary aggregates, large particles, and small particles contained in the raw material powder, the molded body obtained by molding the raw material powder, and the calcined body thereof can be measured, for example, by the method described in the examples below.

[0021] In this invention, primary particles refer to the smallest bulk unit and include zirconia particles and stabilizer particles. Secondary aggregated particles are defined as aggregates of large particles with an average primary particle diameter of 100 nm or more and 200 nm or less, and small particles with an average primary particle diameter of 10 nm or more and less than 60 nm. The large particles contain zirconia and / or a stabilizer, and the small particles contain zirconia and / or a stabilizer, with at least one of the large or small particles containing a stabilizer. One preferred embodiment is a zirconia calcined body having secondary aggregated particles composed of zirconia particles, with the large particles containing zirconia particles and stabilizer particles (preferably yttria particles). Another preferred embodiment is a zirconia calcined body having secondary aggregated particles composed of zirconia particles, with the small particles containing zirconia particles and stabilizer particles (preferably yttria particles).

[0022] In the zirconia calcined body of the present invention, from the viewpoint of keeping the average crystal grain size of the sintered body small and increasing the light transmittance and strength of the sintered body, the content of large particles in the secondary aggregate is preferably 15 to 85 volume%, more preferably 18 to 83 volume%, and even more preferably 20 to 80 volume%. Furthermore, the zirconia calcined body of the present invention preferably contains 15 to 85 volume% of small particles, more preferably 17 to 82 volume%, and even more preferably 20 to 80 volume%. By being within these ranges, the average particle diameter of the secondary aggregate becomes 275 nm or less, the density of the calcined body increases, and the strength and light transmittance of the sintered body can be improved. The content of large and small particles in the present invention can be calculated, for example, by image analysis of images taken with an electron microscope.

[0023] The zirconia calcined material of the present invention contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia. The stabilizer is preferably capable of forming partially stabilized zirconia. Examples of the stabilizer include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y2O3), cerium oxide (CeO2), scandium oxide (Sc2O3), niobium oxide (Nb2O5), lanthanum oxide (La2O3), erbium oxide (Er2O3), and praseodymium oxide (Pr6O). 11 Examples of oxides include pr2O3, samarium oxide (Sm2O3), europium oxide (Eu2O3), and thulium oxide (Tm2O3), with yttria being preferred. The content of the stabilizer in the zirconia calcined body and its sintered body of the present invention can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence (XRF), etc.

[0024] In the zirconia calcined body and sintered body of the present invention, the content of the stabilizer (preferably yttria) is preferably 3.0 to 7.5 mol%, more preferably 3.5 to 7.0 mol%, and even more preferably 4.0 to 6.5 mol%, relative to the total moles of zirconia and stabilizer, from the viewpoint of the strength and light transmittance of the sintered body. If the yttria content is 3.0 mol% or more, the light transmittance of the sintered body can be increased, and if it is 7.5 mol% or less, the decrease in strength of the sintered body can be suppressed.

[0025] In the zirconia calcined body of the present invention, it is preferable that at least a part of the stabilizer is not dissolved in zirconia. That is, it is preferable that at least a part of the zirconia crystals exist in the monoclinic system. The fact that a part of the stabilizer is not dissolved in zirconia can be confirmed, for example, by an X-ray diffraction (XRD) pattern. When a peak derived from the stabilizer is confirmed in the XRD pattern of the zirconia calcined body, it means that there is a stabilizer that is not dissolved in zirconia in the zirconia calcined body. When the entire amount of the stabilizer is dissolved, basically, a peak derived from the stabilizer is not confirmed in the XRD pattern. However, depending on conditions such as the crystal state of the stabilizer, even when there is no peak of the stabilizer in the XRD pattern, the stabilizer may not be dissolved in zirconia. When the main crystal systems of zirconia are the tetragonal system and / or the cubic system and there is no peak of the stabilizer in the XRD pattern, it is considered that most, basically all, of the stabilizer is dissolved in zirconia. In the zirconia calcined body of the present invention, not all of the stabilizer needs to be dissolved in zirconia. In the present invention, the fact that the stabilizer is dissolved means, for example, that the element (atom) contained in the stabilizer is dissolved in zirconia.

[0026] In the zirconia calcined body of the present invention, the abundance ratio f of yttria not dissolved in zirconia (hereinafter sometimes referred to as "undissolved yttria") y can be calculated based on the following formula (1).

[0027] f y =I y / (I 28 +I 30 )*100 (1) In formula (1), I y represents the peak intensity of yttria near 2θ = 29° in the XRD pattern by CuKα rays. Also, I 28 represents the peak area near 2θ = 28° where the main peak of the monoclinic system appears, and I30 This represents the peak area around 2θ=30° where the main peak of the tetragonal or cubic crystal system appears.

[0028] Abundance of undissolved yttria f y The amount of undissolved yttria is preferably greater than 0%, more preferably 1% or more, even more preferably 2% or more, and particularly preferably 3% or more. y The upper limit depends on the yttria content in the calcined body. When the yttria content is 7.5 mol% or less relative to the total moles of zirconia and yttria, f y It can be 15% or less. For example, when the yttria content is 3.0 mol% or more and less than 4.5 mol%, f y It can be 7% or less. When the yttria content is 4.5 mol% or more and less than 5.5 mol%, f y It can be 10% or less. When the yttria content is 5.5 mol% or more and less than 6.5 mol%, f y It can be 11% or less. When the yttria content is 6.5 mol% or more and 7.5 mol% or less, f y This can be set to 15% or less.

[0029] When the yttria content is 3.0 mol% or more and less than 4.5 mol%, f y It is preferable that the content is 2% or more, more preferably 3% or more, even more preferably 4% or more, and particularly preferably 5% or more. When the yttria content is 4.5 mol% or more and less than 5.8 mol%, f y It is preferable that the content is 3% or more, more preferably 4% or more, even more preferably 5% or more, even more preferably 6% or more, and particularly preferably 7% or more. When the yttria content is 5.8 mol% or more and 7.5 mol% or less, f y It is preferable that the amount be 4% or more, more preferably 5% or more, even more preferably 6% or more, even more preferably 7% or more, and particularly preferably 8% or more.

[0030] Furthermore, in the zirconia calcined body of the present invention, tetragonal and cubic crystal peaks do not need to be substantially detected.

[0031] The density of the zirconia calcined body of the present invention is 2.75 g / cm³, from the viewpoint of increasing the strength and light transmittance of the sintered body. 3 The above is preferable, 2.85 g / cm³ 3 The above is more preferable, 2.95 g / cm³ 3 The above is even more preferable. The density of the zirconia calcined material is 2.75 g / cm³. 3 By meeting these conditions, the light transmittance of the zirconia sintered body can be 8.6 or higher, and the biaxial bending strength of the zirconia sintered body can be 850 MPa or higher. The light transmittance and biaxial bending strength of the zirconia sintered body can be measured by the method described in the examples below.

[0032] The zirconia calcined body of the present invention preferably has an average grain size of crystalline particles contained in the sintered body, when calcined at a calcination temperature of 1,500°C or lower for 2 hours, of 0.70 μm or less, more preferably 0.68 μm or less, and even more preferably 0.65 μm or less. By having an average particle size of 0.70 μm or less, the light transmittance of the zirconia sintered body can be 8.6 or higher, and the biaxial bending strength of the zirconia sintered body can be 850 MPa or higher. Furthermore, even when the average particle size is small, the density of the calcined body is 2.75 g / cm³. 3 If the value is less than this, the light transmittance will not improve, which is undesirable. Furthermore, for the zirconia calcined body of the present invention, the density of the sintered body when fired at a firing temperature of 1,500°C or less for 2 hours is 5.8 g / cm³. 3 It is preferable that the above conditions are met.

[0033] The zirconia calcined body of the present invention, as described in the examples below, is preferably one that has two peaks in the particle size distribution based on the number of particles measured using images of large and small primary particles captured by an electron microscope (e.g., SEM), in order to provide a zirconia sintered body that can achieve both high strength and high light transmittance, for example, when the average particle size is measured by image analysis of images taken by an electron microscope. In the present invention, a peak means a frequency of at least 5%, and from the standpoint of obtaining better strength and light transmittance, a frequency of 6% or more is preferred, 7% or more is more preferred, and 8% or more is even more preferred. Furthermore, in the particle size distribution based on the number of particles, it is preferable that the first peak, which represents the most frequent particle size (mode diameter), is located at a particle size of 10 nm or more and less than 60 nm, and the second peak is located at a particle size of 60 nm or more and 200 nm or less. More preferably, the first peak is located at an average particle size of 10 nm or more and 50 nm or less, and the frequency of the second peak is 8% or more, and even more preferably, the first peak is located at an average particle size of 10 nm or more and 50 nm or less, and the frequency of the second peak is 9% or more.

[0034] Next, we will describe the zirconia-containing composition for producing the zirconia calcined body of the present invention, and the powder used to produce the zirconia-containing composition.

[0035] The zirconia-containing composition serves as a precursor to the zirconia calcined body of the present invention described above. The content of zirconia and stabilizers in the zirconia-containing composition is calculated from the content of a predetermined zirconia calcined body, and the content is the same in the zirconia-containing composition and the zirconia calcined body. In the zirconia-containing composition, the content of the stabilizer can be measured using the same method as for the zirconia calcined body.

[0036] Zirconia-containing compositions include powder, fluids obtained by adding powder to a solvent, and molded bodies obtained by shaping powder into a predetermined form. When the zirconia-containing composition is in the form of powder, it may also be an aggregate of powder. Powder is formed by the aggregation of primary particles.

[0037] In this invention, primary particles refer to the smallest bulk units. For example, primary particles are spherical bodies that appear to be unbound and separable under an electron microscope (e.g., a scanning electron microscope). Primary particles include zirconia particles and stabilizing agent particles. Aggregates of primary particles are referred to as secondary particles.

[0038] In the present invention, the particles constituting the zirconia-containing composition preferably consist mainly of secondary aggregates (secondary aggregate particles). "Mainly" means that the content of secondary aggregates in the zirconia-containing composition should be 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The average particle diameter of the secondary aggregate particles is preferably 100 nm to 275 nm, more preferably 100 nm to 265 nm, even more preferably 100 nm to 255 nm, and particularly preferably 100 nm to 245 nm. When the average particle diameter is 100 nm or more, the increase in the adhesive strength of the secondary aggregate particles can be suppressed, and the secondary aggregate particles can be prevented from gathering together and consequently from becoming enlarged. If the average particle diameter of secondary aggregated particles exceeds 275 nm, the density of the molded body does not increase due to the skeleton effect (an effect in which particles come into contact with each other and support one another) during press molding, resulting in a decrease in strength and / or light transmittance after sintering, which is undesirable. The method for measuring the average particle diameter of secondary aggregated particles is as described in the examples below.

[0039] The particles constituting the secondary aggregated particles include large particles with an average primary particle diameter of 100 nm or more and 200 nm or less, and small particles with 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 even more preferably 110 nm or more and 135 nm or less. The method for measuring the average primary particle diameter of the large particles and small particles is as described in the examples below. If the average primary particle diameter of the large particles is less than 100 nm, aggregation with the small particles will be strong, forming a hard shell on the powder surface, and a high-density composition may not be obtained. If the average primary particle diameter of the large particles is greater than 200 nm, the sintering ability of the calcined body will be low, and unless the sintering temperature is raised to a high temperature, it may be difficult to increase the density after firing, and high light transmittance and high strength may not be obtained. 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 even more preferably 25 nm or more and 50 nm or less. If the average primary particle diameter of the small particles is less than 10 nm, a hard shell forms on the powder surface, preventing the acquisition of a high-density composition, which is undesirable. If the average particle diameter of the small particles is greater than 50 nm, the firing temperature cannot be lowered, which is also undesirable. Furthermore, for example, in visual confirmation of electron microscope images, a configuration in which small particles are attached around large particles is preferred. Moreover, in arranging small particles around large particles, it is preferable to control the surface potentials of the large and small particles to be in opposite signs so that they attract each other.

[0040] The average particle size of the secondary aggregate changes depending on the mixing ratio of large and small particles in the powder. Therefore, in the secondary aggregate, the particle content is preferably 15 to 85% by mass, more preferably 18 to 83% by mass, and even more preferably 20 to 80% by mass. If the large particle content is greater than 85% by mass, there is a risk that the adhesion of small particles to the large particles will be reduced, and if it is less than 15% by mass, the proportion of small particles will be too high, forming a hard shell on the powder surface, and a high-density composition may not be obtained.

[0041] In a zirconia-containing composition, 50% or more, preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more of the zirconia can be in the form of powder.

[0042] The bulk density of the zirconia-containing composition is 1.0 g / cm³. 3 Preferably, it is 1.1 g / cm³ or more. 3 It is more preferable that the amount be greater than or equal to 1.2 g / cm³. 3 It is even more preferable that the amount be greater than or equal to 1.3 g / cm³. 3 The above is particularly preferable. The bulk density of the lightly packed container can be measured in accordance with JIS R 9301-2-3.

[0043] The bulk density of the zirconia-containing composition is 1.3 g / cm³. 3 Preferably, it is 1.4 g / cm³ or more. 3 It is more preferable that the amount be greater than or equal to 1.5 g / cm³. 3 It is even more preferable that the above conditions are met. The bulk density of the heavy equipment can be measured in accordance with JIS R 9301-2-3.

[0044] The zirconia-containing composition may contain a binder.

[0045] Examples of the aforementioned binder include organic binders. Examples of organic binders include commonly used acrylic binders, acrylic acid binders, paraffinic binders, fatty acid binders, and polyvinyl alcohol binders. Among these organic binders, those having a carboxyl group in the molecular chain or carboxylic acid derivatives are preferred, acrylic binders (e.g., polyacrylic acid) are more preferred, and water-soluble polyacrylates are even more preferred. The polyacrylate may be a copolymer of acrylic acid or methacrylic acid with maleic acid, and may also contain sulfonic acid. Examples of salt cations include sodium and ammonium.

[0046] The binder content in the zirconia-containing composition is important because it adjusts the distance between primary particles in the zirconia-containing composition. The binder content is preferably 1.0 to 3.0% by mass, more preferably 1.2 to 2.8% by mass, and even more preferably 1.4 to 2.6% by mass in the overall zirconia-containing composition. If the binder content is less than 1.0% by mass in the overall zirconia-containing composition, chipping (defects) may occur in the molded article. If it is more than 3.0% by mass, the density of the molded article may not improve, and the strength and / or translucency of the sintered article may decrease.

[0047] The zirconia-containing composition may optionally contain additives such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (Al2O3), titanium dioxide (TiO2), silica (SiO2), dispersants (polyacrylic acid, 3-phenylpropionic acid, etc.), and defoamers. These components may be used individually or in combination of two or more. 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, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Er. 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 agents include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl. 10 O 17 Examples include the EU.

[0048] The aforementioned additive may be added during mixing or grinding, or after grinding.

[0049] One example of a method for producing a calcined zirconia body is to use a powder (A) containing a powder (a1) with an average primary particle diameter of 100 nm or more and 200 nm or less, and a powder (a2) with an average primary particle diameter of 10 nm or more and less than 60 nm, and a secondary aggregate with an average particle diameter of 275 nm or less, wherein the secondary aggregate contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia. First, the powder manufacturing process will be described.

[0050] There are no particular restrictions on the method for producing powder (A). For example, a breakdown process in which coarse particles are crushed to form fine particles, or a building-up process in which particles are synthesized from atoms or ions through nucleation and growth processes can be employed. As an example of a method for producing powder (A), one can produce a slurry containing powder (a1) with an average primary particle diameter of 100 nm or more and 200 nm or less, and powder (a2) with an average primary particle diameter of 10 nm or more and less than 60 nm, and containing secondary aggregates with an average particle diameter of 275 nm or less, and then spray-dry it to granulate and obtain powder (A). Powder (a1) may be zirconia powder, or stabilizer powder, or may contain both. Furthermore, if powder (a1) contains zirconia powder, it is preferable that powder (a2) contains stabilizer powder. If powder (a1) contains stabilizer powder, it is preferable that powder (a2) contains zirconia powder. Powder (a1) corresponds to the large particles. Powder (a2) corresponds to the small particles. The secondary aggregate comprises particles made of zirconia and a stabilizer capable of suppressing the phase transition of zirconia.

[0051] For example, first, a mixture is prepared by mixing zirconia and a stabilizer in a predetermined ratio (mixing step). A powder of a predetermined raw material compound is selected so that a powder (a1) with an average primary particle diameter of 100 nm or more and 200 nm or less, and a powder (a2) with an average primary particle diameter of 10 nm or more and less than 60 nm are obtained. If the stabilizer is yttria, the mixing ratio of zirconia and yttria can be such that it matches the aforementioned yttria content. The mixing of powder (a1) and powder (a2) may be done by dry mixing or wet mixing. The zirconia-containing composition can be pulverized so that the particles contained in the slurry have a desired particle size (for example, about 100 nm) (pulverization step). The mixing step and the pulverization step can be performed in the same step. Pulverization can be performed, for example, by dispersing the composition and binder in a solvent such as water (dispersion step), and then using a ball mill, bead mill, etc. to pulverize the composition. After the mixing step and / or grinding step, the mixture can be dried by spray drying using a spray dryer or the like to obtain the powder form described above (drying step). This makes it possible to produce the zirconia-containing composition in powder form (powder (A)) according to the present invention.

[0052] In the particle size distribution based on the number of particles measured using an image of powder (A) captured with an electron microscope, it is preferable that there are two peaks. In the present invention, the frequency of the peaks in powder (A) is at least 3%, and from the viewpoint of obtaining better intensity and light transmittance, it is preferable that it is 4% or more, more preferably 5% or more, and even more preferably 6% or more. Furthermore, in the particle size distribution based on the number of particles of powder (A), it is preferable that the first peak representing the most frequent particle size (mode diameter) is at a particle size of 10 nm or more and less than 60 nm, and the second peak is at a particle size of 60 nm or more and 200 nm or less. From the viewpoint of obtaining better intensity and light transmittance, it is preferable that the first peak is at an average particle size of 10 nm or more and the frequency of the second peak is 4% or more, and from the viewpoint of obtaining better intensity and light transmittance, it is preferable that the first peak is at an average particle size of 10 nm or more and the frequency of the second peak is 4% or more, and even more preferably that the first peak is at an average particle size of 10 nm or more and the second peak is 5% or more. Furthermore, in the particle size distribution of powder (A) based on the number of particles, the difference in frequency (%) between the first peak representing the most frequent particle size (mode diameter) and the second peak is preferably 20% or less, more preferably 18% or less, and even more preferably 15% or less. In addition, the difference in frequency (%) is preferably greater than 0%, more preferably 0.5% or more, and even more preferably 1.0% or more.

[0053] In the grinding process, it is preferable to use fine-sized grinding media, for example, grinding media of 100 μm or less. Furthermore, classification after grinding is preferable.

[0054] It is preferable to prepare zirconia and the stabilizer separately. For example, it is preferable that the zirconia preparation process (e.g., manufacturing process) and the stabilizer preparation process (e.g., manufacturing process) are independent and separate processes, rather than precipitating zirconia and the stabilizer simultaneously (in the same process). This makes it possible to suppress the solid solution of the stabilizer into the zirconia during the calcined body manufacturing process described later.

[0055] Powder (A) can be molded into a molded body by applying external force. The molding method is not limited to a specific method, and a suitable method can be selected as appropriate depending on the purpose. For example, it can be molded by press molding, injection molding, stereolithography, etc. Multi-stage molding may also be performed. For example, a zirconia-containing composition may be press-molded and then subjected to further CIP treatment.

[0056] The molded body may have a disc shape, a rectangular parallelepiped shape, or a dental product shape (e.g., a tooth crown shape).

[0057] For example, the molded body may be a columnar shape obtained by filling a mold with zirconia powder (the powder (A) containing zirconia and a stabilizer capable of suppressing the phase transition of zirconia) and compressing it with a uniaxial pressure press. The higher the surface pressure during press molding, the higher the density of the molded body. On the other hand, if the density of the molded body is too high, the zirconia calcined body becomes hard. Therefore, the surface pressure during press molding is preferably 30 to 200 MPa. When the surface pressure of the press is 30 MPa or higher, the molded body has excellent shape retention, and when it is 200 MPa or lower, the density of the molded body does not increase too much, making it easier to prevent it from becoming hard.

[0058] The aforementioned molded articles also include molded articles that have been densified by high-temperature and high-pressure treatments such as CIP (Cold Isostatic Pressing). From the same viewpoint as above, the water pressure is preferably 30 to 200 MPa.

[0059] The zirconia calcined body of the present invention serves as a precursor (intermediate product) for sintered zirconia bodies. Calcined bodies also include those that have been molded. The zirconia calcined body of the present invention also includes, for example, dental products (e.g., prostheses in the shape of tooth crowns) that have been processed using a CAD / CAM (Computer-Aided Design / Computer-Aided Manufacturing) system from a calcined zirconia disc.

[0060] The content of zirconia and stabilizer in the zirconia calcined body of the present invention is the same as the content in the zirconia-containing composition or molded body before the production of the zirconia calcined body. From the viewpoint of strength and light transmittance of the sintered body produced from the zirconia calcined body of the present invention, yttria is preferred as the stabilizer. The molded body is produced by molding (for example, press molding) a zirconia-containing composition, and the content of zirconia and stabilizer can be considered the same as that of the zirconia-containing composition.

[0061] The proportion of undissolved stabilizer in the calcined zirconia body of the present invention is, as described above, the proportion of undissolved yttria f y It is calculated and depends on the calcination temperature.

[0062] In the method for producing a zirconia calcined body of the present invention, the calcination temperature is preferably 830 to 1080°C, more preferably 850 to 1050°C, and even more preferably 895 to 1000°C. If the calcination temperature is below 830°C, the strength and hardness of the calcined body may be insufficient, and the machinability may decrease. If the calcination temperature is greater than 1080°C, the strength and hardness of the calcined body may increase, which may decrease the machinability, and depending on the content of the stabilizer, the amount of stabilizer in the solid solution may increase, and a phase that undergoes a phase transition to a tetragonal and / or cubic crystal system due to heat may be generated.

[0063] Holding the calcined material at the maximum calcination temperature for a certain period of time is preferable because it can result in a hardness within a desirable range and improved machinability. The calcination conditions depend on the density of the calcined material, the average particle size of the calcined material, and the amount of binder, but it is preferable to hold it at the maximum calcination temperature for 30 minutes to 6 hours. Furthermore, it is preferable that the heating rate and cooling rate be 300°C / min or less.

[0064] The zirconia calcined body of the present invention can be machined to produce a machined body. The machining method is not limited to a specific method, and a suitable method can be selected as appropriate depending on the purpose. For example, a zirconia disc, which is also a calcined body, can be machined into the shape of a dental product (e.g., a prosthesis in the shape of a tooth crown) using a CAD / CAM system to produce a machined body.

[0065] The machined body may have its surface smoothness improved using tools such as abrasives (for example, Pearl Surface®, manufactured by Kuraray Noritake Dental Co., Ltd.).

[0066] A zirconia sintered body (hereinafter sometimes simply referred to as "zirconia sintered body" or "sintered body") can be produced by subjecting the calcined zirconia body of the present invention, or a machined body thereof, to a sintering process in which it is fired at a temperature at which zirconia particles sinter. From the viewpoint of controlling grain growth and obtaining a sintered body with high light transmittance and high strength, the firing temperature is preferably, for example, 1300 to 1600°C, more preferably 1350 to 1550°C, and even more preferably 1350 to 1450°C. Within the above range, the average grain size of the crystalline particles contained in the sintered body is 0.7 μm or less, and the density of the sintered body is 5.8 g / cm³. 3 This process results in high light transmittance and high strength.

[0067] In the sintering process, the holding time at the sintering temperature (e.g., the maximum firing temperature) is preferably less than 120 minutes, more preferably 90 minutes or less, even more preferably 75 minutes or less, even more preferably 60 minutes or less, particularly preferably 45 minutes or less, and most preferably 30 minutes or less. The holding time is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more.

[0068] The zirconia calcined body of the present invention allows for a reduction in the firing time required to produce a sintered zirconia body without reducing its translucency or strength. In particular, it allows for a reduction in the holding time at the maximum firing temperature required to produce the sintered body (short-time sintering). This increases production efficiency, and when the zirconia calcined body of the present invention is applied to dental products, it reduces the time required from determining the dimensions of the dental product to be used for treatment, machining it, and making it ready for treatment, thereby reducing the time burden on the patient. Furthermore, it can reduce energy costs.

[0069] In the sintering process, the holding time at the sintering temperature (e.g., the maximum firing temperature) can be, for example, 25 minutes or less, 20 minutes or less, or 15 minutes or less.

[0070] In the sintering process, the heating rate and cooling rate should preferably be set to minimize the time required for the sintering process. For example, the heating rate can be set to reach the maximum firing temperature in the shortest possible time, depending on the performance of the firing furnace. The heating rate to the maximum 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, or 200°C / min or more. The cooling rate should preferably be set to a rate that prevents defects such as cracks from occurring in the sintered body. For example, after heating is complete, the sintered body can be allowed to cool at room temperature.

[0071] This invention describes a zirconia sintered body obtained by sintering a calcined zirconia body or a machined body thereof. A zirconia sintered body can be defined as, for example, a body in which zirconia particles have reached a sintered state. The relative density of the zirconia sintered body is preferably 99.5% or higher. The relative density can be calculated as the ratio of the measured density measured by the Archimedes method to the theoretical density. The relative density refers to the value obtained by dividing the density d1 of a sintered body obtained by firing a molded body at a high temperature in a molded body in which powder is filled into a specific mold and shaped into a specific shape by pressure, by the theoretical zirconia density d2 (which does not include internal voids).

[0072] Zirconia sintered bodies include not only sintered bodies produced by sintering molded zirconia particles under normal or non-pressurized conditions, but also sintered bodies that have been densified by high-temperature and high-pressure treatments such as HIP (Hot Isostatic Pressing).

[0073] The density of a zirconia sintered body is such that higher density results in fewer internal voids and less light scattering, thus improving light transmission. Therefore, 5.80 g / cm³ is considered ideal. 3 Preferably, it is 5.82 g / cm³ or more. 3It is more preferable that the amount be greater than or equal to 5.87 g / cm³. 3 It is even more preferable that the above conditions are met. It is particularly preferable that the zirconia sintered body contains substantially no voids.

[0074] The average grain size of the crystalline particles contained in the zirconia sintered body is preferable because the higher the proportion of particles smaller than the wavelength of visible light, the higher the light transmittance and strength. The preferred range is 0.70 μm or less, more preferably 0.68 μm or less, and even more preferably 0.65 μm or less. The average grain size of the crystalline particles contained in the zirconia sintered body can be measured by the method described in the examples below.

[0075] The content ratio of zirconia and stabilizers in the zirconia sintered body is the same as that of the composition before the sintering and / or calcined body. Regarding the crystal system of zirconia in the sintered body, the proportion of monoclinic crystals is preferably 10% or less, more preferably 5% or less, and even more preferably substantially absent (can be considered as 0%). Crystal systems other than monoclinic are tetragonal and / or cubic.

[0076] Regarding the solid solution ratio of the stabilizer in the zirconia sintered body, it is preferable that 95% or more of the contained stabilizer is solid-dissolved in the zirconia, and it is more preferable that substantially all of the stabilizer is solid-dissolved. The presence of undissolved yttria f y The amount is preferably 5% or less, more preferably 1% or less, and even more preferably substantially all (0%) is in solid solution.

[0077] The strength of the zirconia sintered body is preferable to be as high as possible. For example, a biaxial bending strength of 800 MPa or higher is preferable, 820 MPa or higher is more preferable, and 840 MPa or higher is even preferable. The biaxial bending strength can be measured in accordance with ISO 6872:2015, for example, by the method described in the examples below.

[0078] The light transmittance of the zirconia sintered body is preferably 8.6 or higher, more preferably 10 or higher, and even more preferably 11 or higher. Here, light transmittance refers to the L* value of lightness (color space) in the L*a*b* color system (JIS Z 8781-4:2013), where the L* value measured against a white background of a 1.2 mm thick sample is taken as the first L* value, and the L* value measured against a black background of the same sample is taken as the second L* value, and the second L* value is obtained by subtracting the second L* value from the first L* value. Regarding the method of preparing the sample, first, a disc-shaped molded body with a diameter of 19 mm can be produced by press molding of the powder (composition) so that the thickness of the sintered body is 1.2 mm, followed by CIP molding. Next, the molded body can be fired under predetermined firing conditions to produce a sintered body with a thickness of 1.2 mm that will serve as the sample. For measuring the L* value, after applying a contact solution to the surface of the sample, the L* values ​​can be measured against a black and white background using a colorimeter (for example, the dental colorimeter "Crystal Eye CE100-DC / JP" and the analysis software "Crystal Eye" (manufactured by Olympus Corporation)). As the contact solution, for example, one with a refractive index nD of 1.60 measured at a measurement wavelength of 589 nm (sodium D line) can be used.

[0079] The zirconia sintered body may be a molded body having a predetermined shape. For example, the sintered body may have a disc shape, a rectangular parallelepiped shape, or a dental product shape (e.g., a tooth crown shape).

[0080] The methods for producing the compositions, powders, molded articles, calcined articles, machined articles, and sintered articles described herein are not limited to those described above, and various known methods can be applied as long as the desired configuration and effects of the present invention are obtained.

[0081] The calcined body of the present invention can be suitably used in zirconia processed products where strength and / or aesthetics are required after firing, such as dental materials, fiber optic cable connectors, smartphone casings, etc. [Examples]

[0082] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited in any way by these examples.

[0083] <Measurement of average particle size of powder> The powders obtained in the following examples and comparative examples were impregnated in a two-component curable epoxy resin (product name "MA2+", manufactured by Meiwa Forsis Co., Ltd.) under vacuum and embedded for 12 hours. The resulting cured material was polished with sandpaper to expose the powder cross-section. Surface imaging (SEM image) was obtained using an ultra-high-resolution analytical scanning electron microscope (product name "SU-70", manufactured by Hitachi, Ltd.). The average particle diameter was calculated from the obtained image by image analysis and defined as the "average particle diameter of the secondary aggregate of the powder". Image analysis software "Image-Pro Plus" manufactured by Hakuto Co., Ltd. was used to measure the average particle diameter. The captured SEM image was binarized, the grain boundaries of each crystal particle were added to the resulting image, and then the particles were recognized from the field of view (region). The particle diameter obtained with Image-Pro Plus is the diameter passing through the center of gravity of the particle, and the average particle diameter is the average of the lengths of line segments connecting the outlines passing through the center of gravity, which are determined from the outline of the particle, measured at 2-degree intervals with the center of gravity as the center. For each example and comparative example, the average value of 10 fields of view was used as the average particle diameter of the powder. Furthermore, regarding the primary particle diameter of particles in secondary aggregates, since the particle diameter distribution based on the number of particles in this invention has two peaks, the average particle diameters were determined by peak separation and used as the "average particle diameters" for large and small particles. Peak separation was performed by fitting two peaks to the particle size distribution data obtained from image analysis using Gaussian and Lorentz functions, and calculating the average particle diameter of each single peak. For peak separation, for example, the "Peak Separation" file at the link below can also be used. https: / / www.jie.or.jp / publics / index / 497 / Figure 5A shows the particle size distribution (based on the number of particles) of the powder according to Example 1, and Figure 5B shows the particle size distribution (based on the number of particles) of the powder according to Comparative Example 4. The vertical axis represents frequency (%), and the horizontal axis represents particle size (nm).

[0084] <Measurement of median diameter D50 of particles in slurry> The median diameter D50 was determined using a laser diffraction / scattering particle size distribution analyzer (product name "Partica LA-950") manufactured by Horiba, Ltd. A slurry diluted with water was subjected to ultrasonic irradiation for 30 minutes, and then measured by volume while applying ultrasonic waves. The particle size at which the cumulative frequency of the obtained measurement results reached 50% was calculated using software and defined as the median diameter D50.

[0085] <Method for evaluating the shape retention of molded products> The powder obtained in the following examples or comparative examples was filled into a columnar mold, and the mold was clamped from above and below. Uniaxial pressing was performed until a stress of 33 MPa was reached. After pressing, the molded body was visually inspected to see if any corners of the rectangle were chipped (n=5). If two or more out of five had chips (defects) of 0.7 mm or more, it was evaluated as having poor shape retention and marked with "×", while those without chips were evaluated as having excellent shape retention and marked with "○".

[0086] <Measurement of average particle size in calcined body> Using the calcined bodies obtained in the following examples or comparative examples, surface images were obtained using a scanning electron microscope (product name "VE-9800", manufactured by Keyence Corporation). The average particle diameter was measured from the obtained images by image analysis and defined as the "average particle diameter of the secondary aggregates of the calcined body". Image analysis software "Image-Pro Plus" manufactured by Hakuto Co., Ltd. was used to measure the average particle diameter. The particle diameter obtained with Image-Pro Plus is the diameter passing through the center of gravity of the particle, and the average particle diameter is the average of the lengths of line segments connecting the outlines passing through the center of gravity, which are determined from the outline of the particle, measured at 2-degree intervals with the center of gravity as the center. For one sample in each example and comparative example, the average value of 10 fields of view was taken as the average particle diameter of the calcined body. Furthermore, regarding the primary particle diameter of the particles in the secondary aggregates, in this invention, since the particle diameter distribution has two peak tops, the peaks were separated and the average particle diameters for each were determined and defined as the "average particle diameter" for large particles and small particles. Figure 1 shows the scanning electron microscope image of the zirconia calcined body according to Example 1. Furthermore, the particle size distribution (based on the number of particles) of the zirconia calcined material according to Example 1 is shown in Figure 6A, and the particle size distribution (based on the number of particles) of the zirconia calcined material according to 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 calcined material.

[0087] <Method for determining whether zirconia and stabilizers are not partially solid-solved in a zirconia calcined material> To determine whether at least a portion of the stabilizer is not solid-dissolved in the zirconia calcined body of the present invention, a zirconia calcined body was manufactured as a 2 mm thick plate. The plate was measured using a fully automated horizontal multi-purpose X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and integrated X-ray analysis software (SmartLab Studio II, manufactured by Rigaku Corporation) under the following conditions, and the presence or absence of a peak around 29° was checked. The presence or absence of a peak was determined by setting the peak with the highest intensity to 100 in the range of 2θ = 10 to 90°. If the stabilizer peak was 1 or higher, it was determined to be present without solid-dissolved, and marked as "○". If it was less than 1, it was determined to be solid-dissolved and not present as a standalone stabilizer, and marked as "×". X-ray source: Cu Kα (λ=1.54186Å) Goniometer length: 300mm Optical system: Concentration method Detector: High-speed 1D X-ray detector (D / teX Ultra250) Monochromatization: Kβ filter Tube voltage: 40kV Tube current: 30mA Scan axis: 2θ / θ Scan speed: 0.2° / min Sampling step: 0.01°

[0088] <Method for measuring the content [volume %] of primary particles in secondary aggregates in calcined materials> The volume of each individual particle was calculated from the particle size obtained using Image-Pro Plus. Because the particle size distribution had two peaks, the peaks were separated and their respective volume percentages were determined.

[0089] <Method for measuring the density of a partially burned body> The calcined bodies obtained in the following examples or comparative examples were fabricated in the shape of a rectangular parallelepiped with a base of 14 mm × 14 mm, and their volume was determined using a micrometer and a precision balance as (mass of calcined body) / (volume of calcined body) (average value for n=3).

[0090] <Method for measuring the average grain size in a sintered body> In the sintered bodies obtained in the following examples or comparative examples, surface images were obtained using a scanning electron microscope (product name "VE-9800", manufactured by Keyence Corporation). The average grain size was calculated from the obtained images by image analysis. Image-Pro Plus, image analysis software manufactured by Hakuto Co., Ltd., was used to measure the average grain size. The captured SEM images were binarized, the brightness range was adjusted so that grain boundaries were clear, and particles were recognized from the field of view (region). The grain size obtained with Image-Pro Plus is the diameter passing through the centroid of the crystal grain, and the average grain size is the average of the length of the line segment connecting the outer edges passing through the centroid, determined from the outer edges of the particles, measured at 2-degree intervals centered on the centroid. For one sample in each example and comparative example, the average value of 10 fields of view was taken as the average grain size in the sintered body. Figure 7 shows the measurement results of the particle size distribution (number basis) of the average grain size in the zirconia sintered body according to Example 1. In Figure 7, the vertical axis represents the number, and the horizontal axis represents the diameter (μm).

[0091] <Method for measuring the density of a sintered body> For the columnar sintered bodies obtained in the following examples or comparative examples, the dimensions were accurately measured using a micrometer, and the mass was measured using a precision balance. The density was then calculated using the formula (mass of sintered body) / (volume of sintered body) (average value for n=3). The density of the sintered body was 5.80 g / cm³. 3 The above is marked with "○", 5.80g / cm³ 3 Values ​​less than a certain value were evaluated as "×".

[0092] <Evaluation of light transmittance of sintered bodies> The sintered body obtained in the following examples or comparative examples was polished into a 1.2 mm thick flat plate sample, and the chromaticity was measured using a spectrophotometer manufactured by Olympus Corporation (product name "Crystal Eye") in 7-band LED light source mode against a white background, and the brightness (L) was measured. W * ) and the brightness (L) when measuring chromaticity on a black background using the same test specimen, the same measuring device, measurement mode, and light source. B * ) is measured, and the difference between the two (ΔL * =(L W * )-(LB * )) Translucency (ΔL * (WB) was used (n=3). The average values ​​of the measured values ​​are shown in Tables 1-3. Transmittance ΔL*(WB) was evaluated as follows: 11 or higher was marked "○", 8.6 or higher and less than 11 was marked "△", and less than 8.6 was marked "×".

[0093] <Method for measuring the biaxial bending strength of a sintered body> A sintered body with a diameter of 15 mm and a thickness of 1.2 mm was obtained using the method described in the following examples or comparative examples. The biaxial bending strength of the obtained sintered body was measured in accordance with JIS T 6526:2012 using a Shimadzu Corporation Autograph universal precision testing machine (product name "AG-I 100kN") at a crosshead speed of 0.5 mm / min (n=5). The biaxial bending strength was evaluated as "○" for 840 MPa or higher and "×" for less than 840 MPa.

[0094] <Examples 1-18, Comparative Examples 1-6, 12, and 13> The separately prepared zirconia and yttria raw materials were weighed to the mass percentages listed in Table 1 and added to water. This, along with zirconia beads, was placed in a rotary container, and the raw materials were mixed and ground by ball milling to obtain the desired particle size in the slurry. The particle size was measured using a laser diffraction / scattering particle size distribution analyzer (product name "Partica LA-950") manufactured by Horiba, Ltd., by irradiating the slurry diluted with water with ultrasound for 30 minutes, and then measuring it on a volume basis while applying ultrasound. The desired slurry was obtained after a ball milling time of approximately 20 hours. Figure 4 shows the particle size distribution (volume basis) of the slurries for Examples 1 to 10 and Comparative Examples 1 to 3, as measured by the laser diffraction / scattering particle size distribution analyzer. In Figure 4, the vertical axis shows the frequency (%), which is the value obtained by dividing each particle size by the total number of particles. In Figure 4, it was confirmed that the slurries used in Comparative Examples 1 to 3 had a small peak on the large particle side, with large particles around 1 μm. For Example 1, following the measurements of the average particle size of the powder and the calcined body described above, surface images were obtained using a scanning electron microscope. The average particle size was then measured from the obtained images using image analysis to obtain the average particle size of the secondary aggregates of the powder and the secondary aggregates of the calcined body. The results are shown in Figures 5A and 6A. Figure 5A shows the particle size distribution (number basis) of the zirconia powder related to Example 1, and Figure 6A shows the particle size distribution (number basis) of the zirconia calcined body.

[0095] Next, an organic binder was added to the obtained slurry and stirred with a rotary impeller. 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. This powder was poured into a columnar mold, uniaxially pressed at a pressure of 33 MPa, and then further subjected to CIP treatment at 170 MPa to obtain a molded body. The molded body was placed in an electric furnace, heated from room temperature at 10°C / min, and held at 500°C for 2 hours to degrease the organic components, then held at 1000°C for 2 hours, and slowly cooled at -0.4°C / min to obtain a calcined body. The obtained calcined body was heated at 10°C / min to the firing temperature listed in Table 2 and held for 2 hours to obtain a sintered body.

[0096] The following raw materials 1-6 were used as zirconia and yttria raw materials.

[0097] Raw material 1 was obtained by wet grinding zirconia in water and then spray drying to obtain a dry powder. It was monoclinic with a composition of 99% or more, an average primary particle size of 100 nm, and a BET specific surface area of ​​7.8 m². 2 It was / g.

[0098] Raw material 2 was obtained by wet grinding and classification of zirconia. During wet grinding, 2% by mass of polyacrylic acid was added, and the mixture was spray-dried to obtain a dry powder. It was monoclinic with a composition of 99% or more, an average primary particle size of 40 nm, and a BET specific surface area of ​​60 m². 2 It was / g.

[0099] For raw material 3, surface-modified nanozirconia was obtained by liquid-phase synthesis. Zirconium hydroxide, obtained by hydrating zirconium oxychloride, was placed in an aqueous nitric acid solution and dispersed under ultrasonic waves until transparent. 2% by mass of 3-phenylpropionic acid and polyacrylic acid were added to the filtered filtrate, and the resulting precipitate was washed with water and dried to obtain a dry powder. The resulting powder was monoclinic (over 99%), had an average primary particle size of 15 nm, and a BET specific surface area of ​​90 m². 2 It was / g.

[0100] Raw material 4 was obtained by wet grinding yttria (Y2O3) in water, followed by spray drying to obtain a dry powder. The average primary particle size was 200 nm, and the BET specific surface area was 6.5 m². 2 It was / g.

[0101] Raw material 5 was commercially available NanoTek Y2O3 from CIK Nanotek Co., Ltd. The average primary particle size was 15 nm, and the BET specific surface area was 32 m². 2 It was / g.

[0102] <Comparative Examples 7-9> Molded bodies, calcined bodies, and sintered bodies were obtained in the same manner as described above, except that commercially available Zpex® (registered trademark) (raw material 6) manufactured by Tosoh Corporation was directly used in a uniaxial pressure press.

[0103] The measurement results for each example and comparative example are shown in Tables 1 and 2. Converting the yttria content (mass%) in Table 1 to mol%, the yttria content was 3.8 mol% relative to the total moles of zirconia and stabilizer in Examples 1-10, Comparative Examples 1-6, and 10-13. In Comparative Examples 7-9, the yttria content was 3.1 mol% relative to the total moles of zirconia and stabilizer.

[0104] [Table 1]

[0105] [Table 2]

[0106] As shown in Table 2, Comparative Examples 1-3 and 7-9, which contained only small particles and no large particles, had low strength in the sintered bodies, and Comparative Examples 4-6, which had a large average particle size in the secondary aggregates, had low light transmittance in the sintered bodies. In all cases, high strength and high light transmittance could not be achieved simultaneously. Furthermore, Comparative Examples 10-13 had low light transmittance in the sintered bodies, and Comparative Example 11 also had low strength. In all cases, high strength and high light transmittance could not be achieved simultaneously. In contrast, in Examples 1-18, the light transmittance of the sintered bodies was 8.0 or higher, and the biaxial bending strength was 800 MPa or higher, indicating that high strength and high light transmittance could be achieved simultaneously.

Claims

1. It contains secondary aggregates with an average particle diameter of 100 nm or more and 275 nm or less. The secondary aggregate contains zirconia and yttria, and The secondary aggregate consists of large particles with an average primary particle diameter of 100 nm or more and 200 nm or less, and small particles with an average primary particle diameter of 10 nm or more and less than 60 nm. The yttria content is 3.0 to 7.5 mol% relative to the total mol of zirconia and yttria. In the particle size distribution based on the number of particles, measured using images of the large and small particles captured with an electron microscope, the distribution includes two peaks based on the large and small particles, A calcined zirconia body in which the secondary aggregate has a content of large particles of 15 to 85 volume percent and a content of small particles of 15 to 85 volume percent.

2. The calcined zirconia body according to claim 1, wherein at least a portion of the yttria is not solid-dissolved in the zirconia.

3. The density of the aforementioned calcined material is 2.75 g / cm³. 3 The zirconia calcined body according to claim 1 or 2.

4. The calcined zirconia body according to any one of claims 1 to 3, wherein the average grain size of the crystal particles contained in the sintered body after firing at a firing temperature of 1,350°C or higher and 1,500°C or lower for 2 hours is 0.70 μm or less.

5. The aforementioned calcined body, when fired at a firing temperature of 1,350°C to 1,500°C for 2 hours, has a sintered body density of 5.8 g / cm³. 3 The zirconia calcined body according to any one of claims 1 to 4.

6. A calcined zirconia body according to any one of claims 1 to 5, wherein the first peak representing the most frequent particle size is located at a particle size of 10 nm or more and less than 60 nm, and the second peak is located at a particle size of 60 nm or more and 200 nm.

7. A method for producing a calcined zirconia body containing zirconia and yttria, A step of forming a molded body by molding a powder (A) containing a powder (a1) with an average primary particle diameter of 100 nm or more and 200 nm or less, and a powder (a2) with an average primary particle diameter of 10 nm or more and less than 60 nm, and a secondary aggregate with an average particle diameter of 100 nm or more and 275 nm or less, A step of producing a calcined body by calcining the molded body at a calcination temperature of 830 to 1080°C, Includes, The secondary aggregate comprises zirconia and yttria, The yttria content is 3.0 to 7.5 mol% relative to the total mol of zirconia and yttria. In the particle size distribution based on the number of particles measured using an image of the powder (A) captured with an electron microscope, two peaks based on the powder (a1) and the powder (a2) are included. A method for producing a calcined zirconia body, wherein the powder (A) containing the secondary aggregate contains 15 to 85% by mass of the powder (a1) and 15 to 85% by mass of the powder (a2).

8. The method for producing a calcined zirconia body according to claim 7, wherein yttria is the powder (a1).

9. A method for producing a calcined zirconia body according to claim 7 or 8, wherein at least a portion of the yttria is not solid-dissolved in the zirconia.

10. A method for producing powder for obtaining a calcined zirconia body according to any one of claims 1 to 6, It contains a powder (a1) with an average primary particle diameter of 100 to 275 nm, and a powder (a2) with an average primary particle diameter of 10 nm or more and less than 60 nm. A slurry containing secondary aggregates with an average particle size of 100 nm to 275 nm is manufactured. A method for producing powder by drying by spraying and then granulating.

11. A method for producing a zirconia sintered body, comprising firing a zirconia calcined body according to any one of claims 1 to 6.

Images