Zirconium oxide presintered body

Abstract

Provided is a zirconia pre-sintered body having a relative density of 99.0% or more during high-speed calcination by high-speed temperature rise at 350 DEG C / min, and the resulting zirconia sintered body having excellent light transmittance. The present invention relates to a zirconia pre-sintered body containing zirconia and yttrium oxide, which comprises six target temperatures per 50 DEG C from 1150 DEG C to 1400 DEG C, is heated from 400 DEG C or less to six different target temperatures at a heating rate of 350 DEG C / min, then stays for 10 minutes at each of the target temperatures, and then is cooled to 25 DEG C, and when six types of samples are prepared, the zirconia pre-sintered body is obtained. A temperature range of a target temperature of 1150 DEG C to 1400 DEG C is divided into sections per 50 DEG C, and when the six types of samples are used, the amount of change in the density of the presintered body at the upper limit temperature and the density of the presintered body at the lower limit temperature in the nth section (n represents an integer of 1 or more) is set as [Delta] [Rhon] n and the amount of change in the temperature is set as [Delta] T, the density of the presintered body is measured in a temperature range of 1200 DEG C to 1350 DEG C (inclusive). And a displacement point at which the maximum value of the amount of change (([delta] [rhon + 1] / [delta] T)-([delta] [rhon / [delta] T)) between the ratio [delta] [rhon / [delta] T of the density change in the n-th section and the ratio [delta] [rhon + 1 / [delta] T of the density change in the (n + 1)-th section is 0.010 or more.

Description

Technical Field

[0001] This invention relates to zirconia pre-sintered bodies. More specifically, this invention relates to zirconia pre-sintered bodies that achieve a relative density of 99.0% or higher through high-speed calcination at a high temperature of 350°C / min, and the resulting zirconia sintered body exhibits excellent light transmittance. Background Technology

[0002] Zirconia sintered bodies are widely used in industry, and in recent years they have been used in dental materials such as dental repairs. These dental repairs are typically manufactured by pressing zirconia particles or molding them using a composition containing zirconia particles to create a zirconia molded body with a desired shape, such as a disc or prism. This molded body is then pre-fired to create a pre-fired body (grind blank), which is then cut (ground) into the shape of the desired dental repair. Finally, it is further calcined.

[0003] Zirconia is a compound that undergoes phase transitions between multiple crystal systems. Therefore, partially-stabilized zirconia (PSZ) and fully-stabilized zirconia (FSZ) are used in various fields to suppress phase transitions by dissolving stabilizers such as yttrium oxide (Y₂O₃) in zirconia.

[0004] In dentistry, zirconia, while possessing high strength, has low light transmittance, thus it is primarily used for framing. Furthermore, in recent years, with the improvement in the light transmittance of zirconia, it has become increasingly common to use zirconia alone to fabricate dental restorations.

[0005] From the viewpoint that dental repairs made of zirconia materials have excellent strength and light transmittance, for example, a zirconia sintered body such as Patent Document 1 can be proposed.

[0006] Existing technical documents Patent documents Patent document 1: Japanese Patent Application Publication No. 2010-150064. Summary of the Invention

[0007] The problem the invention aims to solve Patent document 1 discloses the sintering shrinkage rate (Δρ / ΔT: g / cm³) in a region with a relative density of 70% to 90% when calcined at 5°C / min. 3 The temperature (°C) is above 0.0120 and below 0.0135, which can increase the density of the final zirconia sintered body.

[0008] However, Patent Document 1 does not mention the density change of the sintered body when heated at a rate faster than 5°C / minute.

[0009] Furthermore, as the inventors know, in the invention described in Patent Document 1, when the temperature is raised at a high speed (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 higher, and the translucency exhibited during calcination at 5°C / min is not observed. Therefore, in the invention described in Patent Document 1, it is clear that there is room for improvement in order to further shorten the calcination time.

[0010] The purpose of this invention is to provide a zirconia pre-sintered body that achieves a relative density of over 99.0% through high-speed calcination at a high temperature of 350℃ / min, and the resulting zirconia sintered body exhibits excellent light transmittance.

[0011] means for solving problems In order to solve the above-mentioned problems, the inventors conducted repeated and in-depth research and discovered that: When preparing six samples containing zirconium oxide and yttrium oxide, with six target temperatures set in 50°C increments from 1150°C to 1400°C, and heating from a temperature range below 400°C to each of the six different target temperatures at a heating rate of 350°C / min, holding each target temperature for 10 minutes, and then cooling to 25°C, the temperature range of 1150°C to 1400°C is divided into 50°C intervals. At this time, temperature ranges are set in 50°C intervals from 1150°C. The temperature range from 1150°C to 1200°C is called the first interval, the temperature range from 1200°C to 1250°C is called the second interval, and so on, setting the temperature range of the nth interval (n represents an integer greater than or equal to 1). Then, using the aforementioned six samples, the change in density of the pre-fired body at the upper limit temperature and the lower limit temperature of the pre-fired body in the nth interval (n represents an integer greater than or equal to 1) is defined as Δρ. n When the temperature change is defined as ΔT, the proportion of density change in the nth interval is Δρ in the temperature range above 1200℃ and below 1350℃. n / ΔT is the ratio of the density change in the (n+1)th interval to Δρ n+1 The change in / ΔT ((Δρ) n+1 / ΔT)-(Δρ n The zirconia pre-sintered body with a displacement point where the maximum value of / ΔT) is 0.010 or higher was found to have excellent light transmittance even when the zirconia sintered body is calcined at a high temperature of 350°C / min. Based on this insight, further research was conducted, and the present invention was completed.

[0012] This invention includes the following inventions.

[0013] [1] Zirconia pre-sintered body, comprising zirconium oxide and yttrium oxide, Six target temperatures are set in increments of 50°C, ranging from 1150°C to 1400°C. When preparing six different samples, the temperature was increased from below 400°C to six different target temperatures at a rate of 350°C / minute, held at each target temperature for 10 minutes, and then cooled to 25°C. The target temperature range of 1150℃ to 1400℃ was divided into 50℃ intervals. Using the aforementioned six types of samples, the change in density of the pre-burned body at the upper limit temperature and the density of the pre-burned body at the lower limit temperature in the nth interval (n represents an integer greater than or equal to 1) was defined as Δρ. n When the temperature change is defined as ΔT, the proportion of density change in the nth interval is Δρ in the temperature range above 1200℃ and below 1350℃. n / ΔT is the ratio of the density change in the (n+1)th interval to Δρ n+1 The change in / ΔT ((Δρ) n+1 / ΔT)-(Δρ n The maximum value of / ΔT)) is the displacement point above 0.010.

[0014] [2] According to the zirconia pre-burnt body described in [1], the content of yttrium oxide is more than 3.5 mol% and less than 7.5 mol% relative to the total molar content of zirconia and yttrium oxide.

[0015] [3] According to [1] or [2], the density at the aforementioned displacement point temperature (°C) is 4.5 g / cm³. 3 the following.

[0016] Invention Effects According to the present invention, a zirconia pre-sintered body can be provided that achieves a relative density of 99.0% or more in a high-speed calcination process based on a high-speed heating of 350°C / min, and the resulting zirconia sintered body has excellent light transmittance.

[0017] Furthermore, according to the present invention, a zirconia pre-sintered body can be provided that exhibits excellent light transmittance even when the holding time at the highest sintering temperature is 2 minutes. Detailed Implementation

[0018] [Zirconium oxide pre-fired body] The zirconia pre-fired body of the present invention comprises zirconia and yttrium oxide. Six target temperatures are set in increments of 50°C, ranging from 1150°C to 1400°C. When preparing six different samples, the temperature was increased from below 400°C to six different target temperatures at a rate of 350°C / minute, held at each target temperature for 10 minutes, and then cooled to 25°C. The target temperature range of 1150℃ to 1400℃ was divided into 50℃ intervals. Using the aforementioned six types of samples, the change in density of the pre-burned body at the upper limit temperature and the density of the pre-burned body at the lower limit temperature in the nth interval (n represents an integer greater than or equal to 1) was defined as Δρ. n When the temperature change is defined as ΔT, the proportion of density change in the nth interval is Δρ in the temperature range above 1200℃ and below 1350℃. n / ΔT is the ratio of the density change in the (n+1)th interval to Δρ n+1 The change in / ΔT ((Δρ) n+1 / ΔT)-(Δρ n The maximum value of / ΔT)) is the displacement point above 0.010.

[0019] In this specification, "zirconia composition" refers to a composition containing zirconia powder and stabilizer powder.

[0020] In this specification, "molded body" refers to an object that has not reached the semi-sintered state (pre-sintered state) or the sintered state. That is, the molded body is distinguished from the pre-sintered body and the sintered body in that it has not been calcined after being formed by molding.

[0021] In this specification, "zirconia pre-sintered body" refers to a semi-sintered object in which zirconia particles are necked (fixed) together and are not fully sintered.

[0022] In this specification, "zirconia sintered body" refers to an object in a sintered state where zirconia particles are completely sintered. In a zirconia sintered body, the zirconia particles are bonded together by sintering, and as sintering progresses, the relative density increases, resulting in densification. Therefore, it exhibits a fully sintered state with a relative density of over 95%.

[0023] In this specification, "zirconia" refers to zirconia (IV) (ZrO2), where ZrO2 particles contain trace amounts (more than 0.5% by mass and less than 3% by mass) of HfO2 relative to the amount of ZrO2. HfO2 is difficult to separate; therefore, terms such as "zirconia," "zirconia particles," and "zirconia powder" refer to substances containing both ZrO2 and HfO2. Furthermore, stabilizers dissolved in zirconia particles and / or powders are also included in "zirconia particles" and "zirconia powder," respectively.

[0024] In this instruction manual, "atmospheric pressure" refers to standard atmospheric pressure (1 atm).

[0025] In this specification, "theoretical density" is the density calculated from the sum of the volume per unit lattice and the mass contained within that lattice. For example, the theoretical density of 3 mol% yttrium-stabilized zirconium oxide is 6.095 g / cm³. 3 The theoretical density of 5.5 mol% yttrium oxide-stabilized zirconium oxide is 6.052 g / cm³. 3 .

[0026] Furthermore, in this specification, "displacement point" refers to a point in every 50°C interval within a specified temperature range, where the difference (amount of change) in the percentage of density change between adjacent intervals is not zero. Additionally, the temperature of the displacement point in the nth and (n+1)th intervals refers to (((Δρ)) n+1 / ΔT)-(Δρ n / ΔT)) is the upper limit temperature of the nth interval where the value is not 0.

[0027] It should be noted that the upper and lower limits of the numerical ranges (temperature range, content of each component, presence rate of crystal system, values ​​calculated from components, and various physical properties, etc.) in this specification can be appropriately combined.

[0028] The proportion Δρ of density change in the nth interval of the aforementioned temperature range above 1200℃ and below 1350℃ n The ratio of the density change Δρ in / ΔT and the (n+1)th interval n+1 The change in / ΔT ((Δρ) n+1 / ΔT)-(Δρ n From the viewpoint that a zirconia sintered body with a relative density of 99.0% or more and superior light transmittance can be obtained in a high-speed calcination with a high temperature rise of 350°C / min, the temperature is preferably 0.010 or more, more preferably 0.011 or more, more preferably 0.012 or more, and even more preferably 0.012 or more.

[0029] In addition, the aforementioned change ((Δρ) n+1 / ΔT)-(Δρ n From the viewpoint that zirconia sintered bodies with better light transmittance can be obtained in high-speed calcination based on high-speed heating at 350°C / min, / ΔT)) is preferably 0.050 or less, more preferably 0.045 or less, and even more preferably 0.040 or less.

[0030] The methods for determining the density of the pre-fired body and calculating the density change are as described in the examples below.

[0031] Through the aforementioned change in the zirconia pre-sintered body of the present invention (Δρ) n+1 / ΔT)-(Δρ nWithin the specified range, the reason why zirconia sintered bodies with a relative density of over 99.0% and excellent light transmittance can be obtained in high-speed calcination based on a high temperature rise of 350℃ / min is still undetermined, but it can be speculated as follows.

[0032] In high-speed calcination (hereinafter also referred to as "high-speed calcination"), which involves a high temperature rise of 350°C / min, it is assumed that the sintered body with low relative density has pores inside.

[0033] The inventors believe that: in the high-speed calcination, in the temperature range of 1200°C or higher and 1350°C or lower, the aforementioned change (Δρ) is present. n+1 / ΔT)-(Δρ n The maximum value of / ΔT)) is above 0.010, thereby suppressing rapid grain growth in the temperature region before the displacement point, thereby suppressing the incorporation of voids in the low temperature region above 1200°C and below 1350°C. In the high temperature region above 1350°C, when the zirconium oxide raw material causes a phase transformation (e.g., a phase transformation from monoclinic to tetragonal or cubic), it has the effect of promoting the discharge of voids according to the density difference of each phase.

[0034] Therefore, it can be concluded that even with high-speed calcination, a sintered body with a relative density of over 99.0% and excellent light transmittance can be obtained.

[0035] In the zirconia pre-fired body of the present invention, from the viewpoint of further promoting the discharge of voids in the high-temperature region, the density of the pre-fired body at the temperature (°C) of the aforementioned displacement point (the displacement point where the change in value is the maximum) is preferably 4.5 g / cm³. 3 The preferred value is 4.2 g / cm³. 3 The following is a further preferred value: 4.1 g / cm³ 3 the following.

[0036] Furthermore, from the viewpoint of achieving a relative density of 99.0% or higher during high-speed calcination, the density of the pre-calcined body at the displacement point temperature (°C) is preferably 3.0 g / cm³. 3 The above, more preferably 3.1 g / cm³ 3 The above is further preferred to be 3.2 g / cm³. 3 above.

[0037] The zirconia pre-burnt body contains yttrium oxide (Y2O3) as a stabilizer that can suppress the phase transformation of zirconia.

[0038] The yttrium oxide content in the zirconia pre-sintered body is preferably 2.5 mol% or more, more preferably 3.0 mol% or more, further preferably 3.5 mol% or more, and particularly preferably 4.0 mol% or more, relative to the total molar content of zirconia (zirconia (IV); ZrO2) and stabilizer. From the viewpoint that 2.5 mol% or more increases the cubic crystal system within the sintered body and improves light transmittance, this is preferable.

[0039] Furthermore, the content of the aforementioned 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. From the viewpoint of preventing strength reduction, a content of 10 mol% or less is preferred.

[0040] In the zirconia pre-calcined body of the present invention, the stabilizer capable of inhibiting the zirconia phase transformation may be only yttrium oxide, or may also include stabilizers other than yttrium oxide capable of inhibiting the zirconia phase transformation.

[0041] Other stabilizers (hereinafter referred to as "stabilizers") that can suppress the zirconium oxide phase transformation, besides yttrium oxide, include, for example, calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y₂O₃), cerium oxide (CeO₂), scandium oxide (Sc₂O₃), niobium oxide (Nb₂O₅), lanthanum oxide (La₂O₃), erbium oxide (Er₂O₃), and praseodymium oxide (Pr₂O₃, Pr₆O₃). 11 Oxides such as samarium oxide (Sm₂O₃), europium oxide (Eu₂O₃), thulium oxide (Tm₂O₃), gallium oxide (Ga₂O₃), indium oxide (In₂O₃), and ytterbium oxide (Yb₂O₃) are used. The aforementioned stabilizers can be used alone or in combination of two or more.

[0042] The zirconia pre-fired body of the present invention can contain additives other than zirconia and stabilizers, as long as the effects of the present invention are achieved. Examples of such additives include colorants (including pigments, composite pigments and fluorescent agents), alumina (Al2O3), titanium dioxide (TiO2), and silicon dioxide (SiO2).

[0043] As the aforementioned pigment, examples include oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically NiO, Cr2O3, etc.) (excluding Y2O3 and CeO2), preferably oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb, and more preferably oxides of at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb.

[0044] In addition, the zirconia pre-calcined body of the present invention may be free of erbium oxide (Er2O3).

[0045] Examples of composite pigments mentioned above include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O 4· ZrSiO4, (Co,Zn)Al2O4, etc. Examples of fluorescent agents include Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, and BaMgAl. 10 O 17 Eu et al.

[0046] The zirconia pre-sintered body of the present invention may contain a fluorescent agent. By containing a fluorescent agent in the zirconia pre-sintered body, the zirconia sintered body acquires fluorescence. The type of fluorescent agent is not particularly limited, and one or more substances capable of emitting fluorescence using light of any wavelength may be used.

[0047] Examples of fluorescent agents include substances containing metallic elements. Examples of such metallic elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one or more of these metallic elements. Among these metallic elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred.

[0048] Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the aforementioned metal elements. Other fluorescent agents include Y₂SiO₅:Ce, Y₂SiO₅:Tb, (Y,Gd,Eu)BO₃, Y₂O₃:Eu, YAG:Ce, ZnGa₂O₄:Zn, and BaMgAl. 10 O 17 Eu et al.

[0049] The content of fluorescent agent in the zirconia pre-sintered body is not particularly limited, and can be appropriately adjusted according to the type of fluorescent agent or the purpose of the zirconia sintered body. From the viewpoint that it can be preferably used as a dental patch, the content 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, relative to 100% by mass of zirconia contained in the zirconia pre-sintered body and calculated according to the oxide of the metal element contained in the fluorescent agent.

[0050] Furthermore, the content of the fluorescent agent is calculated based on the oxide of the metal element contained in the fluorescent agent. There are no limitations as long as suitable fluorescence is exhibited; it can be set to 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less. By setting this content to the lower limit or above, the fluorescence is comparable to that of natural human teeth. Furthermore, by setting this content to the upper limit or below, the reduction in light transmittance and mechanical strength can be suppressed.

[0051] Furthermore, to ensure sufficient strength for machining in the pre-sintered state, the flexural strength of the zirconia pre-sintered body of the present invention is preferably 15 MPa or more. Additionally, to facilitate machining in the pre-sintered state, the flexural strength of the zirconia pre-sintered body is preferably 70 MPa or less, more preferably 60 MPa or less.

[0052] The aforementioned bending strength was determined according to ISO 6872:2015 (Dentistry - Ceramic materials), with only the dimensions of the test piece changed; a test piece measuring 5mm × 10mm × 50mm was used. The front and C-side of the test piece (the side formed by chamfering the corners of the test piece at a 45° angle) were finished along the length using 600-grit sandpaper. The test piece was positioned with its widest face facing the vertical direction (load direction). In the three-point bending test, the distance between the support points (span) was set to 30mm, and the crosshead speed was set to 0.5mm / minute.

[0053] Furthermore, the density of the zirconia pre-fired body of the present invention is preferably 2.7 g / cm³. 3 The above, more preferably 3.0 g / cm 3 The above is further preferred to be 3.2 g / cm³. 3 above.

[0054] In addition, the density of the zirconia pre-sintered body is preferably 4.0 g / cm³. 3 The preferred value is 3.8 g / cm³. 3 The following is a further preferred value: 3.6 g / cm³ 3 The following applies. When the density is within the aforementioned range, molding can be easily performed.

[0055] The density of the zirconia pre-sintered body can be calculated using the formula (mass of the zirconia pre-sintered body) / (volume of the zirconia pre-sintered body). For example, to determine the density of the zirconia pre-sintered body, one can change the cutting position of the zirconia pre-sintered body while cutting out 10mm square test pieces (n=3) at arbitrary locations. The mass and volume of the obtained test pieces are measured, and the arithmetic mean of the measured values ​​is calculated. Using this arithmetic mean, the density is calculated according to the formula above.

[0056] [Manufacturing method of zirconia pre-sintered body] Next, the manufacturing method of the zirconia pre-fired body will be explained.

[0057] There are no particular limitations on the manufacturing method of the zirconia pre-fired body, as long as it is a manufacturing method that can obtain the desired displacement point. As a manufacturing method of the zirconia pre-fired body, it is suitable to manufacture it by the following operation: pulverizing a zirconia composition, calcining (pre-firing) a molded body formed by molding the pulverized zirconia composition until the zirconia particles are not sintered together, and in the aforementioned pulverization process, applying excessive energy compared to the prior art through pulverization under specified conditions, thereby manufacturing the zirconia pre-fired body of the present invention.

[0058] The method for manufacturing the zirconia composition involves mixing zirconia powder, which is used as a raw material powder, with yttrium oxide powder. The mixing method is not particularly limited, and known methods and apparatus can be used.

[0059] Methods for preparing zirconium oxide particles constituting zirconium oxide powder and yttrium oxide particles constituting yttrium oxide powder can include, for example, crushing processes that achieve micronization by pulverizing or breaking down coarse particles; and aggregation processes that synthesize atoms or ions through nucleation and growth processes.

[0060] The zirconium oxide used to form the aforementioned zirconium oxide powder is not particularly limited; tetragonal, monoclinic, and cubic zirconium oxides may all be used.

[0061] In zirconium oxide powder, one type can be used alone, or two or more types can be used in combination.

[0062] As zirconium oxide powder, commercially available zirconium oxide particles can be used, or commercially available powder can be pulverized using a known pulverizing and mixing device (ball mill, etc.) before use.

[0063] As yttrium oxide powder, commercially available yttrium oxide particles can be used, or commercially available powder can be pulverized using a known pulverizing and mixing device (ball mill, etc.) before use.

[0064] Commercially available zirconium oxide powders include, for example, those marketed under the trade names "Zpex (registered trademark)" (Y₂O₃ content: 3 mol%), "Zpex (registered trademark) 4" (Y₂O₃ content: 4 mol%), "Zpex (registered trademark) Smile (registered trademark)" (Y₂O₃ content: 5.5 mol%), "TZ-3Y" (Y₂O₃ content: 3 mol%), "TZ-3YS" (Y₂O₃ content: 3 mol%), "TZ-4YS" (Y₂O₃ content: 4 mol%), "TZ-6Y" (Y₂O₃ content: 6 mol%), "TZ-6YS" (Y₂O₃ content: 6 mol%), "TZ-8YS" (Y₂O₃ content: 8 mol%), and "TZ..." -10YS (Y2O3 content: 10 mol%), "TZ-3Y-E" (Y2O3 content: 3 mol%), "TZ-3YS-E" (Y2O3 content: 3 mol%), "TZ-3YB-E" (Y2O3 content: 3 mol%), "TZ-3YSB-E" (Y2O3 content: 3 mol%), "TZ-3YB" (Y2O3 content: 3 mol%), "TZ-3YSB" (Y2O3 content: 3 mol%), "TZ-3Y20AB" (Y2O3 content: 3 mol%), "TZ-8YSB" (Y2O3 content: 8 mol%), "TZ-0" (Y2O3 content: 0 mol%; monoclinic zirconia); all of the above are manufactured by Tosoh Corporation, etc.

[0065] Next, the zirconium oxide composition is further pulverized. By pulverizing under specified conditions, the desired displacement point can be obtained.

[0066] It can be inferred that in this invention, when a zirconium oxide composition containing zirconium oxide and yttrium oxide is subjected to a pulverization process under specified conditions, the mixing of zirconium oxide particles and yttrium oxide particles is promoted, resulting in a uniform compositional distribution. As a result, the temperature range that causes the zirconium oxide phase transformation is limited, and the desired displacement point, which is not seen in conventional products, is obtained. Rapid particle growth is suppressed in the temperature range before the displacement point, thereby suppressing the penetration of pores in the low-temperature range of 1200°C to 1350°C. In the high-temperature range above 1350°C, when the zirconium oxide raw material causes a phase transformation (e.g., a phase transformation from monoclinic to tetragonal or cubic), the density difference between the phases can promote the expulsion of pores. Excellent light transmittance can also be exhibited even when the holding time at the highest sintering temperature is 2 minutes.

[0067] The following method is preferred for pulverizing.

[0068] (i) Use a grinding medium with a diameter of less than 1 mm and a grinding time of more than 10 minutes, or (ii) Use a grinding medium with a diameter of more than 1 mm and a grinding time of more than 40 hours.

[0069] When using a grinding medium with a diameter of less than 1 mm, the diameter of the grinding medium is preferably 0.1 to 0.5 mm, from the viewpoint that the desired displacement point can be easily obtained by using a grinding medium with a fine diameter.

[0070] Commercially available products can be used as pulverizing media with a diameter of less than 1 mm.

[0071] Examples of grinding devices that use grinding media with a diameter of less than 1 mm include bead mills.

[0072] When using a pulverizing medium with a diameter of less than 1 mm, the pulverization time is not particularly limited. From the viewpoint of easily pulverizing yttrium oxide particles to a very small size, it is preferable to have 10 minutes or more, more preferably 12 minutes or more, further preferably 15 minutes or more, and particularly preferably 20 minutes or more. In addition, the pulverization time is preferably 20 hours or less, more preferably 10 hours or less, further preferably 5 hours or less, and particularly preferably 2 hours or less.

[0073] It should be noted that when using a pulverizing device (such as a bead mill) that pulverizes while circulating the slurry, the pulverizing time refers to the residence time of the slurry in the container (pulverizing chamber).

[0074] When using a grinding medium with a diameter of 1 mm or more, from the viewpoint that the diameter of the grinding medium is 1.5 mm or more, and more preferably 2.0 mm or more, the diameter of the grinding medium is preferably 1.5 mm or more, and more preferably 2.0 mm or more, as the diameter of the grinding medium.

[0075] Commercially available products can be used as pulverizing media with a diameter of 1 mm or more.

[0076] Examples of grinding devices that use grinding media with a diameter of 1 mm or more include ball mills.

[0077] When using a pulverizing medium with a diameter of 1 mm or more, the pulverizing time (pulverization treatment time) is not particularly limited, but is preferably more than 40 hours, more preferably 55 hours or more. From the viewpoint that by applying excessive energy compared to existing technologies when pulverizing the zirconia composition, the mixing of zirconia particles and yttrium oxide particles is promoted, resulting in a uniform compositional distribution, thereby easily obtaining the desired aforementioned displacement point, it is further preferred to be 80 hours or more, particularly preferably 100 hours or more. In addition, the pulverization treatment time is preferably 1000 hours or less, more preferably 800 hours or less, more preferably 500 hours or less, and particularly preferably 300 hours or less.

[0078] Zirconia compositions can be in the form of particles, slurries, etc.

[0079] When a zirconia composition is made into a slurry, the slurry can be manufactured by mixing the mixed powder obtained by pulverization with a solvent (suitably water).

[0080] From the viewpoint of excellent mechanical strength and light transmittance of the sintered body, the average particle size of the zirconia composition after pulverization is preferably below 0.2 μm.

[0081] The average particle size of zirconia and yttrium oxide particles can be determined using a dynamic light scattering particle size distribution measurement method. For example, a dynamic light scattering particle size distribution measurement device (trade name "SZ-100V2") manufactured by Horiba Corporation can be used to subject a slurry diluted with water to approximately 0.1% by mass to ultrasonic irradiation for 30 minutes, followed by measurement based on volume while in contact with ultrasonic waves.

[0082] In addition, the zirconia composition may contain additives such as binders, dispersants, emulsifiers, defoamers, pH adjusters, lubricants, and light transmittance adjusters. One additive may be used alone, or two or more may be used in combination.

[0083] Examples of adhesives include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, acrylic adhesives, wax adhesives, polyvinyl butyral, polymethyl methacrylate, and ethyl cellulose.

[0084] To improve light transmittance, the binder content in the zirconium oxide composition of the present invention is preferably 10% by mass or less relative to 100% by mass of zirconium oxide, more preferably 7% by mass or less, and even more preferably 5% by mass or less.

[0085] Examples of plasticizers include polyethylene glycol, glycerin, propylene glycol, and dibutylphthalic acid.

[0086] Examples of dispersants include ammonium polycarboxylate (such as triammonium citrate), ammonium polyacrylate, acrylic copolymer resins, acrylate copolymers, polyacrylic acid, bentonite, carboxymethyl cellulose, anionic surfactants (such as polyoxyethylene lauryl ether phosphate and polyoxyethylene alkyl ether phosphate), nonionic surfactants, glyceryl oleate, amine salt surfactants, oligosaccharide alcohols, stearic acid, etc.

[0087] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitol derivatives.

[0088] Examples of defoaming agents include alcohols, polyethers, polyethylene glycols, silicones, and waxes.

[0089] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxide such as tetramethylammonium hydroxide).

[0090] Examples of lubricants include polyoxyethylene alkyl ethers and waxes.

[0091] Examples of light transmittance modifiers include aluminum oxide (Al2O3), titanium dioxide (TiO2), silicon dioxide (SiO2), zircon, lithium silicate, and lithium disilicate.

[0092] The BET specific surface area of ​​the particles constituting the zirconia composition, when measured according to JIS Z 8830:2013, is preferably 7.0 m². 2 / g or more, preferably 7.5m 2 / g or more, further preferably 8.0m 2 / g or more. At 7.0m 2 When the surface area is above a certain value (e.g.), the formation of white turbidity in the sintered body can be suppressed during sintering. Furthermore, the preferred BET specific surface area is 50 m² / g. 2 / g or less, preferably 45m 2 / g or less, more preferably 40m 2 / g or less. At 50m 2 When the content is below / g, it is not easily affected by uneven temperature inside the calcining furnace.

[0093] BET surface area can be measured using commercially available devices such as the fully automated surface area measuring device (trade name "Macsorb (registered trademark) HMmodel-1200", BET flow method (single-point method / multi-point method), manufactured by Mountech). For example, the aforementioned fully automated surface area measuring device can be used to perform the measurement using the BET flow method (single-point method).

[0094] Furthermore, the light transmittance of the sintered body is not easily reduced when the calcination time for sintering is shortened. The "BET specific surface area" mentioned here refers to the specific surface area measured without distinguishing between primary and secondary particles.

[0095] Next, a molded body is produced by molding the pulverized zirconium oxide composition. The molded body is obtained by applying external force to the zirconium oxide composition and molding it using a known method.

[0096] There are no particular limitations on the molding method; for example, the following methods can be used.

[0097] (a) A process of casting a slurry containing a pulverized zirconium oxide composition; (b) A process of gel casting a slurry containing a pulverized zirconium oxide composition; (c) The process of pressing the pulverized zirconium oxide composition into shape; (d) A process for molding a zirconium oxide composition comprising zirconium oxide particles, yttrium oxide particles and resin; (e) A step of polymerizing a zirconium oxide composition comprising zirconium oxide particles, yttrium oxide particles, and polymerizable monomers and / or oligomers; and (f) Processes such as stacking particles containing zirconium oxide particles and yttrium oxide particles.

[0098] (a) Powder slurry pouring When manufacturing a zirconia molded body using a method that involves casting a slurry containing a pulverized zirconia composition, the specific method of casting the slurry is not particularly limited, and methods such as drying the slurry after it has been poured into a mold can be employed.

[0099] From the perspective of facilitating the flow of slurry into the mold, preventing excessive drying time, and increasing the number of times the mold can be used, the content of the dispersion medium in the slurry is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less.

[0100] The slurry can be poured into the mold under normal pressure, but from the point of view of production efficiency, it is preferable to do so under pressure.

[0101] (b) Gel casting When manufacturing a zirconia molded body by means of a process of gel casting a slurry containing a pulverized zirconia composition, the specific method of gel casting is not particularly limited. For example, a method can be used to obtain a shaped wet body by gelling the aforementioned slurry in a mold and then drying it.

[0102] From the perspective of preventing excessive drying time and suppressing cracks during drying, 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.

[0103] Gelation can be achieved, for example, by adding a gelling agent, or by polymerizing a polymerizable monomer after its addition.

[0104] There are no restrictions on the type of gelling agent; water-soluble gelling agents can be used, with agarose and gelatin being preferred. A single gelling agent can be used, or two or more can be used in combination. The amount of gelling agent used is not particularly limited as long as it does not cause problems such as cracking during sintering. Depending on the mass of the slurry after mixing the gelling agent, it can be set to less than 10% by mass, less than 5% by mass, or less than 1% by mass.

[0105] Furthermore, there are no particular limitations on the types of polymerizable monomers. Examples include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, propylene glycol mono(meth)acrylate, glycerol mono(meth)acrylate, erythritol mono(meth)acrylate, and other (meth)acrylate monomers; N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N,N-bis(2-hydroxyethyl)(meth)acrylamide, and other (meth)acrylamide monomers. A single polymerizable monomer can be used, or two or more monomers can be used in combination.

[0106] There is no particular limit to the amount of polymerizable monomers used, as long as problems such as cracking during sintering do not occur. Depending on the quality of the slurry after mixing the polymerizable monomers, it can be set to less than 10% by mass, less than 5% by mass, or less than 1% by mass.

[0107] When gelation is achieved by polymerization of polymerizable monomers, a polymerization initiator is preferably used. The type of polymerization initiator is not particularly limited, but photopolymerization initiators are particularly preferred. As a photopolymerization initiator, it is appropriate to select from those commonly used in industry, with photopolymerization initiators used in dental applications being preferred.

[0108] Specific examples of photopolymerization initiators include (bis)acylphosphine oxides (including salts), thioxanthones (including quaternary ammonium salts), ketals, α-diketones, coumarins, anthraquinones, benzoin alkyl ethers, and α-aminoketone compounds. A single photopolymerization initiator can be used alone, or two or more can be used in combination. Among these photopolymerization initiators, at least one selected from (bis)acylphosphine oxides and α-diketones is preferred. This allows polymerization (gelation) to occur in both the ultraviolet (including near-ultraviolet) and visible light regions. In particular, polymerization (gelation) can be fully achieved even when using any light source, such as Ar lasers, He-Cd lasers, halogen lamps, xenon lamps, metal halide lamps, light-emitting diodes (LEDs), mercury lamps, and fluorescent lamps.

[0109] There are no particular limitations on the drying method used to dry the shaped wet body. Examples include natural drying, hot air drying, vacuum drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying. One or more of these methods may be used. Among these, natural drying, dielectric heating drying, induction heating drying, and constant temperature and humidity drying are preferred in order to suppress the formation of cracks during drying.

[0110] There are no particular limitations on the types of molds used in slurry casting and gel casting. For example, porous molds made of plaster, resin, ceramics, etc., and non-porous molds made of metal, resin, etc., can be used.

[0111] (c) Pressure molding In the process of press molding the pulverized zirconium oxide composition, there is no particular limitation on the specific method of press molding, and a known press molding machine can be used.

[0112] Specific methods of pressure molding include, for example, uniaxial pressure molding.

[0113] In addition, multi-stage molding can be performed. For example, after the zirconia composition is press-molded, it can be further subjected to CIP (Cold Isostatic Pressing) treatment.

[0114] The shape of the aforementioned molded body is not particularly limited and can be disc-shaped, cuboid-shaped, or in the shape of a dental product (e.g., a crown).

[0115] The molded body can be, for example, a columnar zirconia molded body in which a zirconia composition (e.g., particles) is filled into a mold and compacted by uniaxial pressure.

[0116] The higher the surface pressure during pressure 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 pre-sintered body will harden. Therefore, the surface pressure during pressure molding of zirconia molded bodies is preferably 30~200 MPa. When the surface pressure is 30 MPa or higher, the shape retention of the zirconia molded body is excellent. In addition, when the pressure is below 200 MPa, the density of the zirconia molded body will not increase excessively, making it easier to prevent hardening.

[0117] The aforementioned molded articles also include those that have been densified by high-temperature pressure treatment, such as CIP (Cold Isostatic Pressing).

[0118] Based on the same viewpoint as mentioned above, the CIP pressure is preferably 30~200MPa.

[0119] (d) Molding of a zirconia composition containing resin When a zirconia molded body is manufactured by means of a step of molding a zirconia composition comprising zirconia particles, yttrium oxide particles and resin, the specific method used to mold the zirconia composition is not particularly limited, and can be, for example, injection molding, injection molding, extrusion molding, etc.

[0120] Alternatively, molding methods such as hot-melt dissolution (FDM), inkjet printing, and powder / binder lamination (3D printing, etc.) can be used. Among these molding methods, injection molding and injection molding are preferred, and injection molding is more preferred.

[0121] There is no particular limitation on the type of resin mentioned above, but the aforementioned adhesive is preferred.

[0122] (e) Polymerization of a zirconium oxide composition comprising zirconium oxide particles, yttrium oxide particles and containing polymerizable monomers and / or oligomers Curing can be achieved by polymerizing a zirconium oxide composition containing zirconium oxide particles, yttrium oxide particles, and polymerizable monomers and / or oligomers, thereby polymerizing the polymerizable monomers and / or oligomers in the composition.

[0123] When manufacturing zirconia molded bodies using a method that includes this polymerization process, the specific method is not particularly limited. For example, a method that polymerizes the zirconia composition within a mold can be used; a photolithography method (stereolithography; SLA) using the zirconia composition can also be employed. Among these, (b) photolithography (SLA) is preferred.

[0124] According to the photoforming method, a shape corresponding to the desired shape of the final sintered zirconia body can be imparted at a specific point in time during the manufacturing of the zirconia molded body. Therefore, this photoforming method is sometimes particularly suitable for cases where the sintered zirconia body is used as a dental material such as dental repairs.

[0125] There is no particular limitation on the type of polymerizable monomer. It can be any of the following: monofunctional (meth)acrylates, monofunctional (meth)acrylamides, etc.; and multifunctional polymerizable monomers such as difunctional aromatic compounds, difunctional aliphatic compounds, and trifunctional or higher compounds. One type of polymerizable monomer can be used alone, or two or more types can be used. Among these, multifunctional polymerizable monomers are preferred, especially when using photoforming methods.

[0126] There are no particular limitations on oligomers as long as they are compounds that are bonded to two or more of the aforementioned polymerizable monomers and have polymerizable properties.

[0127] Examples of monofunctional (meth)acrylates include 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, erythritol mono(meth)acrylate, and other (meth)acrylates containing hydroxyl groups; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, etc. Alkyl methacrylates such as tert-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, lauryl methacrylate, cetyl methacrylate, and stearyl methacrylate; alicyclic methacrylates such as cyclohexyl methacrylate and isobornyl methacrylate; methacrylates containing aromatic groups such as benzyl methacrylate and phenyl methacrylate; and methacrylates with functional groups such as 2,3-dibromopropyl methacrylate, 3-methacryloyloxypropyltrimethoxysilane, and 11-methacryloyloxyundecyltrimethoxysilane.

[0128] 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.

[0129] Among these monofunctional polymerizable monomers, from the viewpoint of excellent polymerizability, (meth)acrylamide is preferred, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide are more preferred.

[0130] Examples of difunctional aromatic compounds 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, and 2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane. Propane, 2,2-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, 1,4-bis(2-(meth)acryloyloxyethyl)benzothionate, etc. (meth)acrylates. Among these, Bis-GMA and 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles. Among 2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (average molar number of ethoxy addition: 2.6, commonly referred to as "D-2.6E") is preferred.

[0131] Examples of difunctional 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, butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 2-ethyl-1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,2-bis(3-methacryloyloxy-2-hydroxypropoxy)ethane, and 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate (commonly known as "UDMA"), etc. Among these, from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles, triethylene glycol dimethacrylate (commonly known as "TEGDMA") and UDMA are preferred.

[0132] Examples of compounds with trifunctionality or higher include 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-(aminocarboxyl)propane-1,3-diol]tetra(meth)acrylate, and 1,7-diacetoxy-2,2,6,6-tetra(meth)acryloxymethyl-4-oxaheptane (meth)acrylates. Among these, from the viewpoint of excellent polymerizability and mechanical strength of the resulting zirconia molded articles, N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxyl)propane-1,3-diol]tetramethacrylate and 1,7-diacetoxy-2,2,6,6-tetracetoxymethyl-4-oxaheptane are preferred.

[0133] In any of the methods described above, polymerization of the composition is preferably carried out using a polymerization initiator, and the composition preferably further comprises a polymerization initiator. The type of polymerization initiator is not particularly limited, but a photopolymerization initiator is particularly preferred. As a photopolymerization initiator, it can be appropriately selected from those commonly used in industry, with photopolymerization initiators used in dental applications being preferred. Specific examples of photopolymerization initiators are the same as those described above for the purpose of gel casting.

[0134] When manufacturing zirconia molded articles using a photoforming method with a zirconia composition, the specific method of photoforming is not particularly limited, and known methods can be appropriately used. For example, methods such as using a photoforming device to photopolymerize a liquid composition using ultraviolet light, laser, etc., thereby sequentially forming layers with the desired shape, and thus obtaining the zirconia molded article as the target.

[0135] To further increase the density of the zirconia molded body as a cured product, CIP treatment can be carried out after humidifying the zirconia molded body.

[0136] In the case of pressure molding, the powder containing zirconia particles can be humidified before pressure molding. The humidification method can be any known method without limitation; it can involve spraying water using a sprayer, or using a humidifier or a constant temperature and humidity device. The increase in moisture due to humidification depends on the average particle size of the contained zirconia particles, the average particle size of the stabilizer particles, etc., and is preferably more than 2% by mass, more preferably more than 3% by mass, further preferably more than 4% by mass, particularly preferably more than 5% by mass, and preferably 15% by mass or less, more preferably 13% by mass or less, and further preferably 11% by mass or less, relative to the mass of the powder before humidification and the molded body. It should be noted that the increase in moisture due to humidification can be calculated as a percentage by dividing the mass of the powder before humidification by the mass of the powder before humidification and the molded body (the mass of the powder after humidification and the molded body).

[0137] The pressure applied during CIP processing is the same as described above for the instructions on pressure molding.

[0138] (f) The process of stacking particles containing zirconium oxide particles and yttrium oxide particles. There are no particular limitations on the specific methods used to manufacture granules containing zirconium oxide and yttrium oxide particles. For example, a method can be used to produce granules by drying them in a spray dryer after slurry preparation, and the resulting granules can be used for powder lamination shaping.

[0139] There are no particular limitations on the powder lamination method, and examples include powder layering, SLS (Selective Laser Sintering), SLM (Selective Laser Melting), electron beam lamination, arc discharge lamination, and binder spraying. Regarding a better method that does not contain organic matter during lamination, it is preferable that organic matter is also not used in the particle manufacturing stage.

[0140] Next, the zirconia pre-fired body of the present invention is obtained by pre-firing the molded body.

[0141] From the viewpoint that the specific zirconium oxide composition described above can reliably achieve a semi-sintered state, the pre-firing temperature (maximum pre-firing temperature) in the pre-firing process 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.

[0142] Furthermore, from the viewpoint of ensuring processability, the preheating temperature is preferably below 1200°C, more preferably below 1150°C, even more preferably below 1100°C, and particularly preferably below 1050°C.

[0143] That is, the preferred temperature for manufacturing the zirconia pre-fired body of the present invention is 800~1200°C.

[0144] Regarding the holding time (dwelling time) at the aforementioned highest pre-firing temperature, it is possible to produce a semi-sintered state, preferably by holding at the highest pre-firing temperature for 30 minutes to 6 hours.

[0145] In addition, the heating rate up to the maximum preheating temperature and the cooling rate from the maximum preheating temperature are preferably 300°C / min or less.

[0146] In a suitable embodiment, the heating rate for raising the zirconia molded body of the present invention to the highest pre-firing temperature during pre-firing is not particularly limited, but is preferably 0.1°C / min or more, more preferably 0.2°C / min or more, even more preferably 0.5°C / min or more, and preferably 50°C / min or less, more preferably 30°C / min or less, even more preferably 20°C / min or less.

[0147] By setting the heating rate above or below the aforementioned lower limit, productivity is increased. Furthermore, by setting the heating rate below or below the aforementioned upper limit, the volume difference between the interior and exterior of the zirconia molded body and / or the zirconia pre-sintered body can be suppressed. Additionally, in the case where the zirconia molded body contains organic matter, the rapid decomposition of that organic matter can be suppressed, thereby preventing cracking and / or damage.

[0148] [Zirconium oxide sintered body] Next, the sintered zirconia body will be described.

[0149] Zirconia sintered bodies are obtained by calcining the zirconia pre-sintered body obtained by the above-described operation.

[0150] The content of stabilizers (yttrium oxide and stabilizers other than yttrium oxide) in the zirconia sintered body of the present invention is the same as the content of stabilizers in the zirconia pre-sintered body.

[0151] The zirconia sintered body of the present invention may contain a fluorescent agent. The fluorescent agent is the same as that in the zirconia pre-sintered body.

[0152] In this specification, regarding fluorescent agents, "100% by mass of zirconium oxide contained in the pre-sintered zirconium oxide body" can be understood as "100% by mass of zirconium oxide contained in the sintered zirconium oxide body".

[0153] The zirconia sintered body of the present invention may contain a colorant. Examples of colorants include those used in the zirconia pre-sintered body.

[0154] The content of colorant in the zirconia sintered body is not particularly limited and can be appropriately adjusted according to the type of colorant and the intended use of the zirconia sintered body. From the viewpoint of preferably using it as a dental patch, the content 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, based on the conversion of oxides of metal elements contained in the colorant, relative to 100% by mass of zirconia contained in the zirconia sintered body. In addition, the content of colorant, based on the conversion of oxides of metal elements 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, can be 0.1% by mass or less, and further can be 0.05% by mass or less.

[0155] To adjust the light transmittance of the zirconia sintered body of the present invention, the zirconia sintered body of the present invention may contain a light transmittance modifier. Examples of light transmittance modifiers include substances identical to those used in the zirconia pre-sintered body.

[0156] The content of the light transmittance modifier in the zirconia sintered body is not particularly limited, and can be appropriately adjusted according to the type of light transmittance modifier and the intended use of the zirconia sintered body. From the viewpoint that it can be preferably used as a dental patch, the content is preferably 0.1% by mass or less relative to 100% by mass of zirconia contained in the zirconia sintered body.

[0157] 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.

[0158] Relative density can be calculated as the ratio of the measured density, obtained by Archimedes' method, to the theoretical density.

[0159] The higher the density of the zirconia sintered body, the fewer the internal voids, and the less light scattering it is. Therefore, from the viewpoint of improving light transmittance, a density of 5.80 g / cm³ is preferred. 3 The above, more preferably 5.82 g / cm³ 3 The above is further optimized to 5.87 g / cm³. 3 The above. Zirconia sintered bodies are particularly preferred as being substantially free of voids.

[0160] The content of zirconium oxide and stabilizer in the zirconia sintered body is the same as that in the composition before sintering and / or the pre-sintered body.

[0161] Higher strength of the zirconia sintered body is preferred. For example, the biaxial bending strength is preferably 800 MPa or higher, more preferably 820 MPa or higher, and even more preferably 840 MPa or higher. The biaxial bending strength can be measured according to ISO 6872:2015.

[0162] [Method for manufacturing zirconia sintered bodies] As a method for manufacturing the zirconia sintered body of the present invention, a method for manufacturing the zirconia sintered body by calcining the aforementioned zirconia pre-sintered body can be listed.

[0163] The preferred manufacturing method includes a step of calcining the aforementioned zirconia pre-sintered body at atmospheric pressure, at a temperature of 1350°C or higher and 1700°C or lower. This manufacturing method allows for the easy production of the zirconia sintered body of the present invention, which achieves a relative density of 99.0% or higher during high-speed calcination and also exhibits excellent light transmittance.

[0164] Furthermore, the manufacturing method of the present invention enables the easy manufacture of zirconia sintered bodies with excellent light transmittance obtained after short-time sintering at the highest sintering temperature with a holding time of less than 10 minutes (e.g., 2 minutes).

[0165] When the zirconia pre-sintered body of the present invention is calcined to produce a sintered body, the highest sintering temperature is preferably the condition that the light transmittance of the zirconia sintered body reaches its maximum.

[0166] From the viewpoint that the desired zirconia sintered body can be easily obtained under normal pressure, the maximum sintering temperature is preferably above 1200°C, more preferably above 1250°C, and even more preferably above 1300°C. Furthermore, the maximum sintering temperature is preferably below 1700°C, more preferably below 1650°C, and even more preferably below 1600°C.

[0167] By setting the maximum sintering temperature above the aforementioned lower limit and below the aforementioned upper limit, sintering can be performed sufficiently, and a dense sintered body can be easily obtained. Furthermore, by setting the maximum sintering temperature below the aforementioned upper limit, the deactivation of the fluorescent agent can be suppressed.

[0168] In the case of manufacturing sintered bodies, if the holding time at the highest sintering temperature is not particularly limited, from the perspective of being able to obtain the zirconia sintered body or the like with good productivity efficiently and stably, the holding time at the highest sintering temperature is preferably 10 minutes or less, more preferably 5 minutes or less, further preferably 3 minutes or less, and particularly preferably 2 minutes or less.

[0169] The holding time is preferably 30 seconds or more, more preferably 45 seconds or more, and even more preferably 1 minute or more.

[0170] The cooling rate during the calcination process is preferably set in a way that minimizes the time required for the calcination process. For example, the heating rate can be set according to the performance of the calcination furnace to reach the highest sintering temperature in the shortest possible time. The cooling rate from the highest sintering temperature is preferably set at a rate that prevents defects such as cracks from forming in the sintered body. For example, the sintered body can be allowed to cool naturally at room temperature after heating is complete.

[0171] The pre-calcination and calcination in this invention can be carried out using a calcination furnace. There is no particular limitation on the type of calcination furnace; for example, electric furnaces and degreasing furnaces commonly used in industry can be used.

[0172] Commercially available dental calcining furnaces (such as the trade name "Sintra CS" (manufactured by Shenpaz)) can be used.

[0173] The zirconia sintered body of the present invention can be manufactured even without HIP treatment. As an optional step, HIP treatment can be performed after sintering at atmospheric pressure to further improve light transmittance and mechanical strength.

[0174] Hereinafter, the sintered body obtained by sintering at the aforementioned highest 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".

[0175] HIP processing can be performed using a known hot isostatic pressing (HIP) apparatus.

[0176] When performing HIP treatment on a single-stage sintered body, the HIP pressure is not particularly limited. However, to obtain a dense sintered body with high strength, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more. Furthermore, the upper limit of the HIP pressure is not particularly limited; for example, it can be set to 400 MPa or less, 300 MPa or less, or even 200 MPa or less.

[0177] When performing HIP treatment on the aforementioned primary sintered body, the heating 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. Furthermore, the heating 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 heating rate to the above lower limit or above, productivity will be improved.

[0178] When performing HIP treatment on the aforementioned sintered body, the HIP time (the time to maintain the highest pressure and temperature) is not particularly limited. However, to obtain a dense zirconia sintered body with high strength, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. In addition, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0179] In the method for manufacturing zirconia sintered bodies of the present invention, when performing HIP treatment on the aforementioned primary sintered body, the pressure medium is not particularly limited. From the viewpoint of minimizing the impact on zirconia, the pressure medium can be selected from at least one of oxygen, oxygen containing 3% hydrogen, air, and inactive gases (such as nitrogen, argon, etc.).

[0180] When performing HIP treatment on the aforementioned primary sintered body under an oxygen-mixed gas atmosphere, the oxygen concentration is not particularly limited; for example, it can be set to be more than 0% and less than 20%.

[0181] When using an oxygen-mixed gas, at least one of the following inert gases (such as nitrogen, argon, etc.) can be selected as the gas other than oxygen.

[0182] During the aforementioned HIP treatment, if an inert gas or the like is used in a reducing atmosphere, blackening may sometimes occur due to oxygen deficiency. In this case, to remove the blackening, it is preferable to include a heat treatment process (hereinafter also referred to as "tempering") at 1650°C or below in the atmosphere or in an oxygen-excess atmosphere after the aforementioned HIP treatment. From the viewpoint of effectively performing the heat treatment, it is more preferable to perform the heat treatment in an oxygen-excess atmosphere.

[0183] An atmosphere with excess oxygen refers to an atmosphere where the oxygen concentration is higher than that in the atmosphere.

[0184] As an oxygen-excess atmosphere, there is no particular limitation as long as the oxygen concentration exceeds 21% and is less than 100%, and it can be appropriately selected from this range. For example, the oxygen concentration can be set to 100%. During the aforementioned HIP treatment, if an inert gas or the like is used in a reducing atmosphere, blackening may sometimes occur due to oxygen deficiency. In this case, to remove the blackening, it is preferable to include a heat treatment process (hereinafter also referred to as "tempering") at 1650°C or below in the atmosphere or an oxygen-excess atmosphere after the aforementioned HIP treatment step. From the viewpoint of effectively performing the heat treatment, it is more preferable to perform it in an oxygen-excess atmosphere. An oxygen-excess atmosphere refers to an oxygen concentration higher than that in the atmosphere. As an oxygen-excess atmosphere, there is no particular limitation as long as the oxygen concentration exceeds 21% and is less than 100%, and it can be appropriately selected from this range. For example, the oxygen concentration can be set to 100%.

[0185] The zirconia sintered body of the present invention is not particularly limited as long as it achieves the effects of the present invention. It can be a single sintered body, a HIP-treated sintered body, or a sintered body after tempering treatment.

[0186] Depending on the aesthetic appeal of the zirconia sintered body (e.g., the color of dental repairs), the heat treatment temperature in the atmosphere or in an oxygen-rich atmosphere can be appropriately changed.

[0187] In a suitable embodiment, from the viewpoint of the aesthetics of the zirconia sintered body, the heat treatment temperature in the atmosphere or in an oxygen-excess atmosphere is preferably below 1650°C, more preferably below 1600°C, and even more preferably below 1550°C.

[0188] In another suitable embodiment, from the viewpoint of the aesthetics of the zirconia sintered body, the heat treatment temperature in the atmosphere or in an oxygen-excess atmosphere is preferably below 1400°C, more preferably below 1300°C, and even more preferably below 1200°C.

[0189] Furthermore, in any embodiment, the heat treatment temperature is preferably 500°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher.

[0190] The aforementioned tempering process can be performed using a standard dental zirconia calcination furnace. Commercially available zirconia calcination furnaces can be used. Examples of commercially available furnaces include Noritake KATANA (registered trademark) F-1, F-1N, and F-2 (all from SK Medical Electronics Co., Ltd.).

[0191] The zirconia sintered body obtained by calcining the zirconia pre-burnt body of the present invention is suitable for use in dental products.

[0192] Examples of dental products include, for example, inner crowns, frameworks, dental crowns, dental bridges, bridge abutments, implants, implant screws, implant fixation devices, implant bridges, implant bars, dental crowns, dentures, inlays, onlays, orthodontic wires, and veneers.

[0193] By using the zirconia pre-fired body of the present invention in components such as implant screws and implant fixation devices, it is possible to suppress gingival discoloration and achieve excellent aesthetics when using metal materials.

[0194] Furthermore, as for their manufacturing methods, appropriate methods can be selected according to various applications. For example, dental articles can be obtained by machining the zirconia pre-fired body of the present invention followed by calcination. It should be noted that a CAD / CAM system is preferably used in this machining process.

[0195] There are no particular limitations on the CAD / CAM system, and any known device can be used. Examples of known devices include, for instance, CAD / CAM systems such as "KATANA (registered trademark) CAD / CAM system" and those manufactured by Kuraray Noritake Dental Co., Ltd. As long as the present invention achieves the effects of the present invention, it includes embodiments obtained by combining all or part of the above-described structures within the scope of the technical concept of the present invention. Example

[0196] Next, embodiments are listed to illustrate the present invention in more detail, but the present invention is not limited to these embodiments at all, and those skilled in the art can make various modifications within the scope of the technical concept of the present invention.

[0197] [Example 1] Commercially available zirconium oxide powder (Y2O3: 0 mol%) and commercially available yttrium oxide powder were added to water. They and zirconium oxide grinding media (diameter: 2 mm) were then added to the container of a ball mill. The grinding process was set to 96 hours, and the ball mill was used to grind the materials to obtain a slurry (average particle size: below 0.2 μm).

[0198] Next, an organic binder is added to the resulting slurry and mixed. The mixed slurry is then dried and granulated using a spray dryer to obtain powder.

[0199] The powder is fed into a cylindrical mold and pressed under uniaxial pressure of 200 MPa to obtain a molded body.

[0200] The resulting molded body was placed in an electric furnace and heated from room temperature at a rate of 10°C / min. It was then held at 500°C for 2 hours to degrease the organic components. Subsequently, the temperature was increased at a rate of 10°C / min and held at 955°C for 2 hours. Finally, it was slowly cooled at a rate of -10°C / min to obtain a zirconia pre-fired body.

[0201] [Example 2 and Comparative Examples 1-2] Except for the conditions described in Table 1, zirconia pre-fired bodies were manufactured using the same method as in Example 1. In Example 2 and Comparative Examples 1-2, the yttrium oxide raw material used was the same as that in Example 1.

[0202] In the table, the yttrium oxide content refers to the ratio (mol%) of the number of moles of yttrium oxide to the total number of moles of zirconium oxide and yttrium oxide.

[0203] In the table, "-" indicates that no pulverization process was performed.

[0204] In addition, the yttrium oxide content refers to the value in slurry, molded body, pre-fired body and sintered body.

[0205] In addition, in the table, the commercially available product in Comparative Example 1 used a product manufactured by Tosoh Corporation (trade name "Zpex").

[0206] <Methods for determining density and calculating the proportion of density change during the manufacture of zirconia sintered bodies> The zirconia pre-fired bodies of Examples 1-2 and Comparative Examples 1-2 were pulverized under the conditions described in Table 1 and shaped into a disc shape with a diameter of approximately 18 mm and a thickness of approximately 1.2 mm to obtain a shaped body. The shaped body was held at the highest pre-firing temperature of 1000°C for 2 hours and then slowly cooled at a rate of -0.4°C / min to obtain the zirconia pre-fired body.

[0207] Six target temperatures were set at 50°C intervals from 1150°C to 1400°C. The zirconia pre-sintered bodies of each embodiment and comparative example were heated from room temperature to each target temperature using a dental calcination furnace (trade name "Sintra CS" (manufactured by Shenpaz)) at theoretical density. The samples were held at each target temperature for 10 minutes, then cooled to 25°C, resulting in six samples (zirconia sintered bodies) with different target temperatures (maximum sintering temperatures). During the aforementioned cooling, the temperature was set to -200°C / minute up to 950°C, and then the furnace was opened for cooling. All samples underwent cooling treatment under the same conditions.

[0208] The mass of the zirconia sintered body was determined using an electronic balance, the thickness and diameter were measured using a micrometer, the dimensions of each sample were accurately measured, the mass was determined using a precision balance, and the arithmetic mean of n=3 was calculated by (mass of the pre-sintered body) / (volume of the pre-sintered body).

[0209] The target temperature range of 1150℃ to 1400℃ is divided into intervals of 50℃. Using the aforementioned six types of samples, the change in density of the pre-burned body at the upper limit temperature and the density of the pre-burned body at the lower limit temperature in the nth interval (n represents an integer greater than or equal to 1) is denoted as Δρ. n With the temperature change denoted as ΔT, the proportion Δρ of the density change in the nth interval is calculated in the temperature range above 1200℃ and below 1350℃. n / ΔT, and the ratio Δρ of the density change in the (n+1)th interval. n+1 / ΔT. The results are shown in Table 2.

[0210] In the table, density is expressed in g / cm³. 3 .

[0211] Evaluation of the light transmittance of zirconia sintered bodies (determination of ΔL* (WB)) For the zirconia pre-burnt bodies obtained in each embodiment and comparative example, a short-time calcination was carried out using a dental calcination furnace (trade name "Sintra CS" (manufactured by Shenpaz)) at a heating rate of 350°C / min and a holding time of 2 minutes at 1580°C.

[0212] The obtained zirconia sintered bodies were ground into flat plates with a thickness of 1.0 mm, which were used as test samples for transmittance. The transmittance of these samples was measured using an Olympus spectrophotometer (trade name "Crystaleye") in 7-band LED light source mode.

[0213] Specifically, regarding the transmittance of zirconia sintered bodies as flat samples, the lightness (LW*) measured against a white background and the lightness (LB*) measured against a black background using the same sample, measuring apparatus, measuring mode, and light source are taken as the transmittance (ΔL*(WB)) (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).

[0214] The light transmittance ΔL*(WB) of the sintered body is considered acceptable if it is 13 or higher. The results are shown in Table 1.

[0215] <Method for calculating the relative density of zirconia sintered bodies> The zirconia pre-calcined bodies of each example and comparative example were calcined for a short time using a dental calcination furnace (trade name "Sintar CS" (manufactured by Shenpaz) at a heating rate of 350°C / min and held at 1580°C for 2 minutes.

[0216] The obtained zirconia sintered bodies were ground into flat plate samples with a thickness of 1.0 mm, which were used as density test samples. The measured density was determined by Archimedes method.

[0217] Relative density is calculated as the ratio of the measured density determined by the Archimedes method to the theoretical density.

[0218] The results are shown in Table 1.

[0219] As described above, by using the zirconia pre-sintered body of the present invention, a zirconia sintered body with a relative density of 99.0% or higher and excellent light transmittance is obtained in a high-speed calcination process based on a high-speed heating rate of 350°C / min.

[0220] In the comparative example, zirconia sintered bodies that achieve the theoretical density and have excellent light transmittance cannot be obtained.

[0221] Industrial utilization The zirconia pre-fired body of the present invention is useful for manufacturing dental articles used in dental hospital treatments.

Claims

1. Zirconia pre-sintered body, comprising zirconium oxide and yttrium oxide, Six target temperatures are set in increments of 50°C, ranging from 1150°C to 1400°C. When preparing six different samples, the temperature was increased from below 400°C to six different target temperatures at a rate of 350°C / minute, held at each target temperature for 10 minutes, and then cooled to 25°C. The target temperature range of 1150℃ to 1400℃ was divided into 50℃ intervals. Using the aforementioned six types of samples, the change in density of the pre-burned body at the upper limit temperature and the density of the pre-burned body at the lower limit temperature in the nth interval (n represents an integer greater than or equal to 1) was defined as Δρ. n When the temperature change is defined as ΔT, the proportion of density change in the nth interval is Δρ in the temperature range above 1200℃ and below 1350℃. n / ΔT is the ratio of the density change in the (n+1)th interval to Δρ n+1 The change in / ΔT ((Δρ) n+1 / ΔT)-(Δρ n The maximum value of / ΔT)) is the displacement point above 0.

010.

2. The zirconia pre-fired body according to claim 1, wherein, The content of yttrium oxide relative to the total molar content of zirconium oxide and yttrium oxide is above 3.5 mol% and below 7.5 mol%.

3. The zirconia pre-fired body according to claim 1 or 2, wherein, The density at the aforementioned displacement point at the specified temperature (°C) is 4.5 g / cm³. 3 the following.

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