Zirconia calcined body with good machinability

Abstract

The present invention provides a zirconia calcined body having exceptional machinability and a low probability of support fracture or chipping during cutting, and a method for producing the zirconia calcined body. The present invention relates to a zirconia calcined body that contains zirconia and a stabilizer capable of suppressing phase transition of zirconia, the stabilizer content being 3-8 mol% relative to the total mol of zirconia and stabilizer, at least some of the stabilizer not forming a solid solution with zirconia, and the Vickers hardness measured in accordance with JIS Z 2244:2009 being 65-135 HV 5 / 30.

Description

[Technical Field]

[0001] The present invention relates to a zirconia calcined body having good machinability and a method for producing the same. [Background technology]

[0002] Zirconia can undergo phase transition between multiple crystalline phases with the aid of stabilizers, and as such has high mechanical strength and translucency, making it suitable for use as a dental material. However, zirconia sintered bodies made by sintering zirconia particles (powder) have high strength and toughness, making them difficult to machine directly into the desired shape.

[0003] Therefore, a common procedure is to mold zirconia powder into a compact such as a disk or rectangular parallelepiped, and then sinter (hereinafter referred to as "calcination") the compact in a temperature range below sintering, and then cut the resulting calcined disk or other compact into a machined body with a desired shape, such as a shape resembling a tooth or a part of a tooth. By firing this machined body at a temperature equal to or higher than the sintering temperature, a zirconia sintered body having the desired shape can be obtained.

[0004] The obtained zirconia sintered body is generally subjected to a polishing operation to obtain surface smoothness from an aesthetic viewpoint. However, if chipping occurs during the cutting process of the calcined body and the surface smoothness is low even before sintering, polishing after sintering requires a great deal of effort. Therefore, from the viewpoint of industrial productivity, a zirconia calcined body with a low risk of chipping during the cutting process is desired.

[0005] Furthermore, when cutting a machined body having a desired shape, such as a tooth, from a zirconia calcined body, supports (also called "supports" or "sprue") are also produced to connect the machined body to the calcined body. These supports are separated from the machined body using a tool or the like before the machined body is sintered. However, if the calcined body is too soft, the supports may break during cutting and fall off the calcined body before the machined body is completed. On the other hand, if the calcined body is too hard, separating the machined body from the supports from the frame that holds the machined body takes an excessive amount of time, and the tools wear out, making the separation difficult. Therefore, there is a need for a zirconia calcined body that can form supports that are less likely to break during cutting and that can be easily separated.

[0006] As a calcined zirconia body, for example, Patent Document 1 discloses a porous pre-sintered zirconia material that exhibits N2 adsorption and / or desorption of type IV isotherm according to the IUPAC classification and has a Vickers hardness of about 25 to 150.

[0007] Furthermore, Patent Document 2 discloses a calcined zirconia body obtained from a composition containing zirconia powder, each having a specific average particle size and 55% or more of which is monoclinic, and a stabilizer capable of suppressing the phase transition of zirconia. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2015-528730 [Patent Document 2] International Publication No. 2018 / 056330 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the inventors' investigations revealed that the porous pre-sintered zirconia material of Patent Document 1 has a high probability of chipping during cutting. Furthermore, with regard to the zirconia calcined body of Patent Document 2, when a composition that has undergone a primary crushing step is used as a method for producing the composition, the support often breaks during cutting due to the insufficient hardness of the zirconia calcined body, and the probability of chipping is high. Patent Document 2 also discloses a zirconia calcined body obtained from a composition that has undergone a secondary crushing step, but it was found that in this case, the probability of chipping is high.

[0010] Therefore, an object of the present invention is to provide a zirconia calcined body that has excellent machinability, can form supports that are not easily broken during cutting and can be easily separated, and has a low probability of chipping (hereinafter referred to as the "chipping rate" or "chipping incidence rate"), and a method for producing the same. [Means for solving the problem]

[0011] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by a zirconia calcined body that contains a specific amount of a stabilizer, at least a portion of which is not solid-dissolved in zirconia, and that has a specific Vickers hardness. Based on this finding, the present inventors have conducted further research and have completed the present invention.

[0012] That is, the present invention includes the following inventions. [1] A composition comprising zirconia and a stabilizer capable of suppressing the phase transition of zirconia, The content of the stabilizer is 3 to 8 mol% based on the total moles of zirconia and the stabilizer, At least a part of the stabilizer is not solid-dissolved in the zirconia, Vickers hardness measured in accordance with JIS Z 2244:2009 is 65 to 135 HV 5 / 30. Zirconia calcined body. [2] The zirconia calcined body according to [1], wherein the stabilizer is yttria. [3] The fraction of yttria not dissolved in zirconia calculated based on the following formula (1): y The zirconia calcined body according to [2], wherein is within the range shown in formula (2).

number

[10] A dental material comprising the zirconia calcined body according to any one of [1] to [9].

[11] A step of producing a zirconia composition comprising zirconia particles and particles made of a stabilizer capable of suppressing a phase transition of zirconia, wherein the content of the stabilizer is 3 to 8 mol% based on the total moles of zirconia and the stabilizer; and a step of firing the zirconia composition to obtain a zirconia calcined body having a Vickers hardness in accordance with JIS Z 2244:2009 of 65 to 135 HV 5 / 30, The manufacturing process of the zirconia composition includes a mixing step of mixing zirconia powder with the stabilizer to prepare a mixture, and a step of adding a binder to the mixture and granulating the mixture to obtain zirconia granules; and Substantially no firing process is involved; Method for producing zirconia calcined body.

[12] The method for producing a zirconia calcined body according to

[11] , wherein the content of the binder is 1.2 to 2.8 mass % based on the total mass of the zirconia composition.

[13] The method for producing a zirconia calcined body according to

[11] or

[12] , wherein the zirconia in the zirconia composition has a predominant crystal system of monoclinic.

[14] The method for producing a calcined zirconia body according to

[13] , wherein the proportion of monoclinic crystals in the zirconia crystal system is 55% or more.

[15] The method further comprises a step of press-molding the zirconia granules to obtain a zirconia molded body, The surface pressure of the press molding when producing the zirconia molded body is 30 to 200 MPa, The density of the zirconia calcined body is 2.7 g / cm 3 ~4g / cm 3The method for producing a zirconia calcined body according to any one of

[11] to

[14] , wherein

[16] A method for producing a calcined zirconia body according to

[15] , comprising a step of calcining the zirconia compact at 830 to 1080°C. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a zirconia calcined body and a method for producing the same that have excellent machinability, can form supports that are not easily broken during cutting and can be easily separated, and have a low probability of chipping. Furthermore, because the zirconia calcined body of the present invention has excellent machinability, it is possible to reduce the stress and time required for cutting and polishing after sintering. [Brief explanation of the drawings]

[0014] [Figure 1] 10 is an optical microscope photograph of the surface of a machined body with a chipping rate of 1% according to Example 3. [Figure 2] 1 is an optical microscope photograph of the surface of a machined body having a chipping rate of 10% according to Comparative Example 1. [Figure 3] FIG. 2 is a schematic view showing an example of the shape of a zirconia calcined body before cutting. [Figure 4] FIG. 2 is a schematic view showing an example of a machined body and a support pillar formed during machining of a zirconia calcined body. DETAILED DESCRIPTION OF THE INVENTION

[0015] The zirconia calcined body of the present invention contains zirconia (zirconium oxide) and a stabilizer (hereinafter simply referred to as "stabilizer") capable of suppressing the phase transition of zirconia, the stabilizer content being 3 to 8 mol% based on the total moles of zirconia and stabilizer, at least a portion of the stabilizer not being solid-dissolved in zirconia, and the Vickers hardness measured in accordance with JIS Z 2244:2009 is 65 to 135 HV 5 / 30.

[0016] The zirconia calcined body of the present invention will now be described. The zirconia calcined body can serve as a precursor (intermediate product) of a zirconia sintered body. In the present invention, the zirconia calcined body refers to, for example, a block of zirconia particles (powder) that is not completely sintered.

[0017] The zirconia calcined body 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), yttria, cerium oxide (CeO), scandium oxide (ScO), niobium oxide (NbO), lanthanum oxide (LaO), erbium oxide (ErO), and praseodymium oxide (PrO). 11 Examples of suitable stabilizers include oxides such as yttria, samarium oxide (Sm2O3), europium oxide (Eu2O3), and thulium oxide (Tm2O3), with yttria being preferred. The stabilizer content in the zirconia calcined body and sintered body thereof of the present invention can be measured by, for example, inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis, or the like. In the zirconia calcined body and sintered body thereof of the present invention, the stabilizer (suitably yttria) content is preferably 3.0 to 8.0 mol%, more preferably 3.2 to 6.5 mol%, even more preferably 3.5 to 6.0 mol%, and particularly preferably 3.9 to 5.4 mol%, based on the total moles of zirconia and stabilizer. If the content of the stabilizer is less than 3.0 mol%, the translucency of the zirconia sintered body will be insufficient, and if it exceeds 8.0 mol%, the amount of phases that undergo phase transition to tetragonal and / or cubic systems will increase, increasing the probability of chipping and, further, reducing the strength of the zirconia sintered body.

[0018] In the zirconia calcined body of the present invention, at least a portion of the stabilizer must not be solid-dissolved in zirconia. That is, at least a portion of the zirconia crystals must be monoclinic. The fact that a portion of the stabilizer is not solid-dissolved in zirconia can be confirmed, for example, by X-ray diffraction (XRD) patterns. If a peak attributable to the stabilizer is observed in the XRD pattern of the zirconia calcined body, this indicates that some stabilizer is present in the zirconia calcined body that is not solid-dissolved in zirconia. If the entire amount of stabilizer is solid-dissolved, essentially no peak attributable to the stabilizer is observed in the XRD pattern. However, depending on conditions such as the crystalline state of the stabilizer, even if no stabilizer peak is present in the XRD pattern, the stabilizer may not be solid-dissolved in zirconia. If the zirconia has a predominant crystalline system of tetragonal and / or cubic and no stabilizer peak is present in the XRD pattern, it is considered that most, essentially all, of the stabilizer is solid-dissolved in zirconia. In the zirconia calcined body of the present invention, the stabilizer does not necessarily have to be entirely dissolved in zirconia. In the present invention, the phrase "the stabilizer is dissolved in solid form" means, for example, that the elements (atoms) contained in the stabilizer are dissolved in solid form in zirconia.

[0019] The Vickers hardness of the zirconia calcined body of the present invention is 65 HV 5 / 30 or more, preferably 67 HV 5 / 30 or more, and more preferably 69 HV 5 / 30 or more. On the other hand, the lower the Vickers hardness, the easier it is to separate the machined body from the frame that holds it, suppressing tool wear and allowing for separation in a short time. Therefore, the Vickers hardness is 135 HV 5 / 30 or less, preferably 133 HV 5 / 30 or less, and more preferably 130 HV 5 / 30 or less. If the Vickers hardness is less than 65 HV 5 / 30, the chipping rate increases, while if it exceeds 135 HV 5 / 30, it becomes difficult to separate the machined body from the frame that holds it. The zirconia calcined body of the present invention has a Vickers hardness within the above-mentioned range, which, combined with the fact that at least a portion of the stabilizer is not solid-dissolved in zirconia, can reduce the probability of chipping. The method for measuring the Vickers hardness in the present invention conforms to JIS Z 2244:2009, and will be described in detail in the examples below.

[0020] In order to achieve the Vickers hardness of the zirconia calcined body of the present invention, the content of undissolved stabilizer in the zirconia calcined body, the density of the calcined body, the average particle size of the particles contained in the calcined body, and the strength of the calcined body are important. Furthermore, in order to achieve these factors, the production method of the zirconia calcined body and the zirconia composition is also important. The production method of the zirconia composition that does not substantially include a firing step, the binder content during the production of the composition, the contact pressure during the production of the zirconia molded body, and the calcination temperature during the production of the calcined body are also important. These are described below.

[0021] Hereinafter, a preferred embodiment will be described in which the zirconia calcined body contains yttria as a stabilizer. In the zirconia calcined body of the present invention, the abundance ratio f of yttria that is not solid-dissolved in zirconia (hereinafter sometimes referred to as "undissolved yttria") is y can be calculated based on the following formula (1):

[0022]

number

[0023] In equation (1), I y (111) indicates the peak intensity of the (111) plane of yttria at around 2θ=29° in the XRD pattern using CuKα radiation. m (111) and I m (11-1) indicates the peak intensity of the (111) and (11-1) planes of the monoclinic system of zirconia. t (111) indicates the peak intensity of the (111) plane of the tetragonal crystal system of zirconia. c (111) indicates the peak intensity of the (111) plane of the cubic crystal system of zirconia.

[0024] Zirconia is solid-solubilized with a stabilizer, i.e., the stabilizer and zirconia diffuse into each other, resulting in metastabilization or stabilization of the zirconia. It is known that when an external force is applied to metastabilized or stabilized zirconia, the external force is alleviated by a phase transformation. Therefore, the more the stabilizer disappears through solid solution (the greater the proportion of dissolved stabilizer), the more components there are that alleviate stress resulting from external forces, leading to increased chipping during cutting. Therefore, it is preferable that the stabilizer is not solid-solubilized.

[0025] In addition, the solid solution of zirconia and yttria is a phenomenon in which each atom moves to the other due to the concentration gradient of each atom. Therefore, the amount of solid solution changes depending on the yttria content. Therefore, the existence rate of undissolved yttria, f y varies depending on the yttria content.

[0026] Therefore, the fraction of undissolved yttria in the calcined zirconia body, f y From the viewpoint of Vickers hardness and chipping rate, it is preferable that the range shown by formula (2) corresponding to each yttria content is satisfied. f y ≧1.7×(yttria content)-3.6 (2) Specifically, when the yttria content is 4.0 mol%, yis preferably 3.2% or more, more preferably 4.1% or more, and even more preferably 5.1% or more. y is preferably 4.0% or more, more preferably 5.1% or more, and even more preferably 6.1% or more. y is preferably 4.3% or more, more preferably 5.4% or more, and even more preferably 6.4% or more. y is preferably 4.9% or more, more preferably 5.9% or more, and even more preferably 6.9% or more. y is preferably 5.4% or more, more preferably 6.5% or more, and even more preferably 7.5% or more. y is preferably 6.6% or more, more preferably 7.7% or more, and even more preferably 8.7% or more. y is preferably 10.0% or more, more preferably 11.1% or more, and even more preferably 12.2% or more. y When formula (2) is satisfied, the presence rate of the dissolved stabilizer decreases, and the chipping rate decreases. y If the ratio of undissolved yttria f satisfies the formula (2) and the Vickers hardness is within a predetermined range, the chipping rate can be further reduced. y When the amount of is a desired amount, the calcined zirconia body can exhibit a type III isotherm of nitrogen adsorption and / or desorption according to the IUPAC classification. The method for measuring the IUPAC classification is as described in the Examples below.

[0027] The density of the zirconia calcined body of the present invention is 2.7 to 4.0 g / cm from the viewpoint of achieving a preferable range of Vickers hardness and reducing the chipping rate. 3 is preferably 2.9 to 3.6 g / cm 3 More preferably, it is 3.1 to 3.4 g / cm 3 It is more preferable that the density is 2.7 g / cm 3If the density is less than 4.0 g / cm3, sufficient Vickers hardness cannot be obtained, and machinability may be reduced. 3 If the density is larger, the Vickers hardness may be too high, which may result in reduced machinability. The density can be calculated, for example, as (mass of calcined body) / (volume of calcined body). The density of the zirconia calcined body refers to the density of the calcined body obtained by filling zirconia granules into a specific mold (such as a metal mold) and forming a specific shape under pressure, heating the molded body at a temperature at which the binder can be removed, and then heating it at a temperature at which yttria is adequately solid-dissolved and necking (adhesion) is adequately formed. The temperature at which the binder is removed is not particularly limited as long as it is a temperature at which the binder can be removed, and may be 150 to 500°C. The temperature at which yttria is adequately solid-dissolved and necking (adhesion) is adequately formed is not particularly limited, and may be 800 to 1050°C.

[0028] In the zirconia calcined body of the present invention, at least a portion of the stabilizer is not dissolved in the zirconia. Therefore, in the zirconia calcined body of the present invention and the zirconia composition used to produce the same, it is necessary that at least a portion of the zirconia crystals be present in a monoclinic system, and it is preferable that the main crystal system of the zirconia be a monoclinic system. In the present invention, the term "main crystal system is a monoclinic system" refers to the ratio f of the monoclinic system in the zirconia calculated by the following formula (3) to the total amount of all crystal systems (monoclinic, tetragonal, and cubic) in the zirconia. m In the calcined zirconia body of the present invention, the monoclinic fraction f in the zirconia calculated by the following formula (3) is 50% or more. m is preferably 55% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, particularly preferably 80% or more, even more particularly preferably 85% or more, and most preferably 90% or more, based on the total amount of monoclinic, tetragonal, and cubic crystals. m can be calculated from the following formula (3) based on the peaks in the XRD pattern using CuKα radiation.

[0029] In the calcined zirconia body of the present invention, peaks of the tetragonal and cubic crystal systems may not be substantially detected. m can be set to 100%.

[0030]

number

[0031] The zirconia calcined body of the present invention contains an adhesion of particles made of a zirconia composition, and the degree of adhesion varies depending on the average particle size of these particles, which in turn affects the hardness of the calcined body. The smaller the average particle size of the particles, the more likely necking (adhesion) occurs during calcination. The average particle size (average primary particle size) of the particles constituting the granules is preferably 40 to 150 nm. An average particle size of 40 nm or more is preferred because adhesion is not strong and hardness is unlikely to increase. On the other hand, an average particle size of 150 nm or less is preferred because it is difficult to absorb small particles in the particle size distribution, making adhesion due to differences in particle size less likely to occur. The average particle size of the particles is more preferably 95 to 130 nm, and even more preferably 110 to 130 nm. The method for measuring the average particle size is as described in the Examples below.

[0032] The hardness during cutting is also affected by the strength of the calcined body. The strength of the zirconia calcined body according to the present invention can be evaluated, for example, by measuring the bending strength of the zirconia calcined body. The three-point bending strength of the zirconia calcined body, measured in accordance with JIS R 1601:2008, is preferably 15 MPa or more, more preferably 18 MPa or more, and even more preferably 20 MPa or more, in order to ensure strength sufficient for mechanical processing. If the three-point bending strength of the zirconia calcined body is less than 15 MPa, for example, during cutting to cut the machined body 2 having the desired shape shown in FIG. 4 from the zirconia calcined body 1 having the shape shown in FIG. 3, the support 3 (support or sprue) is likely to break, resulting in the support 3 falling off the zirconia calcined body before the desired machined body is obtained. Furthermore, in order to facilitate mechanical processing, the three-point bending strength of the zirconia calcined body is preferably 70 MPa or less, more preferably 60 MPa or less, even more preferably 50 MPa or less, and particularly preferably 40 MPa or less. From the above, taking into consideration the preferred range of Vickers hardness, the three-point bending strength of the zirconia calcined body is preferably 15 to 70 MPa, more preferably 18 to 60 MPa, further preferably 20 to 50 MPa, and particularly preferably 20 to 40 MPa.

[0033] A preferred embodiment is a dental material made of the above-mentioned zirconia calcined body. In dental products, surface smoothness is important from the viewpoint of aesthetics, and a low chipping rate of the zirconia calcined body is preferable. Furthermore, a low chipping rate is preferable in order to reduce the amount of work required to rework the machined body after firing it as a dental material. The chipping rate is preferably 9% or less, more preferably 7% or less, even more preferably 5% or less, particularly preferably 3% or less, and most preferably 1% or less. The method for measuring the chipping rate is as described in the Examples below.

[0034] A zirconia composition for producing the zirconia calcined body of the present invention will be described. The zirconia composition serves as a precursor to the above-mentioned zirconia calcined body of the present invention. In the present invention, the zirconia composition contains zirconia and a stabilizer. The contents of zirconia and stabilizer in the zirconia composition are calculated from the contents of a predetermined zirconia calcined body, and the contents in the zirconia composition and the zirconia calcined body are the same.

[0035] The zirconia composition includes powder, a fluid in which the powder is added to a solvent, and a molded body in which the powder is molded into a predetermined shape. When the zirconia composition is in the form of a powder, it may be an aggregate of granules. Granules are formed by agglomeration of primary particles.

[0036] In the present invention, the term "primary particle" refers to the smallest bulk unit. For example, primary particles refer to spherical bodies that are not bonded to each other and appear separable under an electron microscope (e.g., a scanning electron microscope). Primary particles include zirconia particles and stabilizer particles.

[0037] The particles constituting the zirconia composition granules are preferably primarily primary particles. Secondary particles are aggregates of primary particles. For example, when visually inspecting an electron microscope image, the number of primary particles is preferably greater than the number of secondary particles. Because secondary particles typically have irregular shapes, an increase in the number of secondary particles results in a decrease in the circularity of the granules, as described below.

[0038] The particle size of the primary particles constituting the zirconia composition granules affects the degree of adhesion during calcination and thus the hardness of the calcined body. An average particle size of 40 nm or more is preferred because the surface area of ​​the primary particles contained in the calcined body is reduced, preventing strong adhesion and less increase in hardness. On the other hand, an average particle size of 150 nm or less is preferred because it is difficult to absorb smaller particles in the particle size distribution, making it less likely for adhesion due to differences in particle size to occur. A range of 40 to 150 nm is preferred, with a range of 95 to 130 nm being more preferred, and a range of 110 to 130 nm being even more preferred.

[0039] The BET specific surface area of ​​the particles constituting the granules made of the zirconia composition is 7.0 m when measured in accordance with JIS Z 8830:2013. 2 / g or more, and 7.5m 2 / g or more is more preferable, and 8m 2 / g or more is more preferable. 2 / g or more, the sintered body can be prevented from becoming cloudy when sintered. 2 / g or less, and 2 / g or less is more preferable, and 20m 2 / g or less is more preferable. 2 / g or less, the sintered body is less susceptible to temperature variations in the sintering furnace. Furthermore, even if the sintering time is shortened, the translucency of the sintered body is less likely to decrease. The "BET specific surface area" here refers to the specific surface area measured without distinguishing between primary particles and secondary particles.

[0040] Of the zirconia in the zirconia composition, 50% or more, preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more can be in the form of granules.

[0041] When the zirconia composition does not take the form of granules, the zirconia particles constituting the powder may have the above-mentioned average particle size and, if necessary, the above-mentioned BET specific surface area.

[0042] The average particle size (secondary particle size, hereinafter also referred to as "average granule size") of the zirconia composition granules is preferably 10 μm or more, more preferably 12 μm or more, and even more preferably 14 μm or more. If the average granule size is less than 10 μm, air may be entrapped when the granules are placed in a mold, resulting in insufficient degassing during molding, and a uniform, dense molded body may not be produced. Furthermore, granules may be ejected from gaps during molding, resulting in a molded body that does not meet the required quantity. The average granule size is preferably 200 μm or less, more preferably 190 μm or less, even more preferably 180 μm or less, particularly preferably 150 μm or less, and most preferably 100 μm or less. If the average granule size exceeds 200 μm, cavities are likely to form inside the granules. Furthermore, gaps are likely to form when the granules are placed in a mold. These phenomena may result in insufficient degassing during molding, and a dense molded body may not be produced. Furthermore, shrinkage during molding may be significant, making it impossible to produce a molded body of the desired size. It is preferable that 50% or more of the zirconia in the zirconia composition constitute granules. The average granule particle size is preferably measured using a method that does not destroy the granules. The average granule particle size can be measured, for example, by dry sieving or wet sieving. The dry sieving method can be measured according to the sieving test method described in JIS Z 8815:1994, and manual sieving or mechanical sieving can be used, with mechanical sieving being preferred. The sieves used in the sieving method can be those described in JIS Z 8801-1:2019 Test Sieves. The measuring device used in the sieving method can be, for example, a rotary sieve shaker or an ultrasonic vibration sieving measuring instrument. An example of a low-tap type sieve shaker is the "RPS-105M" manufactured by Seishin Enterprise Co., Ltd. An example of an ultrasonic vibration type sieving measuring instrument is the "Robot Sifter RPS-01" or "Robot Sifter RPS-02" manufactured by Seishin Enterprise Co., Ltd.

[0043] It is preferable that the sphericity of the granules in the zirconia composition is high. Increasing the sphericity of the granules can induce mixing at the interface between layers when zirconia powders of different compositions are layered. Furthermore, when filling a mold with zirconia powder to produce a compact, a higher sphericity can increase the packing density even if the average particle diameter is the same. By increasing the packing density, which is the density of a compact formed by filling zirconia granules into a specific mold (such as a metal mold) and pressurizing it to a specific shape, the strength and translucency of the sintered body can be increased. Furthermore, even if the mold has corners, the packing property of the granules at the corners can be improved.

[0044] The sphericity of the granules in the zirconia composition can be expressed, for example, by the loose bulk density, the packed bulk density, or the like.

[0045] The zirconia composition has a bulk density of 1.0 g / cm 3 It is preferable that the concentration is 1.1 g / cm or more. 3 More preferably, it is 1.2 g / cm or more. 3 More preferably, it is 1.3 g / cm or more. 3 The lightly packed bulk density can be measured in accordance with JIS R 9301-2-3:1999.

[0046] The compacted bulk density of the zirconia composition is 1.3 g / cm 3 It is preferable that the concentration is 1.4 g / cm or more. 3 More preferably, it is 1.5 g / cm or more. 3 The compacted bulk density can be measured in accordance with JIS R 9301-2-3:1999.

[0047] The zirconia composition preferably includes a binder.

[0048] Examples of the binder include organic binders. Examples of organic binders include commonly used acrylic binders, acrylic acid binders, paraffin 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 are more preferred, and water-soluble polyacrylates are even more preferred. The polyacrylates may be copolymers of acrylic acid or methacrylic acid with maleic acid, or may contain sulfonic acid, and examples of the salt cations include sodium and ammonium.

[0049] The content of the binder in the zirconia composition is important for adjusting the distance between primary particles in the zirconia composition and for increasing or decreasing the Vickers hardness or the strength of the calcined body. The binder content is preferably 1.2 to 2.8 mass% of the entire zirconia composition, more preferably 1.5 to 2.5 mass%, and even more preferably 1.8 to 2.2 mass%. If the binder content is less than 1.2 mass% of the entire zirconia composition, the strength of the calcined body may increase, which may make the machined body hard to remove. If the binder content is more than 2.8 mass%, the strength of the calcined body may decrease, increasing the possibility that the machined body may fall off, and in addition, the chipping rate may increase.

[0050] The zirconia composition may optionally contain additives such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (Al2O3), titanium oxide (TiO2), silica (SiO2), dispersants, and antifoaming agents. These components may be used alone or in combination. 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 agent include Y2SiO5:Ce, Y2SiO5:Tb, (Y, Gd, Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl 10 O 17 :Eu, etc.

[0051] The additives may be added during mixing or pulverization, or may be added after pulverization.

[0052] Examples of methods for producing a zirconia calcined body include a step of producing a zirconia composition containing zirconia particles and particles made of a stabilizer capable of suppressing the phase transition of zirconia, wherein the stabilizer content is 3 to 8 mol % based on the total moles of zirconia and the stabilizer, and a step of firing the zirconia composition to obtain a zirconia calcined body having a Vickers hardness of 65 to 135 HV 5 / 30 according to JIS Z 2244: 2009. First, the production step of the zirconia composition will be described.

[0053] First, zirconia (preferably zirconia particles) and a stabilizer are mixed in a predetermined ratio to prepare a mixture (mixing step). For example, when the stabilizer is yttria, the zirconia and yttria can be mixed in a ratio such that the yttria content is as described above. Mixing is not particularly limited, and a known mixing device can be used. When a solvent is used for mixing, the resulting mixture may be in the form of a slurry or the like. The solvent is not particularly limited, and water or an organic solvent can be used. Mixing may be performed by dry mixing or wet mixing. The zirconia particles contained in the zirconia composition can be pulverized to have the above-mentioned average particle size (preferably 0.10 μm to 0.14 μm), and if necessary, until the zirconia particles have a BET specific surface area (pulverization step). The average primary particle size can be measured by a laser diffraction / scattering particle size distribution measurement method. For example, using a laser diffraction / scattering particle size distribution analyzer (trade name "Partica LA-950") manufactured by Horiba, Ltd., a slurry diluted with water can be irradiated with ultrasound for 30 minutes, and then the volumetric measurement can be performed while applying ultrasound. The mixing step and the pulverization step can be performed in the same step. The pulverization method is not particularly limited, and can be performed using a known pulverization device (e.g., a ball mill, a bead mill, etc.). The binder can be added in the mixing step and / or the pulverization step so that the binder content in the entire zirconia composition becomes the predetermined ratio described above. After the mixing step and / or the pulverization step, the resulting mixture can be dried by spray drying to form the zirconia composition in the granular form described above (drying step). The spray drying method is not particularly limited, and a known spray drying device (e.g., a spray dryer) can be used. This allows the zirconia composition of the present invention to be produced. In the zirconia composition, it is preferable that the main crystal system of zirconia is a monoclinic system. It is also preferable that the production of the zirconia composition does not substantially include a firing step. The phrase "substantially does not include a firing step" means that the production of the zirconia composition does not include any heat treatment other than a drying step such as spray drying, in order to suppress the formation of a solid solution of the stabilizer in zirconia from the viewpoint of reducing the chipping rate.The temperature of the substantially non-containing firing step is not particularly limited, but may be 800°C or higher, or 900°C or higher.

[0054] In the pulverization step, the average particle size of the zirconia composition is preferably less than 0.13 μm, more preferably 0.125 μm or less, even more preferably 0.12 μm or less, and particularly preferably 0.115 μm or less. By making the average particle size of the zirconia composition less than 0.13 μm, the translucency of the sintered body can be improved.

[0055] It is preferable to prepare the zirconia and the stabilizer separately. For example, it is preferable that the zirconia and the stabilizer are not precipitated simultaneously (in the same process), but that the zirconia preparation process (e.g., manufacturing process) and the stabilizer preparation process (e.g., manufacturing process) are separate, independent processes. This makes it possible to prevent the stabilizer from dissolving in zirconia during the calcined body manufacturing process described below.

[0056] In addition, in general, in the production of zirconia compositions, a stabilizer may be dissolved in zirconia by heat treatment, and then the resulting composition may be subjected to additional milling and drying processes. However, as the dissolution of the stabilizer progresses, a phase that undergoes thermal phase transition to a tetragonal and / or cubic system is generated, resulting in an increased chipping rate. Therefore, heat treatment of the zirconia composition is not preferred in the present invention. In the present invention, in order to reduce the chipping rate and to suppress the dissolution of the stabilizer, a production method that produces granules or powder without additional heat treatment other than a drying process such as spray drying is preferred. Furthermore, because the energy required for mixing and milling can sometimes promote the dissolution of the stabilizer, a production method that involves fewer mixing and milling steps is preferred.

[0057] On the other hand, zirconia powder containing yttria as a solid solution is generally produced by coprecipitation and hydrolysis. In the coprecipitation and hydrolysis methods, a mixture of hydrated zirconia and yttria is produced from zirconium oxychloride and yttrium chloride in the same process, and this mixture is fired at 800°C to 900°C to produce a stabilized zirconia powder containing yttria (yttrium) as a solid solution. The main crystal system of this yttria-doped zirconia is tetragonal and / or cubic. The particle size of the resulting zirconia powder is on the order of several tens of nanometers. To use this zirconia powder as a raw material for a zirconia sintered body, the fired product is pulverized to a predetermined particle size and then granulated to produce a zirconia composition.

[0058] In the case of zirconia compositions prepared by such coprecipitation or hydrolysis methods, the bonding temperature in the temperature range for preparing the calcined body is close to the temperature for removing the organic binder, and / or the temperature dependency is high. If the organic binder is present in an uneven state, the primary particles of the zirconia composition prepared by the coprecipitation or hydrolysis method will form strong localized necking depending on their particle diameter. Therefore, the chipping rate of the machined body will increase, and therefore zirconia compositions prepared by the coprecipitation or hydrolysis method are not preferred.

[0059] The granules or powder can be molded into a molded body by applying an external force. The molding method is not limited to a specific method, and a suitable method can be selected depending on the purpose. For example, molding can be performed by press molding, injection molding, stereolithography, etc. Multi-stage molding may also be performed. For example, the zirconia composition may be press-molded and then further subjected to CIP treatment to form a molded body.

[0060] The shaped body may have the shape of a disk, a rectangular parallelepiped, a cylinder, or a dental product (for example, a dental crown).

[0061] For example, the zirconia molded body may be a columnar zirconia molded body obtained by filling a mold with zirconia granules and compacting them with a uniaxial press. The higher the surface pressure in the press molding, the higher the density of the molded body. On the other hand, if the density of the zirconia molded body is too high, the zirconia calcined body will be too hard. Therefore, the surface pressure in the press molding when producing the zirconia molded body is preferably 30 to 200 MPa. When the surface pressure in the press is 30 MPa or more, the shape retention of the zirconia molded body is excellent, and when it is 200 MPa or less, the density of the zirconia molded body does not increase too much, making it easier to prevent hardening. The zirconia granules or zirconia composition obtained by the above-mentioned method for producing a zirconia composition are press-molded at a predetermined surface pressure and calcined at the calcination temperature described below, thereby obtaining the desired Vickers hardness and related physical properties (such as strength).

[0062] The molded body also includes a molded body densified by high-temperature pressure treatment such as CIP (Cold Isostatic Pressing) treatment, etc. From the same viewpoint as above, the water pressure is preferably 30 to 200 MPa.

[0063] The zirconia calcined body of the present invention serves as a precursor (intermediate product) of the zirconia sintered body of the present invention, which will be described later. The calcined body is obtained by firing (i.e., calcining) a zirconia composition at a temperature below sintering, and refers to, for example, a state in which zirconia particles (powder) are necked (adhered together) and not completely sintered. The calcined body also includes a shaped body. The zirconia calcined body of the present invention also includes, for example, a dental product (e.g., a crown-shaped prosthesis) obtained by processing a calcined zirconia disk using a CAD / CAM (Computer-Aided Design / Computer-Aided Manufacturing) system.

[0064] The contents of zirconia and stabilizer in the zirconia calcined body of the present invention are the same as those in the zirconia composition before the zirconia calcined body is produced. From the viewpoints of strength and translucency of a sintered body produced from the zirconia calcined body of the present invention, the stabilizer is preferably yttria.

[0065] As described above, the proportion of undissolved yttria in the zirconia calcined body of the present invention is determined by the ratio f y The preferable range is as described above, but it depends on the calcination temperature when preparing the zirconia calcined body.

[0066] That is, the calcination temperature affects the Vickers hardness or strength of the calcined body, and the hardness and chipping rate of the calcined body change depending on the calcination temperature.

[0067] From the above viewpoints, the calcination temperature (maximum calcination temperature) in the method for producing a zirconia calcined body of the present invention 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 lower than 830°C, the support connecting a part of the zirconia calcined body produced by the production method satisfying the above-mentioned predetermined conditions to the cut body may break, making the cut body more likely to fall off during cutting. In addition, the Vickers hardness may decrease, resulting in an increased chipping rate. Furthermore, if the calcination temperature is higher than 1080°C, adhesion may progress and the cut body may become too hard. This may require time to separate the cut body from the frame holding it, and may increase tool wear, making separation difficult. Furthermore, depending on the stabilizer content, the amount of the stabilizer in solid solution may increase, generating a phase that undergoes a thermal phase transition to a tetragonal and / or cubic system, which may increase the chipping rate.

[0068] Holding the maximum calcination temperature for a certain time brings the hardness of the calcined body into a desirable range and may reduce the chipping rate, so the maximum calcination temperature is preferred. The calcination conditions depend on the density of the calcined body, the average particle size of the calcined body, and the binder content, but it is preferable to hold the calcination temperature at the maximum calcination temperature for 30 minutes to 6 hours, and it is also preferable that the temperature rise rate and temperature fall rate are 300°C / min or less.

[0069] The zirconia calcined body of the present invention can be machined to produce a machined body. The cutting method is not limited to a specific method, and a suitable method can be selected depending on the purpose. For example, a machined body can be produced by cutting a zirconia disk, which is also a calcined body, into the shape of a dental product (e.g., a crown-shaped prosthesis) using a CAD / CAM system.

[0070] The surface smoothness of the machined body may be improved using a tool such as a pearl surface.

[0071] A zirconia sintered body (hereinafter, sometimes simply referred to as a "zirconia sintered body" or "sintered body") can be produced by subjecting the zirconia calcined body of the present invention or a machined body thereof to a sintering step in which the calcined body is fired at a temperature at which the zirconia particles are sintered (sinterable temperature). The firing temperature is preferably, for example, 1400°C or higher, and more preferably 1450°C or higher. The firing temperature is preferably, for example, 1650°C or lower, and more preferably 1600°C or lower. The heating rate and cooling rate are preferably 300°C / min or lower.

[0072] In the sintering step, the holding time at the sinterable temperature (for example, 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.

[0073] The zirconia calcined body of the present invention can shorten the firing time required to produce a sintered body without reducing the translucency and strength of the resulting zirconia sintered body. In particular, the holding time at the maximum firing temperature required to produce a sintered body can be shortened (short-time sintering). This improves production efficiency, and when the zirconia calcined body of the present invention is used in dental products, it shortens the time required from determining the dimensions of the dental product to be used in treatment and cutting it to making the dental product ready for treatment, thereby reducing the time burden on patients. It also reduces energy costs.

[0074] In the sintering step, the holding time at the sinterable temperature (for example, the maximum firing temperature) can be, for example, 25 minutes or less, 20 minutes or less, or 15 minutes or less.

[0075] The temperature increase and decrease rates in the sintering step are preferably set so as to shorten the time required for the sintering step. For example, the temperature increase rate can be set so as to reach the maximum firing temperature in the shortest time possible, depending on the performance of the firing furnace. The temperature increase rate to the maximum firing 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 temperature decrease rate is preferably set so as not to cause defects such as cracks in the sintered body. For example, after heating is completed, the sintered body can be allowed to cool at room temperature.

[0076] The zirconia sintered body obtained by sintering the zirconia calcined body of the present invention or a machined body thereof will now be described. The zirconia sintered body can be, for example, a zirconia particle (powder) in 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 actual density measured by Archimedes' method to the theoretical density. The relative density refers to the density d1 of a sintered body obtained by filling granules into a specific mold and shaping the molded body into a specific shape under pressure, and then sintering the sintered body at a high temperature, divided by the theoretical density d2 of zirconia (not including voids inside).

[0077] The zirconia sintered body includes not only a sintered body obtained by sintering molded zirconia particles under normal pressure or under no pressure, but also a sintered body obtained by densifying the zirconia particles by high-temperature pressure treatment such as HIP (hot isostatic pressing).

[0078] The density of the zirconia sintered body is preferably in the range of 5.71 g / cm because the higher the density, the fewer the internal voids and the less light scattering there is, which improves the translucency. 3 Preferably, it is greater than 5.87 g / cm 3 More preferably, the thickness is equal to or greater than 100 μm, and even more preferably, the thickness is substantially free of voids.

[0079] The particle size of the particles contained in the zirconia sintered body is preferably in the range of less than 0.588 μm, more preferably 0.5 μm or less, and even more preferably 0.3 μm or less, since the more particles contained in the zirconia sintered body are smaller than the wavelength of visible light, the higher the light transmittance and strength.

[0080] The content of zirconia and stabilizer in the zirconia sintered body is the same as that in the composition before the sintered body is produced and / or in the calcined body. Regarding the crystal system of zirconia in the sintered body, the proportion of monoclinic zirconia is preferably 10% or less, more preferably 5% or less, and even more preferably substantially absent (considered to be 0%). Crystal systems other than monoclinic zirconia are tetragonal and / or cubic.

[0081] Regarding the proportion of the stabilizer dissolved in the zirconia sintered body, it is preferable that 95% or more of the stabilizer is dissolved in the zirconia, and it is more preferable that substantially all of the stabilizer is dissolved in the zirconia. y is preferably 5% or less, more preferably 1% or less, and even more preferably, all of it is substantially in solid solution (0%).

[0082] The translucency of the zirconia sintered body is preferably 12 or higher, more preferably 14 or higher, even more preferably 15 or higher, and even more preferably 16 or higher. The translucency here refers to the L* value of the lightness (color space) in the L*a*b* color system (JIS Z 8781-4:2013). The L* value measured on a 1.2 mm thick sample against a white background is designated as the first L* value. The L* value measured on the same sample against a black background is designated as the second L* value. The second L* value is then subtracted from the first L* value. Regarding sample preparation, the granules (composition) are first press-molded to a thickness of 1.2 mm, followed by CIP molding to produce a disk-shaped compact with a diameter of, for example, 19 mm. The compact is then fired under specified firing conditions to produce a 1.2 mm thick sintered body. To measure the L* value, a contact liquid is applied to the surface of a sample, and then the L* values ​​of the black and white backgrounds are measured using a color difference meter (e.g., CE100-DC / JP, dental color measurement device "Crystal Eye" (manufactured by Olympus Corporation)). The contact liquid may have a refractive index nD of 1.60 measured at a measurement wavelength of 589 nm (sodium D line).

[0083] The zirconia sintered body may be a molded body having a predetermined shape. For example, the sintered body may have a disk shape, a rectangular parallelepiped shape, a dental product shape (e.g., a dental crown shape), or the like.

[0084] The methods for producing the zirconia composition, granules, powder, molded body, calcined body, machined body, and sintered body described in this specification 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 can be obtained.

[0085] The zirconia calcined body of the present invention can be suitably used for zirconia processed products that require strength and / or aesthetics after firing (e.g., dental materials, optical fiber cable connectors, smartphone housings, etc.) Examples of dental materials include dental prostheses such as crowns and inlays.

[0086] The present invention includes embodiments in which the above-described configurations are combined in various ways within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved. [Example]

[0087] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0088] [Evaluation of finger stiffness] The calcined bodies obtained in the following Examples and Comparative Examples were machined into a dental crown shape using a CAD / CAM system. The machined body was integrated with the calcined body by a support (cylindrical shape with a diameter of 5 mm) made of a part of the calcined body. Using an ULTIMATE 500 (manufactured by Nakanishi Co., Ltd.) equipped with a Diamond Point HP Model No. 25 (manufactured by Shofu Co., Ltd.), the support portion was pressed against the support perpendicularly to the direction of the support at 10,000 rpm in the air with a load of approximately 500 g. The cutting process was performed while visually inspecting (n=10) according to the following evaluation criteria. If 8 or more of the 10 samples met the evaluation criteria, the sample was judged to meet the criteria. A score of ◯ was determined to be acceptable. <Evaluation criteria> 〇: More than 90% of the support was removed within 10 seconds ×: The support could not be cut within 10 seconds (too hard) ××: The support broke within 10 seconds before more than 90% of the support was worn down (too soft)

[0089] [Chipping rate measurement] The calcined bodies obtained in the following Examples and Comparative Examples were machined into the shape of an anterior tooth frame using a diamond-coated end mill on a Kuraray Noritake Dental Co., Ltd. milling machine "DWX-52DC" based on 3D NC data. The machining pattern was contour machining, with a spindle rotation speed of 30,000 rpm, a feed rate of 2,000 mm / min, and a machining pitch of Z = 0.5 mm. Images of the center of the labial surface of the resulting anterior tooth were taken with an optical microscope. Chipped areas were painted black, and the remaining areas were designated white (binarized). The chipping rate was expressed as the percentage of the black area relative to the total area of ​​black and white. Area measurements were performed using Image-Pro Plus from Hakuto Co., Ltd. The evaluation criteria were as follows (n = 4). Figure 1 shows an optical microscope photograph of the surface of a machined body with a chipping rate of 1% in Example 3, and Figure 2 shows an optical microscope photograph of the surface of a machined body with a chipping rate of 10% in Comparative Example 1. A grade of fair or better was considered acceptable. <Judgment criteria> ◎◎: 1% or less ◎: More than 1% but less than 3% ○: More than 3% and less than 5% △: More than 5% and less than 7% ×: If it is greater than 7%

[0090] [Vickers hardness measurement] The calcined bodies obtained in the following Examples and Comparative Examples were used for measurement in accordance with JIS Z 2244: 2009. Using a Falcon 500 manufactured by Innovatest, a load of 5 kgf was held for 30 seconds, and the Hv value was calculated (average value of n=10).

[0091] [Density measurement] The dimensions of the rectangular parallelepiped calcined bodies, approximately 20 mm long x 19 mm wide x 17 mm high, obtained by the methods of the following Examples and Comparative Examples were accurately measured using a micrometer, and the mass was measured using a precision balance, and the density was calculated by dividing the mass of the calcined body by the volume of the calcined body (average value of n=3).

[0092] [Measuring average particle size] Using the calcined bodies obtained in the following examples and comparative examples, surface images were taken with a scanning electron microscope (product name "VE-9800", manufactured by Keyence Corporation). The average particle diameter was calculated from the obtained images by image analysis. Particle diameters were measured using Image-Pro Plus manufactured by Hakuto Co., Ltd. The captured SEM images were binarized, and the brightness range was adjusted to clearly show the grain boundaries. The particles were then recognized from the field of view (region). For areas where the grain boundaries were unclear, a degeneration filter was applied to the region, and each region was degenerated until it became one or more points. A Voronoi polygon was then drawn so that these points became the core points of the Voronoi polygon. A line connecting the midpoints of two adjacent core points was drawn, and the line was then superimposed on the original particle image to separate adjacent particles. For example, in image processing, a single particle may appear gourd-shaped. In such cases, the particle was separated into two by assuming that two circular particles were in contact and appearing as one. In the processing file that recognized the primary particle size, "Diameter" was selected in the "Count / Size Dialog" and the distribution was calculated (n = 4). Specifically, for four fields of view of one sample, the average particle size (primary particle size) was measured in each field using Image-Pro Plus software and the average value was calculated.

[0093] [Measurement of the presence rate of stabilizers] Using the calcined bodies obtained in the following Examples and Comparative Examples, XRD patterns were measured using a fully automatic multipurpose X-ray diffractometer (trade name "SmartLab Studio II") manufactured by Rigaku Corporation. The tube voltage was 40 kV-30 mA, the scan axis was the 2θ / θ method, and sampling was performed every 0.01 degrees at 4 degrees / minute. A high-resolution, high-speed one-dimensional X-ray detector (trade name "D / teX Ultra 250") was used as the detector. From the obtained XRD patterns, f in the above formula (1) was determined. y was determined (average value of n=3). As mentioned above, it is preferable that the range satisfying formula (2) is met. The criteria for evaluation are shown in Table 1. <Judgment criteria>

[0094] [Table 1]

[0095] [Measurement of three-point bending strength] The calcined bodies obtained in the following Examples and Comparative Examples were used in accordance with ISO 6872:2015. Test specimens measuring 5 mm × 10 mm × 50 mm were prepared, and the test specimen faces and C-face (see 7.3.1.2.1 of ISO 6872:2015) were sanded longitudinally with 600-grit sandpaper. The test specimens were positioned so that the widest face faced vertically (the load direction), and the three-point bending strength was measured using a universal testing machine (Shimadzu Corporation, "AG-I 100kN") at a span (distance between supports) of 30 mm and a crosshead speed of 0.5 mm / min (average value of n = 3).

[0096] [IUPAC classification measurement] The IUPAC classification was measured (n=2) under the following conditions using an Anton Paar fully automated gas adsorption analyzer (AS1-MP). Based on the IUPAC classification of adsorption / desorption isotherms, the shapes of the adsorption / desorption isotherms of the two samples were confirmed to fall within the IUPAC classification. For example, if both samples fell into Type IV, they were judged to be "Type IV." Comparative Examples 3 and 4 were Type IV of the IUPAC classification, and the others were Type III. Sample: The prepared zirconia calcined body was crushed in a mortar and passed through a sieve with a nominal mesh size (JIS Z8801-1:2019) of 63 μm. Degassing conditions: The sample was placed in a measurement cell and degassed at 200°C (under vacuum) for 2 days. Cell size: 1.5cm 3 (Stem outer diameter: 6mm) Adsorption gas: Nitrogen Measurement items: Adsorption / desorption isotherms at any measurement point (130 points in total) Analysis items: specific surface area by BET multipoint method, total pore volume, average pore diameter Pore ​​size distribution by BJH method (mesopore region) Pore ​​size distribution by NLDFT method (micropore to mesopore region)

[0097] <Examples 1 to 11, Comparative Examples 1, 2, 5 to 7> Separately prepared zirconia raw material (zirconium oxide) and yttria raw material (yttrium oxide) were weighed to achieve the yttria content (yttria content relative to the total moles of zirconia and stabilizer) shown in Table 2 and then added to water. This and zirconia beads were placed in a rotating container and mixed and pulverized using a ball mill until the raw materials reached the desired primary particle size (approximately 100 nm). The primary particle size was measured using a laser diffraction / scattering particle size distribution analyzer (product name "Partica LA-950") manufactured by Horiba, Ltd., by ultrasonicating the water-diluted slurry for 30 minutes and then measuring the primary particle size on a volume basis while applying ultrasonic waves. The desired slurry was obtained after approximately 20 hours of ball milling. Next, an organic binder was added to this slurry, except for Comparative Example 5. A water-based acrylic binder was used as the organic binder. The organic binder was added to the slurry in the amount shown in Table 2 and stirred with a rotary impeller for 24 hours. The stirred slurry was dried and granulated using a spray dryer to obtain granules. The average particle size of the granules was 40 μm. The powder consisting of these granules was poured into a cylindrical mold and uniaxially pressed at a pressure of 30 MPa, followed by a CIP treatment at 170 MPa to obtain a zirconia compact. The zirconia compact was placed in an electric furnace, heated from room temperature at a rate of 10°C / min, and held at 500°C for 2 hours to degrease the organic components. The zirconia compact was then held at the calcination temperature shown in Table 2 for 2 hours and slowly cooled at -0.4°C / min to obtain a calcined zirconia body.

[0098] <Comparative Examples 3 and 4> Zirconium oxychloride and yttrium chloride were mixed to obtain the oxide equivalent contents shown in Table 2, to obtain a mixture of hydrated zirconia and hydrated yttria. This mixture was fired at 800°C to obtain a stabilized zirconia powder containing yttria as a solid solution.

[0099] The average particle size was 40 nm when the slurry was subjected to a ball mill treatment in the same manner as in Example 1. After adding an organic binder to this slurry, the procedure was the same as in Example 1 to obtain a compact and a calcined body.

[0100] <Comparative Examples 8 and 9> The desired slurry was obtained in the same manner as in Example 1, with a ball mill treatment time of approximately 20 hours according to Table 2. The slurry was dried using a spray dryer without adding an organic binder, and the resulting powder was fired at the temperature shown in Table 2. Twice the mass of water and organic binder were added to the obtained powder, and the raw materials were mixed and pulverized using a ball mill until the desired primary particle size (approximately 100 nm) was achieved. The primary 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 water-diluted slurry with ultrasonic waves for 30 minutes, followed by volumetric measurement while applying ultrasonic waves. The desired slurry was obtained after a ball mill treatment time of approximately 20 hours. A water-based acrylic binder was used as the organic binder. The obtained slurry was then dried and granulated using a spray dryer to obtain granules. The average particle size of the granules was 40 μm. The powder consisting of these granules was poured into a cylindrical mold and uniaxially pressed at a pressure of 30 MPa while the mold was vibrated, followed by a CIP treatment at 170 MPa to obtain a compact. The compact was placed in an electric furnace, heated from room temperature at a rate of 10°C / min, and held at 500°C for 2 hours to degrease the organic components. The compact was then held at the secondary calcination temperature listed in Table 2 for 2 hours and slowly cooled at -0.4°C / min to obtain a calcined body.

[0101] The results of each example and comparative example are shown in Table 2.

[0102] [Table 2]

[0103] As a result, it was found that Examples 1 to 11, which contained a specific content of yttria as a stabilizer, at least a portion of which was not solid-dissolved in zirconia, and had a specific Vickers hardness, had good hardness to the touch and chipping rate, and were zirconia calcined bodies with excellent machinability. On the other hand, Comparative Examples 1 to 3 and 5 to 9, which did not have an appropriate Vickers hardness, and Comparative Examples 3 and 4, in which the stabilizer was solid-dissolved, had poor chipping rate or did not meet the standard for hardness to the touch. In particular, it was found that Comparative Example 4, even though the Vickers hardness was within the range of the present invention, had a poor chipping rate due to the presence of a solid-dissolved stabilizer. [Industrial Applicability]

[0104] The zirconia calcined body of the present invention can be suitably used for zirconia processed products (for example, dental materials, optical fiber cable connectors, smartphone housings, etc.). [Explanation of symbols]

[0105] 1. Zirconia calcined body 2 Cutting workpiece 3 pillars

Claims

1. Contains zirconia and a stabilizer capable of suppressing the phase transition of zirconia, the content of the stabilizer is 3 to 8 mol% based on the total moles of zirconia and the stabilizer, At least a part of the stabilizer is not solid-dissolved in the zirconia, The composition contains an aggregate of particles containing zirconia and a stabilizer, and the particles have an average particle size of 40 nm to 150 nm; The Vickers hardness measured in accordance with JIS Z 2244:2009 is 65 to 125 HV 5 / 30, Density is 2.7 g / cm 3 ~4g / cm 3 That is, Zirconia calcined body.

2. The zirconia calcined body according to claim 1 , wherein the stabilizer is yttria.

3. The abundance rate f of yttria not dissolved in zirconia was calculated based on the following formula (1): y The zirconia calcined body according to claim 2, wherein is in the range represented by formula (2). [Equation 1] f y ≧1.7×(yttria content)−3.6 (2) (In the formula, I y (111) indicates the peak intensity of the (111) plane of yttria at around 2θ=29° in the X-ray diffraction pattern using CuKα radiation, I m (111) and I m (11-1) indicates the peak intensity of the (111) plane and (11-1) plane of the monoclinic system of zirconia in the X-ray diffraction pattern, I t (111) indicates the peak intensity of the (111) plane of the tetragonal system of zirconia in the X-ray diffraction pattern, I c (111) indicates the peak intensity of the (111) plane of the cubic crystal system of zirconia in the X-ray diffraction pattern, The yttria content indicates the mol% of yttria relative to the total mol of zirconia and yttria.

4. 4. The zirconia calcined body according to claim 1, wherein the zirconia calcined body exhibits a type III nitrogen adsorption and / or desorption isotherm according to the IUPAC classification.

5. 5. The zirconia calcined body according to claim 1, which contains an aggregate of particles containing zirconia and a stabilizer, and the particles have an average particle size of 95 to 130 nm.

6. The zirconia calcined body according to any one of claims 1 to 5, wherein the content of the stabilizer is 3.2 to 6.5 mol% based on the total moles of zirconia and the stabilizer.

7. The zirconia calcined body according to any one of claims 1 to 6, having a three-point bending strength measured in accordance with JIS R 1601:2008 of 15 to 70 MPa.

8. The zirconia calcined body according to any one of claims 1 to 7, wherein the chipping rate after cutting is 9% or less.

9. A dental material comprising the zirconia calcined body according to any one of claims 1 to 8.

10. a step of producing a zirconia composition comprising zirconia particles and particles made of a stabilizer capable of suppressing a phase transition of zirconia, the stabilizer having a content of 3 to 8 mol% relative to the total moles of zirconia and the stabilizer; and a step of firing the zirconia composition to obtain a zirconia calcined body having a Vickers hardness in accordance with JIS Z 2244:2009 of 65 to 135 HV 5 / 30, the manufacturing process of the zirconia composition includes a mixing step of mixing a zirconia powder with the stabilizer to prepare a mixture, and a step of adding a binder to the mixture and granulating the mixture to obtain zirconia granules, and does not substantially include a firing step; The term "substantially not including the firing step" means that This means that it does not include any heat treatment other than the drying process and does not include any heat treatment at 800°C or higher. Method for producing zirconia calcined body.

11. The method for producing a zirconia calcined body according to claim 10, wherein the content of the binder is 1.2 to 2.8 mass% based on the entire zirconia composition.

12. 12. The method for producing a zirconia calcined body according to claim 10, wherein the zirconia in the zirconia composition has a predominant crystal system of monoclinic.

13. The method for producing a zirconia calcined body according to claim 12, wherein the proportion of monoclinic crystals in the zirconia crystal system is 55% or more.

14. The method further comprises a step of press-molding the zirconia granules to obtain a zirconia molded body, the surface pressure of the press molding when producing the zirconia molded body is 30 to 200 MPa, The density of the zirconia calcined body is 2.7 g / cm 3 ~4g / cm 3 The method for producing a zirconia calcined body according to any one of claims 10 to 13,

15. The method for producing a zirconia calcined body according to claim 14, comprising a step of calcining the zirconia compact at 830 to 1080 ° C.

Images