Zirconia calcined body

Abstract

The present invention provides a zirconia calcined body which achieves a relative density of at least 99.0% in high-speed firing at a high-speed temperature increase of 350°C / min, and from which a zirconia sintered body having excellent translucency is obtained. The present invention pertains to a zirconia calcined body which contains zirconia and yttria, and for which when six target temperatures are set from 1150°C to 1400°C at an interval of 50°C and six samples are prepared by increasing the temperatures of the samples up to the six respective different target temperatures at a temperature increase rate of 350°C / min from a temperature range of at most 400°C, and by maintaining the temperatures at the respective target temperatures for 10 minutes and then lowering the temperatures to 25°C, and when the temperature interval of the target temperatures from 1150°C to 1400°C is 50°C, and, for the six samples, the amount of the change between the density of the calcined body at the upper limit temperature and the density of the calcined body at the lower limit temperature in an n-th section (n represents an integer of at least 1) is denoted as Δρn, and the amount of the change in the temperature is denoted as ΔT, the zirconia calcined body has a displacement point at which the maximum value of the amount of the change ((Δρn+1 / ΔT)-(Δρn / ΔT)) between the ratio Δρn / ΔT of the density change in the n-th section and the ratio Δρn+1 / ΔT of the density change in the (n+1)-th section is at least 0.010 in the temperature range of 1200-1350°C.

Description

Zirconia calcined body

[0001] The present invention relates to a zirconia calcined body. More specifically, the present invention relates to a zirconia calcined body that reaches a relative density of 99.0% or more when subjected to high-speed sintering with a high temperature increase rate of 350°C / min, and that has excellent translucency.

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

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

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

[0005] Since dental prostheses made of zirconia materials have excellent strength and translucency, zirconia sintered bodies have been proposed, for example, in Patent Document 1.

[0006] JP 2010-150064 A

[0007] Patent Document 1 describes a sintering shrinkage rate (Δρ / ΔT: g / cm) in the range of relative density from 70% to 90% when fired at 5°C / min. 3It was disclosed that by setting the temperature (°C) to 0.0120 or more and 0.0135 or less, the density of the finally obtained zirconia sintered body can be improved.

[0008] However, Patent Document 1 does not mention the change in density of the sintered body when the temperature is increased at a rate faster than 5°C / min. Furthermore, the present inventors have found that when the invention of Patent Document 1 is heated at a high rate (350°C / min) and held for a certain period of time, the density of the sintered body does not reach a relative density of 99.0% or more, and translucency is not achieved when fired at 5°C / min. Therefore, it has been found that the invention of Patent Document 1 has room for improvement in order to further reduce the firing time.

[0009] An object of the present invention is to provide a zirconia calcined body that reaches a relative density of 99.0% or more when subjected to high-speed sintering with a high temperature rise rate of 350°C / min, and that has excellent translucency.

[0010] As a result of extensive research to solve the above problems, the inventors of the present invention have found that six types of samples containing zirconia and yttria were prepared by setting six target temperatures from 1150°C to 1400°C in increments of 50°C, raising the temperature from a temperature range of 400°C or less to each of the six different target temperatures at a heating rate of 350°C / min, holding the samples at each target temperature for 10 minutes, and then lowering the temperature to 25°C. The temperature range from 1150°C to 1400°C was divided into sections every 50°C. In this case, the temperature ranges were set at 50°C intervals from 1150°C, and an n-th temperature range (n represents an integer of 1 or more) was set, with the temperature range from 1150°C to 1200°C being the first section and the temperature range from 1200°C to 1250°C being the second section. Using the six types of samples, the change in density between the calcined body at the upper limit temperature and the lower limit temperature in the n-th interval (n is an integer of 1 or more) was calculated as Δρ n When the temperature change amount is ΔT, in the temperature range of 1200°C or more and 1350°C or less, the density change rate Δρ in the nth section is n / ΔT and the rate of density change in the n+1th section Δρ n+1 / ΔT and the change amount ((Δρ n+1 / ΔT)-(Δρ n The present inventors have found that by preparing a zirconia calcined body having a displacement point at which the maximum value of (ΔT) / ΔT) is 0.010 or more, a zirconia sintered body that can be obtained even by high-speed sintering with a high temperature rise rate of 350°C / min has excellent translucency, and have conducted further research based on this finding, which has led to the completion of the present invention.

[0011] The present invention encompasses the following inventions: [1] A method for producing six samples containing zirconia and yttria, wherein six target temperatures are set between 1150°C and 1400°C in increments of 50°C, the temperature is raised from a temperature range of 400°C or less to each of the six different target temperatures at a heating rate of 350°C / min, the sample is held at each target temperature for 10 minutes, and then the temperature is lowered to 25°C, and six samples are produced by dividing the target temperature range from 1150°C to 1400°C into intervals of 50°C each, and using the six samples, the amount of change in density of the calcined body at the upper limit temperature and the lower limit temperature of the nth interval (n is an integer of 1 or more) is calculated as Δρ n When the temperature change amount is ΔT, in the temperature range of 1200°C or more and 1350°C or less, the density change rate Δρ in the nth section is n / ΔT and the rate of density change in the n+1th section Δρ n+1 / ΔT and the change amount ((Δρ n+1 / ΔT)-(Δρ n [2] The zirconia calcined body according to [1], wherein the yttria content is 3.5 mol % or more and 7.5 mol % or less relative to the total moles of zirconia and yttria. [3] The zirconia calcined body according to [1], wherein the density at the temperature (°C) of the calcined body at ... 3 The zirconia calcined body according to [1] or [2] below.

[0012] The zirconia calcined body of the present invention can reach a relative density of 99.0% or more through high-speed sintering with a high temperature rise rate of 350°C / min, and the obtained zirconia sintered body has excellent translucency. Furthermore, the present invention can provide a zirconia calcined body that has excellent translucency even when the holding time at the maximum sintering temperature is 2 minutes.

[0013] [Zirconia calcined body] The zirconia calcined body of the present invention contains zirconia and yttria, and six target temperatures are set from 1150°C to 1400°C in increments of 50°C, and the temperature is raised from a temperature range of 400°C or less to each of the six different target temperatures at a heating rate of 350°C / min, and then the temperature is lowered to 25°C after holding at each target temperature for 10 minutes. When six types of samples are produced, the temperature range of the target temperatures from 1150°C to 1400°C is divided into intervals of 50°C each, and the amount of change in density of the calcined body at the upper limit temperature and the lower limit temperature of the nth interval (n is an integer of 1 or more) is measured using the six types of samples. n When the temperature change amount is ΔT, in the temperature range of 1200°C or more and 1350°C or less, the density change rate Δρ in the nth section is n / ΔT and the rate of density change in the n+1th section Δρ n+1 / ΔT and the change amount ((Δρ n+1 / ΔT)-(Δρ n / ΔT)) has a displacement point at which the maximum value is 0.010 or more.

[0014] As used herein, the term "zirconia composition" refers to a composition containing zirconia powder and a stabilizer powder. As used herein, the term "molded body" refers to a body that has not yet reached either a semi-sintered state (calcined state) or a sintered state. That is, a molded body is distinguished from a calcined body and a sintered body in that it is a body that has been formed by molding and then not yet fired. As used herein, the term "zirconia calcined body" refers to a body that is in a semi-sintered state in which zirconia particles are necked (adhered) to each other and are not completely sintered. As used herein, the term "zirconia sintered body" refers to a body that is in a sintered state in which zirconia particles are completely sintered. In a zirconia sintered body, the zirconia particles solidify together through sintering, and as sintering progresses, the relative density increases and densification progresses, resulting in a completely sintered state in which the relative density is 95% or more. As used herein, "zirconia" refers to zirconium (IV) oxide (ZrO), and ZrO particles contain a trace amount of HfO relative to the amount of ZrO (0.5% by mass to 3% by mass). Because HfO is difficult to separate, terms such as "zirconia," "zirconia particles," and "zirconia powder" refer to materials containing both ZrO and HfO. Furthermore, particles and powders in which a stabilizer is dissolved in zirconia are also included in the terms "zirconia particles" and "zirconia powder," respectively. As used herein, "atmospheric pressure" refers to standard atmospheric pressure (1 atm). As used herein, "theoretical density" refers to a density calculated from the volume of a crystal unit cell and the sum of the masses contained in the unit cell. For example, the theoretical density of 3 mol% yttria-stabilized zirconia is 6.095 g / cm. 3 and 6.052 g / cm for 5.5 mol% yttria-stabilized zirconia. 3 In this specification, the term "transition point" refers to a point at which the difference (amount of change) in the rate of density change between adjacent sections in 50°C intervals in a specific temperature range, which will be described separately, becomes a value other than 0. The temperature at the transition point between the nth section and the n+1th section is expressed as ((Δρ n+1 / ΔT)-(Δρ n / ΔT)) is a value other than 0. In this specification, the upper and lower limits of numerical ranges (temperature range, content of each component, abundance rate of crystalline system, value calculated from components, etc., and each physical property, etc.) can be combined as appropriate.

[0015] The ratio Δρ of density change in the n-th section in the temperature range of 1200°C or more and 1350°C or less n / ΔT and the rate of density change in the n+1th section Δρ n+1 / ΔT and the change amount ((Δρ n+1 / ΔT)-(Δρ n / ΔT)) is preferably 0.010 or more, more preferably 0.011 or more, and even more preferably 0.012 or more, in order to achieve a relative density of 99.0% or more in high-speed sintering with a high temperature rise rate of 350°C / min and to obtain a zirconia sintered body with better translucency. n+1 / ΔT)-(Δρ n / ΔT) is preferably 0.050 or less, more preferably 0.045 or less, and even more preferably 0.040 or less, since a zirconia sintered body having better translucency can be obtained by high-speed firing with a high temperature rise rate of 350° C. / min.

[0016] The method for measuring the density of the calcined body and the method for calculating the change in density are as described in the Examples below.

[0017] The change in the amount ((Δρ n+1 / ΔT)-(Δρ n Although it is unclear why a zirconia sintered body with excellent translucency can be obtained by high-speed sintering with a high temperature rise rate of 350°C / min when the relative density reaches 99.0% or more by setting the change in Δρ / ΔT) within a predetermined range, it is presumed as follows. In high-speed sintering including a high temperature rise rate of 350°C / min (hereinafter also simply referred to as "high-speed sintering"), it is assumed that a sintered body with low relative density has internal pores. The inventors have found that in the high-speed sintering, the change in Δρ / ΔT) within the temperature range of 1200°C or higher and 1350°C or lower is large enough to reduce the change in Δρ / ΔT. n+1 / ΔT)-(Δρ nBy having a transition point where the maximum value of (ΔT / ΔT)) is 0.010 or more, rapid grain growth is suppressed in the temperature range before the transition point, thereby suppressing the incorporation of vacancies in the low-temperature range of 1200°C or higher and 1350°C or lower, and it is believed that when the zirconia raw material undergoes a crystalline phase transition (for example, from monoclinic to tetragonal or cubic), the density difference between the phases promotes the expulsion of voids in the high-temperature range above 1350°C. This is believed to enable a sintered body to reach a relative density of 99.0% or higher even during high-speed sintering and to have excellent translucency.

[0018] In the zirconia calcined body of the present invention, the density of the calcined body at the temperature (°C) of the transition point (the transition point at which the amount of change is maximum) is set to 4.5 g / cm3 in order to further promote the expulsion of voids in the high temperature region. 3 It is preferable that the density is 4.2 g / cm or less. 3 More preferably, it is 4.1 g / cm or less. 3 Furthermore, the density of the calcined body at the transition temperature (°C) is preferably 3.0 g / cm or less, since the relative density reaches 99.0% or more in high-speed firing. 3 It is preferable that the density is 3.1 g / cm or more. 3 More preferably, it is 3.2 g / cm or more. 3 More preferably, it is equal to or greater than this.

[0019] The zirconia calcined body contains yttria (Y2O3) as a stabilizer capable of suppressing the phase transition of zirconia.

[0020] The yttria content in the zirconia calcined body is preferably 2.5 mol% or more, more preferably 3.0 mol% or more, even more preferably 3.5 mol% or more, and particularly preferably 4.0 mol% or more, based on the total moles of zirconia (zirconium (IV) oxide; ZrO2) and stabilizer. A content of 2.5 mol% or more is preferable in that the crystal system contained in the sintered body contains more cubic systems, thereby improving translucency. Furthermore, the content of the stabilizer is preferably 10 mol% or less, more preferably 9.0 mol% or less, even more preferably 8.5 mol% or less, and particularly preferably 8 mol% or less. A content of 10 mol% or less is preferable in that it prevents a decrease in strength.

[0021] The zirconia calcined body of the present invention may contain only yttria as the stabilizer capable of suppressing the phase transition of zirconia, or may further contain a stabilizer other than yttria that is capable of suppressing the phase transition of zirconia. Examples of stabilizers other than yttria that are capable of suppressing the phase transition of zirconia (hereinafter simply referred to as "stabilizers") include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (YO), cerium oxide (CeO), scandium oxide (ScO), niobium oxide (NbO), lanthanum oxide (LaO), erbium oxide (ErO), praseodymium oxide (PrO, PrO), and the like. 11 Examples of the stabilizer include oxides such as samarium oxide (SmO), europium oxide (EuO), thulium oxide (TmO), gallium oxide (GaO), indium oxide (InO), and ytterbium oxide (YbO). One of the stabilizers may be used alone, or two or more of them may be used in combination.

[0022] The zirconia calcined body of the present invention may contain additives other than zirconia and stabilizers, such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (AlO), titanium oxide (TiO), and silica (SiO), as long as the effects of the present invention are achieved.

[0023] Examples of the pigment include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically, NiO, CrO, etc.) (however, YO and CeO are excluded). An oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb is preferred, and an oxide of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb is more preferred. The zirconia calcined body of the present invention may also be free of erbium oxide (Er2O3). Examples of the composite pigment include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4.ZrSiO4, and (Co,Zn)Al2O4. Examples of the fluorescent agent include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl2O4. 10 O 17 : Eu, etc.

[0024] The zirconia calcined body of the present invention may contain a fluorescent agent. By including a fluorescent agent in the zirconia calcined body, the zirconia sintered body has fluorescence. The type of fluorescent agent is not particularly limited, and one or more fluorescent agents capable of emitting fluorescence with light of any wavelength can be used. Examples of fluorescent agents include those containing metal elements. Examples of such metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one of these metal elements alone, or two or more of them. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred. Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the above metal elements. The fluorescent agents are Y2SiO5:Ce, Y2SiO5:Tb, (Y, Gd, Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl.10 O 17 :Eu, etc.

[0025] The content of the fluorescent agent in the zirconia calcined body is not particularly limited and can be adjusted appropriately depending on the type of fluorescent agent or the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the fluorescent agent content is preferably 0.001 mass% or more, more preferably 0.005 mass% or more, and even more preferably 0.01 mass% or more, calculated as the oxide of the metal element contained in the fluorescent agent, relative to 100 mass% of zirconia contained in the zirconia calcined body. Furthermore, the fluorescent agent content is not limited, as long as suitable fluorescence is exhibited, and may be 1 mass% or less, 0.5 mass% or less, or even 0.1 mass% or less. When the content is equal to or greater than the lower limit, the fluorescence is comparable to that of natural human teeth. When the content is equal to or less than the upper limit, the decrease in translucency and mechanical strength can be suppressed.

[0026] The flexural strength of the zirconia calcined body of the present invention is preferably 15 MPa or more to ensure strength that allows mechanical processing in the calcined body state, and is preferably 70 MPa or less, more preferably 60 MPa or less, to facilitate mechanical processing in the calcined body state.

[0027] The bending strength can be measured in accordance with ISO 6872:2015 (Dentistry - Ceramic materials), but the only change is the size of the test specimen, which is measured using a test specimen measuring 5 mm x 10 mm x 50 mm. The test specimen's face and C-face (the surface where the corners of the test specimen are chamfered at a 45° angle) are finished in the longitudinal direction with 600-grit sandpaper. The test specimen is positioned so that the widest surface faces vertically (load direction). In the three-point bending test, the support distance (span) is 30 mm and the crosshead speed is 0.5 mm / min.

[0028] The density of the zirconia calcined body of the present invention is 2.7 g / cm 3More preferably, 3.0 g / cm 3 More preferably, it is 3.2 g / cm or more. 3 It is more preferable that the density of the zirconia calcined body is 4.0 g / cm or more. 3 Preferably, 3.8 g / cm or less 3 More preferably, 3.6 g / cm 3 The following is even more preferable: When the density is within the above range, molding can be easily carried out.

[0029] The density of the zirconia calcined body can be calculated by (mass of the zirconia calcined body) / (volume of the zirconia calcined body). The density of the zirconia calcined body can be calculated, for example, by cutting out 10 mm square specimens (n=3) from arbitrary positions on the zirconia calcined body while changing the cutting position, measuring the mass and volume of the obtained specimens, calculating the arithmetic mean value of the measured values, and using the arithmetic mean value to calculate the density according to the above formula.

[0030] [Method for producing zirconia calcined body] Next, a method for producing a zirconia calcined body will be described. The method for producing a zirconia calcined body is not particularly limited as long as it is a production method that can obtain the desired displacement point. A preferred method for producing a zirconia calcined body comprises pulverizing a zirconia composition, shaping the pulverized zirconia composition into a molded body, and firing (calcining) the molded body to an extent that zirconia particles do not sinter together, and applying excess energy compared to conventional techniques in the pulverization treatment under predetermined conditions, thereby producing the zirconia calcined body of the present invention.

[0031] The zirconia composition can be produced by mixing raw material powders, zirconia powder and yttria powder, using any known method and apparatus without any particular limitations.

[0032] As a method for preparing the zirconia particles constituting the zirconia powder and the yttria particles constituting the yttria powder, for example, a breakdown process in which coarse particles are pulverized or crushed to form fine powder, or a building-up process in which atoms or ions are synthesized through a nucleation and growth process can be employed.

[0033] The zirconia constituting the zirconia powder is not particularly limited, and any of tetragonal zirconia, monoclinic zirconia, and cubic zirconia can be used. In the zirconia powder, these may be used alone or in combination of two or more.

[0034] As the zirconia powder, commercially available zirconia particles may be used, or the commercially available powder may be used after being pulverized in a known pulverizing / mixing device (such as a ball mill).As the yttria powder, commercially available yttria particles may be used, or the commercially available powder may be used after being pulverized in a known pulverizing / mixing device (such as a ball mill).

[0035] Commercially available zirconia powders include, for example, zirconia powders (trade names "Zpex (registered trademark)" (Y2O3 content: 3 mol%), "Zpex (registered trademark) 4" (Y2O3 content: 4 mol%), and "Zpex (registered trademark) Smile (registered trademark)" (YO content: 5.5 mol%), "TZ-3Y" (YO content: 3 mol%), "TZ-3YS" (YO content: 3 mol%), "TZ-4YS" (YO content: 4 mol%), "TZ-6Y" (YO content: 6 mol%), "TZ-6YS" (YO content: 6 mol%), "TZ-8YS" (YO content: 8 mol%), "TZ-10YS" (YO content: 10 mol%), "TZ-3Y-E" (YO content: 3 mol%), "TZ- Examples of such zirconia include "TZ-3YS-E" (YO content: 3 mol%), "TZ-3YB-E" (YO content: 3 mol%), "TZ-3YSB-E" (YO content: 3 mol%), "TZ-3YB" (YO content: 3 mol%), "TZ-3YSB" (YO content: 3 mol%), "TZ-3Y20AB" (YO content: 3 mol%), "TZ-8YSB" (YO content: 8 mol%), and "TZ-0" (YO content: 0 mol%; monoclinic zirconia); all manufactured by Tosoh Corporation.

[0036] Next, the zirconia composition is further pulverized. By subjecting the zirconia composition to a pulverization treatment under predetermined conditions, the desired transition point can be obtained. In the present invention, when a zirconia composition containing zirconia and yttria is subjected to a pulverization treatment under predetermined conditions, the mixing of the zirconia particles and the yttria particles is promoted, resulting in a uniform composition distribution, which limits the temperature range in which the zirconia phase transition occurs, thereby obtaining the desired transition point not seen in conventional products. Rapid grain growth is suppressed in the temperature range before the transition point, thereby suppressing the incorporation of vacancies in the low-temperature range of 1200°C or higher and 1350°C or lower. In the high-temperature range above 1350°C, when the zirconia raw material undergoes a crystalline phase transition (e.g., a phase transition from monoclinic to tetragonal or cubic), the difference in density between the phases promotes the expulsion of voids. It is presumed that excellent translucency can be achieved even when the holding time at the maximum sintering temperature is 2 minutes.

[0037] In the grinding process, it is preferable to use the following methods: (i) grinding media with a diameter of less than 1 mm are used and the grinding time is 10 minutes or more, or (ii) grinding media with a diameter of 1 mm or more are used and the grinding time is more than 40 hours.

[0038] When using grinding media with a diameter of less than 1 mm, the diameter of the grinding media is preferably 0.1 to 0.5 mm, since the desired displacement point is easily obtained by using grinding media with a fine diameter. Commercially available grinding media with a diameter of less than 1 mm may be used. Examples of grinding devices that use grinding media with a diameter of less than 1 mm include bead mills.

[0039] When using grinding media with a diameter of less than 1 mm, the grinding time is not particularly limited, but is preferably 10 minutes or more, more preferably 12 minutes or more, even more preferably 15 minutes or more, and particularly preferably 20 minutes or more, because yttria particles can be easily ground to very small sizes. The grinding time is preferably 20 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and particularly preferably 2 hours or less. When using a grinding device that grinds while circulating the slurry (e.g., a bead mill), the grinding time refers to the residence time of the slurry in the vessel (grinding chamber).

[0040] When using grinding media with a diameter of 1 mm or more, the grinding media diameter (diameter) is preferably 1.5 mm or more, and more preferably 2.0 mm or more, because this makes it easier to increase the amount of energy required for the grinding process by increasing the grinding time. Commercially available grinding media with a diameter of 1 mm or more may be used. Examples of grinding devices that use grinding media with a diameter of 1 mm or more include ball mills.

[0041] When using grinding media with a diameter of 1 mm or more, the grinding time (grinding treatment time) is not particularly limited, but is preferably more than 40 hours, more preferably 55 hours or more, and is even more preferably 80 hours or more, particularly preferably 100 hours or more, because the mixing of zirconia particles and yttria particles is promoted by applying an excess amount of energy compared to conventional techniques when grinding the zirconia composition, resulting in a uniform composition distribution and making it easier to obtain the desired transition point. Furthermore, the grinding treatment time is preferably 1,000 hours or less, more preferably 800 hours or less, even more preferably 500 hours or less, and particularly preferably 300 hours or less.

[0042] The zirconia composition may be in the form of granules, a slurry, etc. When the zirconia composition is in the form of a slurry, the slurry can be produced by mixing the mixed powder obtained by the pulverization treatment with a solvent (preferably water).

[0043] The average particle size of the zirconia composition after the pulverization treatment is preferably 0.2 μm or less, in order to provide a sintered body with excellent mechanical strength and translucency.

[0044] The average particle sizes of the zirconia particles and the yttria particles can be measured by a dynamic light scattering particle size distribution measurement method, for example, using a dynamic light scattering particle size distribution measurement device (product name "SZ-100V2") manufactured by Horiba, Ltd. A slurry diluted to about 0.1 mass % with water is irradiated with ultrasonic waves for 30 minutes, and then the average particle sizes can be measured on a volume basis while applying ultrasonic waves.

[0045] The zirconia composition may also contain additives such as binders, dispersants, emulsifiers, antifoaming agents, pH adjusters, lubricants, and light transmittance adjusters. The additives may be used alone or in combination of two or more. Examples of binders include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic binders, wax binders, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.

[0046] In order to improve translucency, the content of the binder in the zirconia composition of the present invention is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less, relative to 100% by mass of zirconia.

[0047] Examples of the plasticizer include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0048] Examples of dispersants include ammonium polycarboxylate (e.g., triammonium citrate), ammonium polyacrylate, acrylic copolymer resin, acrylic acid ester copolymer, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (e.g., polyoxyethylene alkyl ether phosphate esters such as polyoxyethylene lauryl ether phosphate esters), nonionic surfactants, olein glyceride, amine salt surfactants, oligosaccharide alcohols, and stearic acid.

[0049] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitan derivatives.

[0050] Examples of the antifoaming agent include alcohol, polyether, polyethylene glycol, silicone, and wax.

[0051] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxides such as tetramethylammonium hydroxide).

[0052] Examples of the lubricant include polyoxyethylene alkyl ether and wax.

[0053] Examples of the light transmittance adjusting agent include aluminum oxide (Al2O3), titanium oxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0054] The BET specific surface area of ​​the particles constituting the zirconia composition is 7.0 m when measured in accordance with JIS Z 8830:2013. 2 / g or more, and 7.5m 2 / g or more, and more preferably 8.0m 2 / g or more is more preferable. 2 / g or more, the sintered body can be prevented from becoming cloudy when sintered. 2 / g or less, and 2 / g or less is more preferable, and 40m 2 / g or less is more preferable. 2 / g or less, the BET specific surface area is less susceptible to temperature variations in the firing furnace. The BET specific surface area can be measured using a commercially available product such as a fully automatic specific surface area measuring device (trade name "Macsorb (registered trademark) HM model-1200", BET flow method (single-point method / multi-point method), manufactured by Mountec Co., Ltd.). For example, it can be measured by the BET flow method (single-point method) using the fully automatic specific surface area measuring device. Furthermore, even when the firing time for sintering is shortened, the light transmittance of the sintered body is less likely to decrease. The "BET specific surface area" referred to here is a specific surface area measured without distinguishing between primary particles and secondary particles.

[0055] Next, the pulverized zirconia composition is subjected to a molding step to produce a molded body, which is obtained by applying an external force to the zirconia composition using a known method.

[0056] The molding method is not particularly limited, and the following methods can be used, for example: (a) a step of slip-casting a slurry containing the pulverized zirconia composition; (b) a step of gel-casting a slurry containing the pulverized zirconia composition; (c) a step of press-molding the pulverized zirconia composition; (d) a step of molding a zirconia composition containing zirconia particles, yttria particles, and a resin; (e) a step of polymerizing a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer; and (f) a step of additive manufacturing of granules containing zirconia particles and yttria particles.

[0057] (a) Slip Casting When a zirconia molded body is produced by a method including a step of slip-casting a slurry containing a zirconia composition after a pulverization treatment, the specific slip-casting method is not particularly limited. For example, a method in which the slurry is poured into a mold and then dried can be employed. The content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, because this facilitates pouring the slurry into the mold, prevents the drying process from taking a long time, and allows the mold to be used more frequently. The slurry may be poured into the mold under normal pressure, but from the viewpoint of production efficiency, it is preferable to pour the slurry into the mold under pressurized conditions.

[0058] (b) Gel Casting When a zirconia molded body is produced by a method including a step of gel-casting a slurry containing a zirconia composition after a pulverization treatment, the specific gel-casting method is not particularly limited. For example, a method can be employed in which the slurry is gelled in a mold to obtain a shaped wet body, and then this is dried. The content of the dispersion medium in the slurry used is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, in order to prevent a long drying time and to suppress the occurrence of cracks during drying. Gelation can be carried out, for example, by adding a gelling agent or by adding a polymerizable monomer and then polymerizing it.

[0059] There is no limitation on the type of gelling agent, and for example, a water-soluble gelling agent can be used, and specifically, agarose, gelatin, etc. can be preferably used. A single gelling agent may be used alone, or two or more types may be used in combination. The amount of gelling agent used is not particularly limited as long as problems such as cracking do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less based on the mass of the slurry after the gelling agent is blended.

[0060] The type of polymerizable monomer is not particularly limited, and examples thereof include (meth)acrylate monomers such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; and (meth)acrylamide monomers such as N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N,N-bis(2-hydroxyethyl) (meth)acrylamide. One type of polymerizable monomer may be used alone, or two or more types may be used in combination. The amount of polymerizable monomer used is not particularly limited as long as problems such as cracking do not occur during sintering, but can be 10% by mass or less, 5% by mass or less, or 1% by mass or less, based on the mass of the slurry after the polymerizable monomer is blended.

[0061] When gelation is carried out by polymerization of a polymerizable monomer, the polymerization is preferably carried out using a polymerization initiator. There are no particular restrictions on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred.

[0062] Specific examples of the photopolymerization initiator include (bis)acylphosphine oxides (including salts), thioxanthones (including salts such as quaternary ammonium salts), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ether compounds, and α-aminoketone compounds. One photopolymerization initiator may be used alone, or two or more may be used in combination. Among these photopolymerization initiators, it is preferable to use at least one selected from the group consisting of (bis)acylphosphine oxides and α-diketones. This allows polymerization (gelation) to occur in both the ultraviolet (including near-ultraviolet) and visible light regions, and in particular, polymerization (gelation) can be sufficiently performed using any light source, such as a laser (e.g., Ar laser, He—Cd laser), or lighting (e.g., halogen lamp, xenon lamp, metal halide lamp, light-emitting diode (LED), mercury lamp, or fluorescent lamp.

[0063] The drying method for drying the shaped wet body is not particularly limited, and examples thereof include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. These may be used alone or in combination. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred because they can suppress the occurrence of cracks during drying.

[0064] There are no particular limitations on the type of mold used in slip casting and gel casting, and for example, porous molds made of plaster, resin, ceramics, etc., and non-porous molds made of metal, resin, etc. can be used.

[0065] (c) Press Molding In the step of press molding the zirconia composition after the pulverization treatment, the specific method of press molding is not particularly limited, and can be performed using a known press molding machine. Specific examples of the press molding method include uniaxial pressing.

[0066] Alternatively, multi-stage molding may be performed. For example, after press-molding the zirconia composition, a cold isostatic pressing (CIP) treatment may be further performed.

[0067] The shape of the molded body is not particularly limited and may be a disk, a rectangular parallelepiped, or a dental product shape (e.g., a crown shape). The molded body may be, for example, a columnar zirconia molded body obtained by filling a mold with a zirconia composition (e.g., granules) and compacting it with a uniaxial press. The higher the surface pressure in the press molding, the higher the density of the molded body. On the other hand, if the density of the zirconia molded body is too high, the zirconia calcined body will become hard. Therefore, the surface pressure in the press molding when producing the zirconia molded body is preferably 30 to 200 MPa. When the surface pressure in the press is 30 MPa or more, the shape retention of the zirconia molded body is excellent, and when it is 200 MPa or less, the density of the zirconia molded body does not increase too much, making it easier to prevent hardening.

[0068] The molded body also includes a molded body densified by a high-temperature pressure treatment such as CIP (Cold Isostatic Pressing). From the same viewpoint as above, the pressure of the CIP is preferably 30 to 200 MPa.

[0069] (d) Molding of a zirconia composition containing a resin When a zirconia molded body is produced by a method including a step of molding a zirconia composition containing zirconia particles, yttria particles, and a resin, the specific method for molding the zirconia composition is not particularly limited, and for example, injection molding, cast molding, extrusion molding, etc. can be used. Furthermore, a method of molding the composition by fusion dynamic molding (FDM), an inkjet method, a powder / binder lamination method, or other additive manufacturing methods (3D printing, etc.) may also be used. Among these molding methods, injection molding and cast molding are preferred, and injection molding is more preferred. The type of resin is not particularly limited, and it is preferable to use the binder described above.

[0070] (e) Polymerization of a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer. Polymerization of a zirconia composition containing zirconia particles, yttria particles, and a polymerizable monomer or oligomer polymerizes the polymerizable monomer or oligomer in the composition, thereby hardening the composition. When producing a zirconia molded body using a method including this polymerization step, the specific method is not particularly limited. For example, a method of polymerizing a zirconia composition in a mold or a stereolithography (SLA) method using a zirconia composition can be employed. Among these, the stereolithography (SLA) method (b) is preferred. Stereolithography allows the zirconia molded body to be given a shape corresponding to the desired shape of the final zirconia sintered body at the time of production. Therefore, stereolithography may be particularly suitable when the zirconia sintered body is used as a dental material for dental prostheses, etc. The type of polymerizable monomer is not particularly limited, and may be any of monofunctional polymerizable monomers such as monofunctional (meth)acrylates and monofunctional (meth)acrylamides, and polyfunctional polymerizable monomers such as bifunctional aromatic compounds, bifunctional aliphatic compounds, and trifunctional or higher compounds. One type of polymerizable monomer may be used alone, or two or more types may be used. Among these, it is preferable to use a polyfunctional polymerizable monomer, particularly when a stereolithography method is employed. The oligomer is not particularly limited as long as it is a compound in which two or more of the above polymerizable monomers are bonded and has polymerizability.

[0071] Examples of monofunctional (meth)acrylates include (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and sec-butyl (meth)acrylate. alkyl (meth)acrylates such as acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate; alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic group-containing (meth)acrylates such as benzyl (meth)acrylate and phenyl (meth)acrylate; and (meth)acrylates having a functional group such as 2,3-dibromopropyl (meth)acrylate, 3-(meth)acryloyloxypropyltrimethoxysilane, and 11-(meth)acryloyloxyundecyltrimethoxysilane. Examples of monofunctional (meth)acrylamides include (meth)acrylamide, N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-di-n-propyl(meth)acrylamide, N,N-di-n-butyl(meth)acrylamide, N,N-di-n-hexyl(meth)acrylamide, N,N-di-n-octyl(meth)acrylamide, N,N-di-2-ethylhexyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and N,N-bis(2-hydroxyethyl)(meth)acrylamide.Among these monofunctional polymerizable monomers, (meth)acrylamide is preferred because of its excellent polymerizability, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.

[0072] Examples of the bifunctional aromatic compound include 2,2-bis((meth)acryloyloxyphenyl)propane, 2,2-bis[4-(2-hydroxy-3-acryloyloxy-2-hydroxypropoxy)phenyl]propane, 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (commonly known as "Bis-GMA"), 2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane, 2, Examples of (meth)acrylates include 2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane, 2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, and 1,4-bis(2-(meth)acryloyloxyethyl)pyromellitate. Among these, Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article. Of the 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propanes, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average number of moles of ethoxy groups added: 2.6, commonly known as "D-2.6E") is preferred.

[0073] Examples of the bifunctional aliphatic compounds include glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of (meth)acrylates include triethylene glycol dimethacrylate (TEGDMA) and UDMA, which are preferred because of their excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0074] Examples of tri- or higher functional compounds include (meth)acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacryloyloxy-2,2,6,6-tetra(meth)acryloyloxymethyl-4-oxaheptane. Among these, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetramethacrylate and 1,7-diacryloyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxaheptane are preferred in terms of excellent polymerizability and the mechanical strength of the resulting zirconia molded article.

[0075] In any of the above methods, the polymerization of the composition is preferably carried out using a polymerization initiator, and the composition preferably further contains a polymerization initiator. There are no particular limitations on the type of polymerization initiator, but a photopolymerization initiator is particularly preferred. The photopolymerization initiator can be appropriately selected from photopolymerization initiators used in general industry, and photopolymerization initiators used in dental applications are particularly preferred. Specific examples of photopolymerization initiators are the same as those described above in the explanation of gel casting.

[0076] When a zirconia molded body is produced by stereolithography using a zirconia composition, the specific method of stereolithography is not particularly limited, and any known method can be appropriately employed for stereolithography. For example, a method can be employed in which a liquid composition is photopolymerized using an optical shaping device with ultraviolet light, a laser, or the like to sequentially form layers having a desired shape, thereby obtaining the desired zirconia molded body.

[0077] To further improve the density of the cured zirconia molded body, the zirconia molded body may be subjected to a humidification treatment followed by a CIP treatment. When press molding is performed, a powder containing zirconia particles may be humidified before press molding, followed by press molding. The humidification method may be any known method, including spraying water with a spray bottle or using a hygrostat or thermo-hygrostat. The moisture content of the humidification treatment varies depending on the average particle size of the zirconia particles and the average particle size of the stabilizer particles, but is preferably greater than 2% by mass, more preferably greater than 3% by mass, even more preferably greater than 4% by mass, and particularly preferably greater than 5% by mass, relative to the mass of the powder before humidification (powder before humidification treatment) and the molded body. It is also preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 11% by mass or less. The moisture content of the powder after humidification can be calculated as a percentage by subtracting the mass of the powder before humidification and the compact from the mass of the wet powder (powder after humidification) and the compact, and dividing the result by the mass of the powder before humidification and the compact. The pressure for the CIP treatment is the same as that described above in the description of press molding.

[0078] (f) Step of additive manufacturing of granules containing zirconia particles and yttria particles When manufacturing granules containing zirconia particles and yttria particles, there are no particular limitations on the specific method. For example, a method can be used in which the granules are slurried and then dried in a spray dryer to form granules, and the resulting granules can be used for powder additive manufacturing. There are no particular limitations on the powder additive manufacturing method, but examples include a powder bed method, an SLS method (selective laser sintering method), an SLM method (selective laser melting method), an electron beam method, an arc discharge method, and a binder jet method. For methods in which it is preferable to not use organic substances during additive manufacturing, it is preferable not to use organic substances even in the granule manufacturing stage.

[0079] Next, the compact is calcined in a calcination step to obtain the calcined zirconia body of the present invention.

[0080] The calcination temperature (maximum calcination temperature) in the calcination step is preferably 800°C or higher, more preferably 850°C or higher, even more preferably 900°C or higher, and particularly preferably 950°C or higher, from the viewpoint of ensuring a semi-sintered state using the above-mentioned specific zirconia composition. Furthermore, the calcination temperature is preferably 1200°C or lower, more preferably 1150°C or lower, even more preferably 1100°C or lower, and particularly preferably 1050°C or lower, from the viewpoint of ensuring workability. That is, the calcination temperature is preferably 800°C to 1200°C in the method for producing a zirconia calcined body of the present invention.

[0081] The holding time (holding time) at the maximum calcination temperature is preferably 30 minutes to 6 hours, allowing the zirconia molded body to reach a semi-sintered state. The heating rate to the maximum calcination temperature and the cooling rate from the maximum calcination temperature are preferably 300°C / min or less. In a preferred embodiment, the heating rate to the maximum calcination temperature when calcining the zirconia molded body of the present invention is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more. It is also preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. Having a heating rate equal to or greater than the lower limit improves productivity. Having a heating rate equal to or less than the upper limit can suppress the volume difference between the interior and exterior of the zirconia molded body or the zirconia calcined body. Furthermore, if the zirconia molded body contains an organic substance, rapid decomposition of the organic substance can be suppressed, thereby suppressing cracking and fracture.

[0082] [Zirconia Sintered Body] Next, the zirconia sintered body will be described. The zirconia sintered body is obtained by firing the zirconia calcined body obtained as described above.

[0083] The content of the stabilizer (yttria and stabilizers other than yttria) in the zirconia sintered body of the present invention is the same as the content of the stabilizer in the zirconia calcined body.

[0084] The zirconia sintered body of the present invention may contain a fluorescent agent. The fluorescent agent is the same as the fluorescent agent in the zirconia calcined body. In this specification, regarding the fluorescent agent, "relative to 100% by mass of zirconia contained in the zirconia calcined body" can be read as "relative to 100% by mass of zirconia contained in the zirconia sintered body."

[0085] The zirconia sintered body of the present invention may contain a colorant. Examples of colorants include those similar to those in the zirconia calcined body. The content of the colorant in the zirconia sintered body is not particularly limited and can be adjusted appropriately depending on the type of colorant and the application of the zirconia sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the content of the colorant, calculated as the oxide of the metal element contained in the colorant, relative to 100% by mass of zirconia contained in the zirconia sintered body, is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more. Furthermore, the content of the colorant, calculated as the oxide of the metal element contained in the colorant, is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and may even be 0.1% by mass or less, or even 0.05% by mass or less.

[0086] In order to adjust the translucency of the zirconia sintered body of the present invention, the zirconia sintered body of the present invention may contain a translucency adjuster. Examples of the translucency adjuster include the same ones as the translucency adjuster in the zirconia calcined body. The content of the translucency adjuster in the zirconia sintered body is not particularly limited and can be appropriately adjusted depending on the type of translucency adjuster and the application of the zirconia sintered body, but from the viewpoint of being preferably usable as a dental prosthesis, the content is preferably 0.1 mass% or less relative to 100 mass% of zirconia contained in the zirconia sintered body.

[0087] The relative density of the zirconia sintered body is preferably 99.0% or more, more preferably 99.2% or more, and even more preferably 99.5% or more. The relative density can be calculated as the ratio of the actual density measured by Archimedes' method to the theoretical density.

[0088] The density of the zirconia sintered body is set to 5.80 g / cm because the higher the density, the fewer internal voids there are and the less light scattering there is, which improves the translucency. 3 It is preferable that the density is 5.82 g / cm or more. 3 More preferably, it is 5.87 g / cm or more. 3 It is more preferable that the zirconia sintered body contains substantially no voids.

[0089] The content of zirconia and stabilizer in the zirconia sintered body is the same as the content in the composition before the sintered body is produced and / or in the calcined body.

[0090] The strength of the zirconia sintered body is preferably higher. For example, the biaxial bending strength is preferably 800 MPa or more, more preferably 820 MPa or more, and even more preferably 840 MPa or more. The biaxial bending strength can be measured in accordance with ISO 6872:2015.

[0091] [Method for producing zirconia sintered body] Examples of methods for producing the zirconia sintered body of the present invention include methods for producing a zirconia sintered body by firing the above-mentioned zirconia calcined body. A preferred method includes a step of firing the above-mentioned zirconia calcined body at 1350°C or higher and 1700°C or lower under atmospheric pressure. This method can easily produce the zirconia sintered body of the present invention, which achieves a relative density of 99.0% or higher even during high-speed firing and has excellent translucency. Furthermore, the method for producing the present invention can easily produce a zirconia sintered body that has excellent translucency even after short-time sintering, such as a holding time of 10 minutes or less (e.g., 2 minutes) at the maximum sintering temperature.

[0092] When the zirconia calcined body of the present invention is fired to produce a sintered body, the maximum sintering temperature is preferably set under conditions that maximize the translucency of the zirconia sintered body. From the viewpoint of easily obtaining the desired zirconia sintered body under normal pressure, the maximum sintering temperature is preferably above 1200°C, more preferably 1250°C or higher, and even more preferably 1300°C or higher. Furthermore, the maximum sintering temperature is preferably 1700°C or lower, more preferably 1650°C or lower, and even more preferably 1600°C or lower. By setting the maximum sintering temperature at or above the above lower limit and below the above upper limit, sintering can proceed sufficiently, making it easy to obtain a dense sintered body. Furthermore, by setting the maximum sintering temperature below the above upper limit, deactivation of the fluorescent agent can be suppressed.

[0093] When producing a sintered body, there is no particular limitation on the holding time at the maximum sintering temperature, but in order to be able to efficiently and stably obtain the target zirconia sintered body with good productivity, the holding time at the maximum sintering temperature is preferably 10 minutes or less, more preferably 5 minutes or less, even more preferably 3 minutes or less, and particularly preferably 2 minutes or less. The holding time is preferably 30 seconds or more, more preferably 45 seconds or more, and even more preferably 1 minute or more.

[0094] The temperature drop rate in the firing step is preferably set so as to shorten the time required for the firing step. For example, the temperature rise rate can be set so as to reach the maximum sintering temperature in the shortest time depending on the performance of the firing furnace. The temperature drop rate from the maximum sintering temperature 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.

[0095] The calcination and firing in the present invention can be carried out using a firing furnace. There are no particular limitations on the type of firing furnace, and for example, electric furnaces and degreasing furnaces commonly used in industry can be used. A commercially available dental firing furnace (for example, the trade name "Sintra CS" (manufactured by Shenpaz)) can also be used.

[0096] The zirconia sintered body of the present invention can be produced without HIP treatment, but by optionally performing HIP treatment after sintering under normal pressure, it is possible to further improve translucency and mechanical strength. Hereinafter, the sintered body obtained by sintering at the above-mentioned maximum sintering temperature (the sintered body before HIP treatment) will be referred to as the "primary sintered body," and the sintered body after HIP treatment will be referred to as the "HIP-treated sintered body." HIP treatment can be performed using a known hot isostatic pressing (HIP) device.

[0097] When the primary sintered body is subjected to HIP treatment, the HIP pressure is not particularly limited, and since a dense sintered body with high strength can be obtained, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more. The upper limit of the HIP pressure is not particularly limited, but can be, for example, 400 MPa or less, 300 MPa or less, or even 200 MPa or less.

[0098] When the primary sintered body is subjected to HIP treatment, the temperature rise rate is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, and even more preferably 0.5°C / min or more. The temperature rise rate is preferably 50°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less. By setting the temperature rise rate at or above the lower limit, productivity is improved.

[0099] When the primary sintered body is subjected to the HIP treatment, the HIP time (the time during which the maximum pressure and temperature are maintained) is not particularly limited, and since a dense zirconia sintered body with high strength can be obtained, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Moreover, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0100] In the method for producing a zirconia sintered body of the present invention, the pressure medium used in HIPing the primary sintered body is not particularly limited. From the viewpoint of minimizing the effect on zirconia, the pressure medium can be at least one selected from the group consisting of oxygen, oxygen containing 3% hydrogen, air, and an inert gas (e.g., nitrogen, argon, etc.). When the primary sintered body is HIPed in an oxygen-mixed gas atmosphere, the oxygen concentration is not particularly limited, but can be, for example, more than 0% and 20% or less. When an oxygen-mixed gas is used, at least one inert gas (e.g., nitrogen, argon, etc.) can be selected as the gas other than oxygen.

[0101] If the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, black discoloration may occur due to oxygen defects. In this case, to remove the black discoloration, it is preferable to include a heat treatment step (hereinafter also referred to as a "tempering treatment") in the air or in an oxygen-excess atmosphere at 1650°C or less after the HIP treatment. From the viewpoint of efficient heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere. An oxygen-excess atmosphere means that the oxygen concentration is higher than that of the air. The oxygen-excess atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and 100% or less, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%. If the HIP treatment is performed in a reducing atmosphere, such as using an inert gas, black discoloration may occur due to oxygen defects. In this case, to remove the black discoloration, it is preferable to include a heat treatment step (hereinafter also referred to as a "tempering treatment") in the air or in an oxygen-excess atmosphere at 1650°C or less after the HIP treatment. From the viewpoint of efficient heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere. An oxygen-excess atmosphere means that the oxygen concentration is higher than that of the air. The oxygen-excess atmosphere is not particularly limited as long as the oxygen concentration is more than 21% and not more than 100%, and can be appropriately selected from this range. For example, the oxygen concentration may be 100%.

[0102] The zirconia sintered body of the present invention is not particularly limited as long as it exhibits the effects of the present invention, and may be a primary sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment.

[0103] The temperature of the heat treatment in the air or in an oxygen-excess atmosphere can be appropriately changed depending on the aesthetics of the zirconia sintered body (e.g., the shade of a dental prosthesis). In a preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1650°C or less, more preferably 1600°C or less, and even more preferably 1550°C or less, from the viewpoint of the aesthetics of the zirconia sintered body. In another preferred embodiment, the temperature of the heat treatment in the air or in an oxygen-excess atmosphere is preferably 1400°C or less, more preferably 1300°C or less, and even more preferably 1200°C or less, from the viewpoint of the aesthetics of the zirconia sintered body. Furthermore, in any embodiment, the temperature of the heat treatment is preferably 500°C or more, more preferably 600°C or more, and even more preferably 700°C or more.

[0104] A general dental zirconia firing furnace can be used for the tempering treatment. Commercially available dental zirconia firing furnaces may be used. Examples of commercially available dental zirconia firing furnaces include Noritake Katana (registered trademark) F-1, F-1N, and F-2 (all manufactured by SK Medical Electronics Co., Ltd.).

[0105] The zirconia sintered body obtained by firing the zirconia calcined body of the present invention can be suitably used for dental products. Examples of dental products include copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, orthodontic wires, and laminate veneers. By using the zirconia calcined body of the present invention for parts such as implant screws and implant fixtures, discoloration of the gums caused by metal materials can be suppressed, resulting in excellent aesthetics. Furthermore, while an appropriate method for manufacturing these products can be selected depending on the application, for example, dental products can be obtained by cutting the zirconia calcined body of the present invention and then firing it. It is preferable to use a CAD / CAM system for the cutting process. The CAD / CAM system is not particularly limited, and known devices can be used. Examples of known devices include a CAD / CAM system ("Katana (registered trademark) CAD / CAM System," manufactured by Kuraray Noritake Dental Co., Ltd.).

[0106] The present invention includes embodiments in which all or part of the above-described configurations are combined in various ways within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved.

[0107] Next, the present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way, and many modifications within the technical scope of the present invention are possible by those skilled in the art.

[0108] [Example 1] Commercially available zirconia powder (YO: 0 mol%) and commercially available yttria powder were added to water, and then placed in a ball mill along with zirconia grinding media (diameter: 2 mm). The mixture was milled for 96 hours in a ball mill to obtain a slurry (average particle size: 0.2 μm or less).

[0109] Next, an organic binder was added to the obtained slurry, and the mixture was mixed and stirred. The stirred slurry was dried and granulated using a spray dryer to obtain a powder. This powder was poured into a cylindrical mold and uniaxially pressed at a pressure of 200 MPa to obtain a compact. The obtained compact was placed in an electric furnace, heated from room temperature at a rate of 10°C / min, and held at 500°C for 2 hours to degrease the organic components. Thereafter, the temperature was raised at a rate of 10°C / min, held at 955°C for 2 hours, and slowly cooled at a rate of -10°C / min to obtain a zirconia calcined body.

[0110] [Example 2 and Comparative Examples 1 and 2] A zirconia calcined body was produced in the same manner as in Example 1, except that the conditions were changed as shown in Table 1. In Example 2 and Comparative Examples 1 and 2, the same yttria raw material as in Example 1 was used.

[0111] In the table, the yttria content refers to the ratio (mol %) of the number of moles of yttria to the total number of moles of zirconia and yttria. In the table, "-" means that no pulverization treatment was performed. The yttria content refers to the value in the slurry, compact, calcined body, and sintered body. In the table, the commercially available product in Comparative Example 1 is a product manufactured by Tosoh Corporation (product name "Zpex").

[0112] <Method of measuring density and method of calculating rate of density change when producing zirconia sintered body> The zirconia calcined bodies of Examples 1 and 2 and Comparative Examples 1 and 2 were pulverized under the conditions shown in Table 1 and formed into a disk shape with a diameter of approximately 18 mm and a thickness of approximately 1.2 mm to obtain a compact. The compact was held at a maximum calcination temperature of 1000°C for 2 hours and slowly cooled at a rate of -0.4°C / min to obtain a zirconia calcined body.

[0113] Six target temperatures were set at 50°C intervals from 1150°C to 1400°C, and the zirconia calcined bodies of each example and comparative example were heated to each target temperature at theoretical density in a dental firing furnace (product name "Sintra CS" (manufactured by Shenpaz)) from room temperature. The bodies were then held at the target temperature for 10 minutes and cooled to 25°C to obtain six samples (zirconia sintered bodies) with different target temperatures (maximum sintering temperatures). The temperature drop was set to -200°C / min up to 950°C, after which the firing furnace was opened and the body was allowed to cool. All samples were subjected to the same temperature drop treatment. The mass of the obtained zirconia sintered bodies was measured using an electronic balance, and the thickness and diameter of each sample were accurately measured using a micrometer. The mass was then measured using a precision balance, and the formula (mass of the calcined body) / (volume of the calcined body) was calculated (arithmetic average of n = 3). The temperature range of the target temperature from 1150°C to 1400°C was divided into intervals of 50°C each, and the six samples were used to calculate the change in density of the calcined body at the upper limit temperature and the lower limit temperature of the nth interval (n is an integer of 1 or more). n When the temperature change amount is ΔT, in the temperature range of 1200°C or more and 1350°C or less, the density change rate Δρ in the nth section is n / ΔT and the rate of density change in the n+1th section Δρ n+1 The change in ΔT was calculated. The results are shown in Table 2.

[0114] In the table, the unit of density is g / cm 3 Represents.

[0115] <Evaluation of Translucency of Zirconia Sintered Body (Measurement of ΔL*(W−B))> The zirconia calcined bodies of each Example and Comparative Example were subjected to short-term firing in a dental firing furnace (trade name "Sintar CS" (manufactured by Shenpaz)) at a heating rate of 350°C / min at 1580°C for 2 minutes. Each of the obtained zirconia sintered bodies was polished into a flat plate sample with a thickness of 1.0 mm, which was used as a sample for measuring translucency. The translucency of the sample was measured using a spectrophotometer (trade name "Crystal Eye") manufactured by Olympus Corporation, using a 7-band LED light source in measurement mode. Specifically, the translucency of a zirconia sintered body, which is a flat sample, was measured by measuring the lightness (LW*) when the chromaticity was measured against a white background, and by measuring the lightness (LB*) when the chromaticity was measured against a black background using the same sample, the same measuring device, the same measuring mode, and the same light source. The difference between the two (ΔL* = (LW*) - (LB*)) was defined as the translucency (ΔL*(W-B)) (arithmetic mean of n = 3). The L* value is the L* value of the chromaticity (color space) in the L*a*b* color system (JIS Z 8781-4:2013). A translucency ΔL*(W-B) of 13 or more for a sintered body was considered acceptable. The results are shown in Table 1.

[0116] <Method for calculating the relative density of zirconia sintered body> The zirconia calcined bodies of each Example and Comparative Example were subjected to short-term firing in a dental firing furnace (product name "Sintar CS" (manufactured by Shenpaz)) at a heating rate of 350°C / min at 1580°C for 2 minutes. Each of the obtained zirconia sintered bodies was polished into a flat plate sample with a thickness of 1.0 mm to serve as a density measurement sample, and the actual density was measured by the Archimedes method. The relative density was calculated as the ratio of the actual density measured by the Archimedes method to the theoretical density. The results are shown in Table 1.

[0117] As described above, by using the zirconia calcined body of the present invention, a zirconia sintered body having a relative density of 99.0% or more and excellent translucency was obtained through high-speed sintering with a high temperature rise rate of 350°C / min. In the comparative examples, a zirconia sintered body having a theoretical density and excellent translucency could not be obtained.

[0118] The zirconia calcined body of the present invention is useful for producing dental products for treatment in dental clinics.

Claims

1. A method for producing a material containing zirconia and yttria, comprising: setting six target temperatures from 1150°C to 1400°C at intervals of 50°C; heating the material from a temperature range of 400°C or less to the six different target temperatures at a heating rate of 350°C / min; holding the material at each target temperature for 10 minutes; and then lowering the temperature to 25°C to produce six types of samples; dividing the temperature range of target temperatures from 1150°C to 1400°C into intervals at 50°C intervals; and using the six types of samples, measuring the change in density between the calcined body at the upper limit temperature and the lower limit temperature in the nth interval (n is an integer of 1 or more) by Δρ n When the temperature change amount is ΔT, the ratio of density change in the nth section in the temperature range of 1200° C. to 1350° C. is Δρ n / ΔT and the rate of density change in the n+1th section Δρ n+1 / ΔT and the change ((Δρ n+1 / ΔT)-(Δρ n The zirconia calcined body has a displacement point at which the maximum value of (ΔT) is 0.010 or more.

2. The zirconia calcined body according to claim 1, wherein the content of yttria is 3.5 mol % or more and 7.5 mol % or less based on the total moles of zirconia and yttria.

3. The density at the transition point temperature (°C) is 4.5 g / cm 3 The zirconia calcined body according to claim 1 or 2, wherein:

Images