Zirconia composite sintered body

Abstract

This invention provides a zirconia composite sintered body with strength suitable for dental applications, excellent machinability in the sintered state, and excellent aesthetics. The invention relates to a zirconia composite sintered body comprising: zirconia, a stabilizer capable of inhibiting the zirconia phase transformation, and at least one selected from Nb₂O₅ or Ta₂O₅, wherein the zirconia composite sintered body has multiple layers with different contents of at least one of the aforementioned stabilizer, Nb₂O₅, or Ta₂O₅ relative to the total molar amounts of zirconia, the aforementioned stabilizer, Nb₂O₅, and a₂O₅.

Description

Technical Field

[0001] This invention relates to zirconia composite sintered bodies. More specifically, this invention relates to zirconia composite sintered bodies having strength suitable for dental applications, excellent machinability in the sintered state, and excellent aesthetics. Background Technology

[0002] Ceramics formed from metal oxides are widely used in industry. Among them, zirconia sintered bodies are used in dental materials such as dental restorations due to their high strength and aesthetics.

[0003] Zirconia sintered bodies possess excellent strength, thus virtually eliminating breakage issues when used in dental materials such as restorations. Furthermore, zirconia sintered bodies exhibit high translucency and are resistant to staining in the oral cavity, resulting in excellent aesthetics. On the other hand, the high hardness of fully sintered zirconia bodies makes them virtually impossible to machine using dental processing machines. For example, machining a cubic zirconia sintered body to obtain a shape that conforms to the patient's teeth is extremely time-consuming, requiring a significant amount of metalworking tools, even for a single dental restoration.

[0004] For this reason, when using zirconia sintered bodies for dental material applications, a pre-sintered body in an easily machinable semi-sintered state, rather than a fully sintered body, is typically machined into the desired shape for a dental patch, and then further sintered to create a sintered body shaped like the target dental patch. Subsequently, when the sintered body, shaped like a dental patch, is fitted into a patient's mouth at a dental clinic, minor adjustments are made to ensure a comfortable fit.

[0005] In addition, in recent years, when pre-fired bodies are machined into the desired shape for dental restorations, machining based on CAD / CAM systems is used. These CAD / CAM systems can obtain a shape that conforms to the teeth at the patient's treatment site. Pre-fired bodies (ground blanks) are commonly used with CAD / CAM systems.

[0006] As mentioned above, when using zirconia sintered bodies for dental material applications, extensive machining is avoided after the sintered body is formed due to the unique problems of zirconia during sintering. Machining of the sintered body is limited to fine-tuning before installation in a patient's mouth in a dental hospital. In other words, the dental material application is addressed by following the phased changes in physical properties caused by the sintering of zirconia.

[0007] Furthermore, in dental treatment, considering the unique circumstances caused by the physical properties of the aforementioned zirconia sintered body, the treatment typically involves the following multiple steps: obtaining information about the shape of the patient's oral cavity, such as tooth alignment information; machining the pre-burned body (blank) into the desired shape for dental restorations using a CAD / CAM system based on the obtained information; sintering the pre-burned body with the desired shape for dental restorations to obtain the sintered body; and making minor adjustments to the sintered body to ensure a proper fit and prevent discomfort when it is installed in the patient's oral cavity at a dental hospital.

[0008] In this situation, a pre-fired body that can shorten the process of firing the aforementioned pre-fired body to obtain a sintered body has also been proposed (for example, Patent Document 1).

[0009] Patent Document 1 discloses a zirconia pre-sintered body containing zirconia and a stabilizer capable of inhibiting the zirconia phase transformation. The main crystal system of the zirconia is monoclinic. The zirconia pre-sintered body has multiple layers with different stabilizer contents relative to the total molar amount of zirconia and stabilizer.

[0010] However, in dental treatments using zirconia sintered dental restorations, it is difficult to complete all the above procedures in one visit to the dentist. Therefore, even for the treatment of a single tooth, multiple visits to the dental clinic are often required, and the treatment period from start to finish can often exceed one month.

[0011] On the other hand, from the perspective of reducing the time until new artificial teeth are installed after treatment and reducing the burden of going to and from the hospital, patients expect to visit the hospital as few times as possible and want to complete treatment in a short period of time, which is increasing year by year.

[0012] Assuming that extensive machining can be performed in the zirconia sintered state, without the need for machining in the pre-sintered state followed by sintering to create the sintered body, and after obtaining information about the shape of the patient's oral cavity, the unprocessed sintered body can be machined into the desired shape of a dental restoration using a CAD / CAM system, installed in the patient's oral cavity, and fine-tuned. This process can also complete dental treatment within a day.

[0013] Furthermore, when using dental restorations, dental treatments that can be completed in one day can also be achieved using materials other than zirconia, such as lithium disilicate glass ceramics and feldspar glass ceramics. However, in the case of zirconia sintered bodies, there are unique issues caused by the physical properties of zirconia sintered bodies, making it highly difficult to achieve.

[0014] As mentioned above, there is a high demand for zirconia in terms of both strength and aesthetics. Therefore, with the increasing demand for shortening treatment time, the following zirconia sintered body has been proposed. Unlike the previous zirconia materials that were obtained by machining a pre-fired body and then firing it, the sintered body has excellent machinability and can be machined from prismatic or disc-shaped blanks into the desired shape of dental patch (e.g., Patent Documents 2-3).

[0015] Patent document 2 discloses a processable zirconia and its manufacturing method. The processable zirconia is a sintered body formed by comprising tetragonal zirconia composite powder and TiO2 nanopowder. The tetragonal zirconia composite powder comprises 79.8~92 mol% ZrO2 and 4.5~10.2 mol% Y2O3, and contains 3.5~7.5 mol% Nb2O5 or 5.5~10.0 mol% Ta2O5. The mass ratio of TiO2 nanopowder to the aforementioned zirconia composite powder is greater than 0% by mass and less than 2.5% by mass.

[0016] In addition, Patent Document 3 discloses a zirconia composite sintered body and its manufacturing method, wherein the zirconia composite sintered body contains 78-95 mol% ZrO2, 2.5-10 mol% Y2O3, and contains 2-8 mol% Nb2O5 and / or 3-10 mol% Ta2O5, and the zirconia composite sintered body uses raw material with monoclinic ZrO2 as the main crystalline phase and has machinability.

[0017] Existing technical documents Patent documents Patent Document 1: International Publication No. 2020 / 138316 Patent Document 2: Japanese Patent Application Publication No. 2015-127294 Patent document 3: International Publication No. 2021 / 132644. Summary of the Invention

[0018] The problem the invention aims to solve In Patent Document 1, by stacking zirconium oxide powders with different yttrium oxide contents, a highly transparent layer and an opaque layer can be reproduced. However, it needs to be sintered after machining, which increases the treatment time for patients. From the perspective of shortening the treatment time, there is still room for improvement.

[0019] Furthermore, the inventors have discovered that the zirconia sintered bodies disclosed in Patent Documents 2 and 3 can be machined in the sintered state, but there is no record of layering. The transparency of the cut end and the tooth neck becomes the same. In order to maintain the machinability in the sintered state and present an appearance that is closer to natural teeth even when at very close range, there is still room for further improvement.

[0020] Furthermore, when the composition is altered to improve machinability and reduce material hardness, the material strength is reduced. Therefore, it is difficult to provide a zirconia sintered body that possesses the following properties: excellent strength, excellent mechanical properties in the sintered state, and, moreover, different transparency at the cut end and at the neck of the tooth, enabling the production of dental restorations that more closely resemble natural teeth in appearance.

[0021] The purpose of this invention is to provide a zirconia composite sintered body with strength suitable for dental applications, excellent machinability in the sintered state, and excellent aesthetics.

[0022] means for solving problems In order to solve the above-mentioned problems, the inventors have repeatedly conducted in-depth research and found that the problems can be solved by preparing a zirconia composite sintered body containing zirconia, a stabilizer that can suppress the zirconia phase transformation, and at least one of Nb2O5 or Ta2O5, and having a different content of at least one of the aforementioned stabilizer, Nb2O5, or Ta2O5 relative to the total molar amount of zirconia, the aforementioned stabilizer, Nb2O5, and Ta2O5. Based on this insight, further research was conducted, and the present invention was completed.

[0023] That is, the present invention includes the following technical solutions.

[0024] [1] A zirconia composite sintered body, comprising: zirconium oxide, a stabilizer capable of inhibiting the zirconium oxide phase transformation, and at least one selected from Nb2O5 or Ta2O5. The zirconia composite sintered body comprises multiple layers having different contents of at least one of the aforementioned stabilizers, Nb2O5, or Ta2O5 relative to the total molar amounts of zirconia, the aforementioned stabilizers, Nb2O5, and Ta2O5.

[0025] [2] According to the zirconia composite sintered body described in [1], wherein the aforementioned multiple layers are multiple layers with different contents of Nb2O5 or Ta2O5.

[0026] [3] According to the zirconia composite sintered body described in [2], in a straight line extending from one end of the aforementioned zirconia composite sintered body toward the other end, from the aforementioned one end toward the other end, the tendency of the content of Nb2O5 or Ta2O5 to increase or decrease does not change relative to the total molar of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5.

[0027] [4] According to the zirconia composite sintered body described in [3], the aforementioned stabilizer is yttrium oxide.

[0028] [5] According to the zirconia composite sintered body described in [4], wherein, relative to the total molar amounts of zirconia, yttrium oxide, Nb2O5 and Ta2O5, The content of Nb₂O₅ or Ta₂O₅ in the layer containing the aforementioned end is 2 mol% or more and 12 mol% or less. The content of Nb2O5 or Ta2O5 in the layer at the other end mentioned above is more than 1 mol% and less than 10 mol%.

[0029] [6] According to the zirconia composite sintered body described in [1], wherein the aforementioned multiple layers are multiple layers with different contents of the aforementioned stabilizer.

[0030] [7] According to the zirconia composite sintered body described in [6], in a straight line extending from one end of the aforementioned zirconia composite sintered body toward the other end, from one end of the aforementioned zirconia composite sintered body toward the other end, the tendency of the content of the aforementioned stabilizer to increase or decrease relative to the total molar of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5 does not change.

[0031] [8] The zirconia composite sintered body according to [7], wherein the aforementioned stabilizer is yttrium oxide.

[0032] [9] According to the zirconia composite sintered body described in [8], wherein, relative to the total molar amounts of zirconia, yttrium oxide, Nb2O5 and Ta2O5, The yttrium oxide content, including the layer at one end mentioned above, is between 1 mol% and 8 mol%. The yttrium oxide content of the layer at the other end mentioned above is more than 2 mol% and less than 9 mol%.

[0033]

[10] The zirconia composite sintered body according to any one of [1] to [9], wherein at least one of the aforementioned plurality of layers further comprises an element or ion derived from a capping agent.

[0034]

[11] According to the zirconia composite sintered body of

[10] , wherein the content of the aforementioned elements or ions derived from the capping agent is more than 0 mol% and less than 5 mol% relative to the total of 100 mol% of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5.

[0035]

[12] The zirconia composite sintered body according to

[10] or

[11] , wherein the aforementioned element or ion derived from the capping agent is an element or ion belonging to the 2nd to 7th period of the periodic table and whose first ionization energy is smaller than that of the group 18 element of the same period, and / or an element or ion with high electron affinity.

[0036]

[13] The zirconia composite sintered body according to

[10] or

[11] , wherein the aforementioned element or ion derived from the capping agent comprises at least one element or ion selected from Cu, Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl and F.

[0037]

[14] The zirconia composite sintered body according to

[10] or

[11] , wherein the aforementioned element or ion derived from the capping agent comprises at least one element or ion selected from Li, Na, K, Rb, Cs and Fr.

[0038]

[15] The zirconia composite sintered body according to any one of [1] to

[14] , wherein the content of the aforementioned stabilizer is set to A mol%, and the total content of Nb2O5 and Ta2O5 is set to B mol%, The A / B ratio of at least one of the aforementioned layers satisfies a value of 0.9 or higher and 3 or lower.

[0039]

[16] The zirconia composite sintered body according to any one of [1] to

[15] , wherein at least one of the aforementioned plurality of layers further comprises a zirconia reinforcing agent, wherein the content of the aforementioned zirconia reinforcing agent is more than 0% by mass and less than 6.0% by mass relative to the total mass% of zirconia, the aforementioned stabilizer, and Nb2O5 and Ta2O5.

[0040]

[17] The zirconia composite sintered body according to

[16] , wherein the aforementioned zirconia reinforcing agent comprises TiO2 and / or Al2O3.

[0041]

[18] The zirconia composite sintered body according to any one of [1] to

[17] , wherein the average grain size of the aforementioned zirconia composite sintered body is 0.5 to 5.0 μm.

[0042] Invention Effects According to the present invention, a zirconia composite sintered body with strength suitable for dental applications, excellent machinability and aesthetics in the sintered state can be provided.

[0043] Furthermore, according to the present invention, not only is the light transmittance excellent, but the transparency of the cut end and the neck of the tooth in the dental patch obtained after machining is different. Due to the gradual change in light transmittance, a dental patch that looks closer to a natural tooth can be obtained. Therefore, even at a very close distance to the object (e.g., about 45 cm), the same aesthetics as natural teeth can be obtained. Detailed Implementation

[0044] The zirconia composite sintered body of the present invention comprises: zirconium oxide, a stabilizer capable of inhibiting the zirconium oxide phase transformation (hereinafter also referred to as "stabilizer"), and at least one selected from Nb2O5 or Ta2O5. The zirconia composite sintered body comprises multiple layers having different contents of at least one of the aforementioned stabilizers, Nb2O5, or Ta2O5 relative to the total molar amounts of zirconia, the aforementioned stabilizers, Nb2O5, and Ta2O5.

[0045] In this specification, "molded body" refers to an object that is not in a semi-sintered (pre-sintered) or sintered state. That is, a molded body is distinguished from a pre-sintered body and a sintered body in that it is formed by molding but has not been fired.

[0046] In this specification, "zirconia composite pre-sintered body" refers to a semi-sintered object in which zirconium oxide and other raw material powders are necked (fixed) together and have not yet been fully sintered.

[0047] In this specification, "zirconia composite sintered body" refers to an object in a sintered state where raw material powders such as zirconia are completely sintered. In the zirconia composite sintered body, the raw material powders such as zirconia are solidified or dissolved together through sintering, and the relative density increases with sintering, thus achieving densification. Therefore, it is a fully sintered state with a relative density of 95% or more.

[0048] In this specification, "zirconia" refers to zirconia (IV) (ZrO2) containing trace amounts (more than 0.5% by mass and less than 3% by mass) of HfO2 relative to ZrO2. HfO2 is difficult to separate; therefore, terms such as "zirconia" and "zirconia powder" imply the presence of both ZrO2 and HfO2. Furthermore, powders in which stabilizers are dissolved in zirconia are also included in the term "zirconia powder."

[0049] In this instruction manual, "atmosphere" refers to standard atmospheric pressure (1 atm).

[0050] In this specification, "zirconia reinforcing agent" refers to a component that has the function of improving the mechanical strength of zirconia composite sintered bodies.

[0051] In this specification, the content of each component in the zirconia composite sintered body can be calculated based on the amount of raw materials fed.

[0052] In this specification, machining includes cutting and grinding. Furthermore, machining can be either wet or dry machining, without particular limitation.

[0053] It should be noted that, in this specification, the upper and lower limits of the numerical ranges (temperature range, content of each component, presence rate of crystal system, composition, and values ​​calculated based on them and various physical properties, etc.) can be appropriately combined.

[0054] In this specification, "the content of at least one component in the stabilizer, Nb2O5 or Ta2O5 is different" means that the difference in the interlayer content of at least one component in the stabilizer, Nb2O5 or Ta2O5 is 0.05 mol% or more, preferably 0.08 mol% or more, more preferably 0.09 mol% or more, further preferably 0.10 mol% or more, and particularly preferably 0.11 mol% or more.

[0055] In addition, the difference in interlayer content of at least one of the stabilizer, Nb2O5 or Ta2O5 is preferably 3.0 mol% or less, more preferably 2.8 mol% or less, even more preferably 2.5 mol% or less, and particularly preferably 2.0 mol% or less.

[0056] The zirconia composite sintered body of the present invention comprises a layered structure containing zirconia in all layers, a stabilizer capable of inhibiting zirconia phase transformation, and at least one selected from Nb2O5 or Ta2O5. Relative to the total molar amounts of zirconium oxide, the aforementioned stabilizer, Nb₂O₅, and Ta₂O₅, The aforementioned layered structure comprises multiple layers with different contents of at least one of the aforementioned stabilizer, Nb2O5, or Ta2O5.

[0057] In this specification, "the content of a certain component is different relative to the total molarity of zirconium oxide, the aforementioned stabilizer, Nb2O5 and Ta2O5" means that when calculating the total molarity of zirconium oxide, the aforementioned stabilizer, Nb2O5 and Ta2O5 in a specific layer, and calculating the total molarity of zirconium oxide, the aforementioned stabilizer, Nb2O5 and Ta2O5 in another specific layer, the content of a certain component (at least one of the aforementioned stabilizer, Nb2O5 or Ta2O5) between the aforementioned specific layer and the specific other layer is different.

[0058] Furthermore, the reason why the zirconia composite sintered body of the present invention maintains strength while exhibiting excellent machinability in the sintered state is still uncertain. It can be speculated that this is achieved through the following operations: by adding at least one of Nb2O5 or Ta2O5 to the conventional zirconia with added stabilizers to improve fracture toughness (IF method), and by minimizing hardness through coarsening of the microstructure.

[0059] The reason why the zirconia composite sintered body of the present invention has an aesthetic appearance similar to natural teeth is as follows.

[0060] It can be considered that in a sintered body containing at least one of Nb2O5 or Ta2O5 in addition to the aforementioned stabilizer, by having multiple layers with different contents of at least one of the stabilizer, Nb2O5, or Ta2O5 relative to the total molarity of zirconium oxide, the aforementioned stabilizer, Nb2O5, and Ta2O5, the crystal grains in the layer corresponding to the cut end are larger and have high light transmittance compared to the layer corresponding to the tooth neck, and conversely, the crystal grains in the layer corresponding to the tooth neck are smaller and have decreased light transmittance compared to the cut end.

[0061] The result can be considered that the dental repairs obtained after machining have the same or higher translucency as natural teeth, and can achieve a full gradient of translucency even compared with natural teeth.

[0062] Regarding the zirconia composite sintered body of the present invention, in a laminated structure in which all layers contain zirconia, a stabilizer, and at least one selected from Nb2O5 or Ta2O5, by changing any one of (1) the content of at least one of Nb2O5 or Ta2O5 relative to the content of the stabilizer, (2) the content of the stabilizer relative to the content of Nb2O5, or (3) the content of the stabilizer relative to the content of Ta2O5, it is possible to simultaneously possess the following properties as described above: machinability in the sintered state, and the ability to provide dental repairs with excellent strength and an appearance more similar to natural teeth.

[0063] In this specification, the description relating to the zirconia composite sintered body of the present invention, unless otherwise specifically mentioned, applies to all embodiments.

[0064] In addition, the information regarding each component and its content can be applied to all layers in a laminated structure, unless otherwise specified.

[0065] In the zirconia composite sintered body of the present invention, the content of zirconia is preferably 78 to 97.5 mol% of the total 100 mol% of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5. From the viewpoint of superior light transmittance and strength, it is more preferably 79 mol% or more and 96 mol% or less, even more preferably 80 mol% or more and 94 mol% or less, and particularly preferably 81 mol% or more and 93 mol% or less.

[0066] In the zirconia composite sintered body of the present invention, stabilizers capable of suppressing the zirconia phase transformation include, for example, calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y₂O₃), cerium oxide (CeO₂), scandium oxide (Sc₂O₃), 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), when combined with other components including at least one of Nb₂O₅ or Ta₂O₅, are preferred from the viewpoint of excellent machinability and strength in the sintered state and excellent aesthetics, resulting in a patch that more closely resembles natural teeth after machining. Y₂O₃ (yttrium oxide) and / or CeO₂ are preferred. The aforementioned stabilizers can be used alone or in combination of two or more.

[0067] In the zirconia composite sintered body of the present invention, the content of the stabilizer is preferably 1 to 12 mol% in the total of 100 mol% of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5. From the viewpoint of easily obtaining sufficient machinability, it is more preferably 2 mol% or more and 10 mol% or less. From the viewpoint of superior light transmittance and strength, it is even more preferably 3 mol% or more and 8.0 mol% or less, even more preferably 3.5 mol% or more and 7.5 mol% or less, particularly preferably 3.8 mol% or more and 7.0 mol% or less, and most preferably 4.0 mol% or more and 6.5 mol% or less.

[0068] In the zirconia composite sintered body of the present invention, the content of Nb2O5 or Ta2O5 is preferably 1 to 9 mol% of the total 100 mol% of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5, more preferably 1.5 mol% or more and 8.5 mol% or less. From the viewpoint of having better machinability, it is further preferably 2.5 mol% or more and 8.0 mol% or less, even more preferably 2.7 mol% or more and 7.0 mol% or less, particularly preferably 2.8 mol% or more and 6.0 mol% or less, and most preferably 3.0 mol% or more and 5.5 mol% or less.

[0069] If the content of Nb2O5 or Ta2O5 is within the aforementioned range, it can suppress the occurrence of defects such as notches and obtain sufficient machinability.

[0070] In all layers of the zirconia composite sintered body, the contents of zirconia, stabilizer, Nb2O5 and Ta2O5 are included within the aforementioned range.

[0071] The number of layers in the stacked structure of the zirconia composite sintered body of the present invention is not particularly limited, and can be set to 2 to 10 layers, 3 to 6 layers, or 4 to 5 layers.

[0072] As a suitable implementation, a zirconia composite sintered body with 3 to 5 layers in the aforementioned stacked structure can be cited as an example.

[0073] In the layered structure of the zirconia composite sintered body of the present invention, when the aforementioned layered structure has n layers (n is preferably an integer of 3 or more and 10 or less), the light transmittance ΔL with respect to the first layer (the layer corresponding to the cut end) is... * Transmittance ΔL of (WB) and the nth layer (corresponding to the neck of the tooth) * The difference in (WB) is preferably 1.2 or more from the viewpoint of obtaining an appearance that is closer to that of natural teeth. More preferably 1.5 or more from the viewpoint of obtaining the same aesthetics as natural teeth even at a very close distance (e.g., about 45 cm) from the viewpoint of obtaining the same aesthetics as natural teeth. More preferably 1.8 or more, and particularly preferably 2.0 or more.

[0074] Additionally, regarding the light transmittance ΔL of the first layer (equivalent to the layer at the cut end) * Transmittance ΔL of (WB) and the nth layer (corresponding to the neck of the tooth) * The difference in (WB) is preferably 6.0 or less, more preferably 5.5 or less, even more preferably 5.0 or less, and particularly preferably 4.5 or less, from the viewpoint of obtaining an appearance closer to natural teeth.

[0075] Light transmittance ΔL *The method for determining (WB) is as described in the examples described below.

[0076] Hereinafter, suitable embodiments of the zirconia composite sintered body of the present invention will be described.

[0077] As a suitable embodiment (hereinafter also referred to as the "first embodiment"), the following zirconia composite sintered body can be listed, which contains zirconia, a stabilizer capable of inhibiting the zirconia phase transformation, and at least one selected from Nb2O5 or Ta2O5. The zirconia composite sintered body has multiple layers with different contents of Nb2O5 or Ta2O5 relative to the total molar amounts of zirconia, the aforementioned stabilizer, Nb2O5, and Ta2O5.

[0078] In the layered structure of the zirconia composite sintered body described in the first embodiment, as long as a dental patch with an appearance more similar to natural teeth can be obtained, the tendency of increasing or decreasing the content of Nb2O5 or Ta2O5 can change.

[0079] In the first embodiment, for example, from the viewpoint that a dental patch that can be obtained with an appearance more similar to natural teeth can be obtained through the gradual change in light transmittance, a zirconia composite sintered body can be cited, wherein the difference in the content of Nb2O5 or Ta2O5 between adjacent layers is 0.08 mol% or more and 3.0 mol% or less.

[0080] Furthermore, in the first embodiment, from the viewpoint that a dental patch with an appearance more similar to natural teeth can be obtained through the gradual change in light transmittance, the following zirconia composite sintered body is more preferred, wherein, on a straight line extending from one end of the zirconia composite sintered body to the other end, from the aforementioned one end to the other end, the tendency of the content of Nb2O5 or Ta2O5 to increase or decrease with respect to the total molarity of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5 does not change.

[0081] In this specification, the aforementioned "one end" can be defined as the cut end side, the "layer containing one end" can be defined as the layer on the cut end side, the aforementioned "other end" can be defined as the neck side, and the "layer containing the other end" can be defined as the layer on the neck side.

[0082] In the first embodiment, from the viewpoint that not only does it have excellent light transmittance, but the transparency of the cut end and the neck of the tooth in the dental patch obtained after machining is also different, it is easy to obtain a gradient of light transmittance, and it is easy to obtain a dental patch that is more similar in appearance to natural teeth, the following zirconia composite sintered body is more preferred, wherein, from one end to the other, the tendency of the content of Nb2O5 or Ta2O5 to decrease relative to the total molar of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5 does not change.

[0083] Furthermore, in the first embodiment, from the viewpoint of obtaining a dental patch with superior strength and machinability in the sintered state, and with an appearance more similar to natural teeth through the gradual change in light transmittance, relative to the total molar amounts of zirconium oxide, the aforementioned stabilizer, Nb2O5, and Ta2O5, Further preferred are the following zirconium oxide composite sintered bodies: The content of Nb₂O₅ or Ta₂O₅ in the layer containing the aforementioned end is 2 mol% or more and 12 mol% or less. The content of Nb2O5 or Ta2O5 in the layer at the other end mentioned above is more than 1 mol% and less than 10 mol%. More preferably, the following zirconium oxide composite sintered body is preferred: The content of Nb₂O₅ or Ta₂O₅ in the layer containing the aforementioned end is more than 2 mol% and less than 8 mol%. The content of Nb2O5 or Ta2O5 in the layer at the other end mentioned above is more than 1 mol% and less than 6 mol%. The following zirconia composite sintered bodies are particularly preferred: The content of Nb₂O₅ or Ta₂O₅ in the layer at one end mentioned above is 2.5 mol% or more and 6 mol% or less. The content of Nb2O5 or Ta2O5 in the layer at the other end mentioned above is 1.5 mol% or more and 5 mol% or less.

[0084] Furthermore, by defining the range of Nb2O5 or Ta2O5 content in the layer containing the aforementioned other end, it is possible to further reduce the crystalline particles in the zirconia composite sintered body, thereby reducing the light transmittance of the layer corresponding to the tooth neck, i.e., the layer containing the other end, so that it falls within the range where the resulting dental patch has an appearance more similar to natural teeth.

[0085] As another suitable embodiment (hereinafter also referred to as the "second embodiment"), the following zirconia composite sintered body can be listed, which contains zirconia, a stabilizer capable of inhibiting the zirconia phase transformation, and at least one selected from Nb2O5 or Ta2O5. The zirconia composite sintered body has multiple layers with different stabilizer contents relative to the total molar amounts of zirconia, the aforementioned stabilizer, Nb2O5, and Ta2O5.

[0086] In the layered structure of the zirconia composite sintered body described in the second embodiment, as long as a dental patch with an appearance more similar to natural teeth can be obtained, the tendency to increase or decrease the content of stabilizer can change.

[0087] In the second embodiment, for example from the viewpoint that a dental patch that more closely resembles the appearance of natural teeth can be obtained through the gradual change in light transmittance, the following zirconia composite sintered body can be listed, wherein the difference in the content of stabilizer between adjacent layers is 0.08 mol% or more and 3.0 mol% or less.

[0088] Furthermore, in the second embodiment, from the viewpoint that a dental patch with an appearance more similar to natural teeth can be obtained through the gradual change in light transmittance, the following zirconia composite sintered body is more preferred, wherein, on a straight line extending from one end of the zirconia composite sintered body to the other end, from one end of the aforementioned zirconia composite sintered body to the other end, the tendency of the content of the aforementioned stabilizer to increase or decrease relative to the total molar of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5 does not change.

[0089] In the second embodiment, from the viewpoint that not only does it have excellent light transmittance, but the cut end and the neck of the tooth in the dental patch obtained after machining have different transparency, it is easy to obtain a gradual change in light transmittance, and it is easy to obtain a dental patch that is more similar in appearance to natural teeth, the following zirconia composite sintered body is more preferred, wherein, from one end to the other, the content of the aforementioned stabilizer does not change with respect to the total molar of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5.

[0090] Furthermore, in the second embodiment, from the viewpoint of having superior strength and machinability in the sintered state, and being able to obtain dental restorations with an appearance more similar to natural teeth through the gradual change in light transmittance, relative to the total molar amounts of zirconium oxide, the aforementioned stabilizer, Nb2O5, and Ta2O5, Further preferred are the following zirconium oxide composite sintered bodies: The content of the stabilizer (suitably yttrium oxide) in the layer comprising the aforementioned end is 1 mol% or more and 8 mol% or less. The content of the stabilizer (suitably yttrium oxide) in the layer at the other end is 2 mol% or more and 9 mol% or less; More preferably, the following zirconium oxide composite sintered body is preferred: The content of the stabilizer (suitably yttrium oxide) in the layer at the aforementioned end is 2 mol% or more and 8 mol% or less. The content of the stabilizer (suitably yttrium oxide) in the layer at the other end is 3 mol% or more and 9 mol% or less; The following zirconia composite sintered bodies are particularly preferred: The stabilizer (suitably yttrium oxide) contained in the layer at one end has a content of 3 mol% or more and 7.5 mol% or less. The stabilizer (suitably yttrium oxide) contained in the layer at the other end has a content of 4 mol% or more and 8.5 mol% or less.

[0091] Furthermore, when the stabilizer for the layer at the other end is yttrium oxide, within the aforementioned range of yttrium oxide content, if it is a conventional zirconia sintered body stabilized with yttrium oxide, increasing the yttrium oxide content will increase the light transmittance. However, in a zirconia composite sintered body containing at least one of Nb2O5 or Ta2O5, the crystalline particles in the zirconia composite sintered body can be further reduced. This can lower the light transmittance of the layer corresponding to the tooth neck, i.e., the layer containing the other end, so that it falls within the range where the resulting dental patch has an appearance more similar to natural teeth.

[0092] Furthermore, in any embodiment of the present invention, from the viewpoint that the zirconia composite sintered body has better machinability in the sintered state, at least one layer in the aforementioned laminated structure preferably also contains elements or ions derived from the end-capping agent, or all layers may contain elements or ions derived from the end-capping agent.

[0093] In this specification, the element or ion derived from the capping agent (hereinafter also referred to as "capping element or ion") refers to the element or ion that caps the ends of the connecting bonds of the zirconia composite oxide in the zirconia composite sintered body composed of zirconia composite oxide, thereby weakening the strength of the crystal interface (hereinafter also referred to as "grain boundary") (hereinafter also referred to as "grain boundary strength").

[0094] End-capping agents can end at least a portion of the crystal boundaries.

[0095] "End capping" refers to the phenomenon where the target element or ion (end capping element or ion) replaces the aforementioned metal element and merges with the connecting bond of the zirconium oxide complex oxide at the crystal boundary.

[0096] It can be inferred that the capping elements or ions exist at the grain boundary in the form of +1 cations or -1 anions, thereby causing electrostatic repulsion between the capped cations or anions, thus weakening the grain boundary strength.

[0097] In addition, the contents of zirconium oxide, stabilizer, Nb2O5 and Ta2O5 in the zirconium oxide composite sintered body can also be determined by inductively coupled plasma (ICP) emission spectroscopy, fluorescence X-ray analysis and other methods.

[0098] The content (mol%) of elements or ions derived from the capping agent is the external addition rate relative to the total 100 mol% of zirconium oxide, the aforementioned stabilizer, Nb₂O₅, and Ta₂O₅. Therefore, the content (mol%) of elements or ions derived from the capping agent in the zirconium oxide composite sintered body can be calculated by converting the amount (mass) of raw materials added at the time of addition into mol%.

[0099] Furthermore, the content (mass%) of the zirconia reinforcing agent is an external addition rate relative to the total mass% of zirconia, the aforementioned stabilizer, Nb2O5, and Ta2O5. Therefore, the content (mass%) of the zirconia reinforcing agent in the zirconia composite sintered body can be calculated based on the amount (mass) of raw materials added at the time of addition.

[0100] The zirconia composite sintered body of the present invention has strength and light transmittance suitable for dental applications and high machinability. The reason why it can be machined in the sintered body state is still uncertain, but can be speculated as follows.

[0101] It can be inferred that in a zirconia composite sintered body containing zirconia, a stabilizer that can suppress the zirconia phase transformation, and containing Nb2O5 and / or Ta2O5, the presence of end-capping elements or ions at the crystal boundaries reduces the grain boundary strength in the form of +1 valent cations or -1 valent anions, acting in a direction that facilitates the separation of particles from each other, making it easier to cut and improving machinability.

[0102] End-capping elements or ions form +1 valent cations or -1 valent anions at the grain boundaries of the zirconia composite sintered body, which then bond with the linkage bonds present in the zirconia-based composite oxide. Through this bonding, the cations or anions electrostatically repel each other, maintaining the strength and light transmittance properties in the form of particles constituting the zirconia composite sintered body, while also weakening the grain boundary strength, thus improving machinability.

[0103] For example, it can be considered as a form in which a +1 valent cation replaces the aforementioned metal element and bonds with another linking bond of the oxygen atom of the metal element (e.g., Zr, Hf, Y, Nb, or Ta) contained in the zirconium oxide composite oxide.

[0104] Alternatively, it can be considered as OH2 bonded between -1 valent anions and metallic elements (such as Zr, Hf, Y, Nb, or Ta) contained in zirconium oxide composite oxides. + The form of bonding.

[0105] Furthermore, it can be considered as the form in which a -1 valent anion bonds to a cation of a metal element (such as Zr, Hf, Y, Nb, or Ta) that is bonded to other metal elements contained in a zirconium oxide composite oxide.

[0106] Furthermore, Nb₂O₅ and / or Ta₂O₅ in the zirconia composite sintered body function in a way that coarsens the microstructure and reduces hardness. Therefore, by integrating with the end-capping elements or ions and Nb₂O₅ and / or Ta₂O₅, they further improve machinability. Consequently, the end-capping elements or ions, integrated with Nb₂O₅ and / or Ta₂O₅, contribute to the strength necessary for artificial teeth and further enhance excellent rapid cutting performance. Thus, while reducing machining time, tool consumption can be reduced, and the number of dental repairs obtained through continuous machining using a single tool can be increased.

[0107] In the zirconia composite sintered body of the present invention, the end-capping elements or ions further improve machinability, acting as a rapid cutting aid as described above, thereby without significantly damaging strength and light transmittance.

[0108] When at least one of the multiple layers constituting the zirconia composite sintered body of the present invention is a layer that also contains elements or ions derived from the end-capping agent, the content of the end-capping element or ion contained in the aforementioned layer is preferably more than 0 mol% and less than 5 mol%. From the viewpoint of having better machinability in the sintered body state and being able to further increase the number of dental patches that can be continuously processed using a single processing tool, it is more preferably 0.05 mol% or more and less than 3 mol%, more preferably 0.06 mol% or more and less than 2.5 mol%, particularly preferably 0.07 mol% or more and less than 1.0 mol%, and most preferably 0.08 mol% or more and less than 0.34 mol%.

[0109] Furthermore, when the end-capping element or ion contained in the zirconia composite sintered body of the present invention is a Group 17 element or ion, from the viewpoint that the machinability in the sintered body state is better and the number of dental patches that can be continuously processed using a single processing tool can be further increased, it is more preferably 0.2 mol% or more and 5 mol% or less, more preferably 0.3 mol% or more and 4 mol% or less, particularly preferably 0.4 mol% or more and 3.5 mol% or less, and most preferably 0.5 mol% or more and 3.0 mol% or less.

[0110] Furthermore, in the stacked structure of a zirconia composite sintered body containing end-capping elements or ions, the content of end-capping elements or ions can be the same or different in all layers.

[0111] In this specification, "different content of end-capping elements or ions" means that when calculating the external addition rate of a specific layer relative to the total 100 mol% of zirconium oxide, the aforementioned stabilizer, Nb2O5, and Ta2O5, and when calculating the external addition rate of another specific layer relative to the total 100 mol% of zirconium oxide, the aforementioned stabilizer, Nb2O5, and Ta2O5, the content of end-capping elements or ions between the two specific layers is different.

[0112] In this specification, when the content of the end-capping element or ion is different, the difference in the content of the end-capping element or ion between layers is 0.01 mol% or more, preferably 0.02 mol% or more, more preferably 0.03 mol% or more, even more preferably 0.04 mol% or more, and particularly preferably 0.05 mol% or more.

[0113] Furthermore, the difference in the content of end-capping elements or ions between layers is preferably 3.0 mol% or less, more preferably 2.0 mol% or less, even more preferably 1.0 mol% or less, and particularly preferably 0.5 mol% or less.

[0114] Additionally, as a suitable embodiment, the following zirconia composite sintered body can be listed, which contains zirconia, a stabilizer, at least one selected from Nb₂O₅ or Ta₂O₅, and a capping element or ion, wherein the zirconia composite sintered body has multiple layers with different contents of Nb₂O₅ or Ta₂O₅ relative to the total molar amount of zirconia, the aforementioned stabilizer, Nb₂O₅, and Ta₂O₅. Along a straight line extending from one end of the aforementioned zirconia composite sintered body to the other end, from one end to the other end, the tendency of the content of Nb2O5 or Ta2O5 to increase or decrease relative to the total molarity of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5 does not change, and the content of capping elements or ions in each layer is different, and from one end to the other end, the tendency of the content of capping elements or ions to increase or decrease does not change.

[0115] Furthermore, from the viewpoint of superior machinability in the sintered state, the following zirconia composite sintered bodies can be listed, wherein the tendency for the increase or decrease of the content of end-capping elements or ions is reversed relative to the tendency for the content of Nb₂O₅ or Ta₂O₅ to increase or decrease. As specific examples, zirconia composite sintered bodies can be listed where the content of Nb₂O₅ or Ta₂O₅ tends to decrease, while the content of end-capping elements or ions tends to increase; and zirconia composite sintered bodies where the content of Nb₂O₅ or Ta₂O₅ tends to increase, while the content of end-capping elements or ions tends to decrease. From the viewpoint of particularly superior machinability in the sintered state, the following zirconia composite sintered bodies are preferred, wherein the content of Nb₂O₅ or Ta₂O₅ tends to decrease, while the content of end-capping elements or ions tends to increase.

[0116] In the aforementioned suitable embodiments, dental repairs that more closely resemble natural teeth in appearance can be obtained through the gradual change in light transmittance, and the machinability in the sintered state is superior.

[0117] Alternatively, as another suitable embodiment, the following zirconia composite sintered body can be listed, which contains zirconia, a stabilizer, at least one selected from Nb₂O₅ or Ta₂O₅, and a capping element or ion, wherein the zirconia composite sintered body has multiple layers with different contents of the stabilizer relative to the total molar amount of zirconia, the aforementioned stabilizer, Nb₂O₅, and Ta₂O₅. Along a straight line extending from one end of the aforementioned zirconia composite sintered body to the other end, from one end to the other end, relative to the total molarity of zirconia, the aforementioned stabilizer, Nb2O5, and Ta2O5, the tendency for the content of the aforementioned stabilizer to increase or decrease does not change, and the content of capping elements or ions in each layer is different, and from one end to the other end, the tendency for the content of capping elements or ions to increase or decrease does not change.

[0118] Furthermore, from the viewpoint of superior machinability in the sintered state, the following zirconia composite sintered bodies can be listed, wherein the tendency for the increase or decrease of the content of the aforementioned stabilizer is the same as the tendency for the increase or decrease of the content of the end-capping element or ion. Specific examples include: a zirconia composite sintered body in which the content of the aforementioned stabilizer tends to decrease, and in contrast, the content of the end-capping element or ion tends to decrease; and a zirconia composite sintered body in which the content of the aforementioned stabilizer tends to increase, and in contrast, the content of the end-capping element or ion tends to increase. From the viewpoint of particularly superior machinability in the sintered state, the following zirconia composite sintered body is preferred, wherein the content of the aforementioned stabilizer tends to increase, and in contrast, the content of the end-capping element or ion tends to increase.

[0119] In the aforementioned suitable embodiments, dental repairs that more closely resemble natural teeth in appearance can be obtained through the gradual change in light transmittance, and the machinability in the sintered state is superior.

[0120] As mentioned above, it is important that, from the viewpoint of demonstrating appropriate interaction between the potential point and the adsorption site at the grain boundary, the end-capping element or ion exists as a +1 valent cation or a -1 valent anion at the grain boundary.

[0121] As the end-capping element or ion, it is preferably an element or its ion belonging to the 2nd to 7th period of the periodic table and whose first ionization energy is smaller than that of the group 18 elements in the same period, an element or its ion with high electron affinity, nitrate ion, hypochlorite ion, chlorite ion, chlorate ion, perchlorate ion, bromate ion, permanganate ion, metaborate ion, or cyanide ion.

[0122] As a suitable embodiment, the following zirconia composite sintered body can be listed, wherein the aforementioned element or its ion derived from the capping agent is an element or its ion belonging to the 2nd to 7th period of the periodic table and whose first ionization energy is smaller than that of the group 18 elements of the same period, and / or an element or its ion with high electron affinity.

[0123] As elements belonging to the 2nd to 7th periods of the aforementioned periodic table and whose first ionization energy is smaller than that of the Group 18 elements in the same period, Cu, Ag, Li, Na, K, Rb, Cs, Fr, etc. can be appropriately listed from the viewpoint that it is easier to obtain +1 valent cations and that they have better machinability in the sintered state.

[0124] Elements with high electron affinity are preferred from the viewpoint that they are easier to obtain -1 valent anions and have better machinability in the sintered state. Preferred Group 17 elements are At, I, Br, Cl, and F.

[0125] The first ionization energy is the energy required to remove an electron from a neutral atom and ionize it. The first ionization energy can be set to the same level as that described in "Shriver-Atkins Inorganic Chemistry (Volume 1), 4th Edition, Part I: Fundamentals, 1. Atomic Structure". The first ionization energy can be converted to "kJ / mol" from the unit "eV" described in Appendix 2 of "Shriver-Atkins Inorganic Chemistry (Volume 1), 4th Edition", with 1 eV = 96.485 kJ / mol. The first ionization energy can also be determined by photoelectron yield spectroscopy (PYS).

[0126] Electron affinity (EA) is the energy released when an electron is introduced into a neutral atom. Electron affinity can be measured by the difference between ionization potential and energy gap. Ionization potential is defined as the energy difference between the highest-energy occupied orbital in a compound's molecular orbital and the vacuum level, and its value is determined using ultraviolet photoelectron spectroscopy.

[0127] As the first ionization energy and electron affinity, data stored in the NIST Chemistry WebBook (https: / / webbook.nist.gov / chemistry / ) can be used to select either ionization energy or electron affinity from ion energetics properties.

[0128] Regarding the first ionization energy and electron affinity, it is sufficient to compare the ease with which elements form +1 valent cations or -1 valent anions with other comparable elements, and the above methods can be appropriately used for the determination.

[0129] Specifically, Cu, Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl, and F can be listed as end-capping elements. From the viewpoint of further improving machinability, Cu, Ag, Li, Na, K, Rb, Cs, Fr, I, Br, Cl, and F are preferred.

[0130] In a suitable embodiment, the following zirconia composite sintered body can be listed, wherein the element derived from the capping agent includes at least one element selected from Cu, Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl and F, and the ion of the aforementioned element is at least one +1 cation or -1 anion selected from Cu, Ag, Li, Na, K, Rb, Cs, Fr, I, Br, Cl and F.

[0131] In another suitable embodiment, the following zirconia composite sintered body can be listed, wherein the element or ion derived from the capping agent includes at least one element or ion selected from Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl and F.

[0132] One type of capping element or ion can be used alone, or two or more can be used in combination.

[0133] As described above, the capping element or ion integrates with Nb2O5 and / or Ta2O5 and functions without impairing the effect of the aforementioned stabilizer. Therefore, the aforementioned stabilizer is not particularly limited and can achieve the effect of the present invention.

[0134] As mentioned above, Nb2O5 and Ta2O5 function in a way that coarsens the microstructure and reduces hardness. They can integrate with end-capping elements or ions and exert their effects, thus imparting excellent rapid machinability. Furthermore, through their interaction with other components added to the zirconia composite sintered body (such as TiO2 and Al2O3) and the application of HIP, the sintering density can be maximized, ensuring the aesthetics of natural teeth.

[0135] The content percentages of each of the aforementioned zirconium oxide, stabilizer, Nb₂O₅, and Ta₂O₅ components are proportions within a total of 100 mol% of zirconium oxide, stabilizer, Nb₂O₅, and Ta₂O₅, and the total of zirconium oxide, stabilizer, Nb₂O₅, and Ta₂O₅ does not exceed 100 mol%. For example, in the case where the raw material composition contains Nb₂O₅ but not Ta₂O₅, the content percentages of each of the zirconium oxide, stabilizer, and Nb₂O₅ components refer to the proportions relative to a total of 100 mol% of zirconium oxide, stabilizer, and Nb₂O₅.

[0136] Furthermore, when the content of the stabilizer is set to A mol%, and the total content of Nb2O5 and Ta2O5 is set to B mol%, in at least one of the aforementioned layers, from the viewpoint of machinability, the A / B ratio is preferably 0.9 or more and 3 or less, more preferably 0.95 or more and 2 or less. From the viewpoint of being able to impart better rapid cutting performance, suppress the consumption of machining tools, and further increase the number of dental repairs obtained by continuous machining using one machining tool, the A / B ratio is further preferably 1.0 or more and 1.7 or less.

[0137] As a suitable implementation, from the viewpoint of machinability, among the multiple layers constituting the zirconia composite sintered body of the present invention, it is preferable that at least the layers on the cut end side satisfy the aforementioned A / B ratio.

[0138] In any of the foregoing embodiments, when the layer containing elements or ions derived from the capping agent is within the aforementioned range of the A / B ratio, the effect of the capping elements or ions integrating with Nb2O5 and / or Ta2O5 and exerting their function is enhanced, resulting in superior machinability in the sintered state.

[0139] As a suitable embodiment of the present invention, the following zirconia composite sintered body is provided, which has a layered structure comprising zirconia, a stabilizer, and at least one selected from Nb2O5 or Ta2O5 in all layers. Relative to the total molar amounts of zirconium oxide, the aforementioned stabilizer, Nb₂O₅, and Ta₂O₅, The aforementioned layered structure comprises multiple layers with varying contents of at least one of the aforementioned stabilizer, Nb2O5, or Ta2O5. In a total of 100 mol% of zirconium oxide, the aforementioned stabilizer, Nb₂O₅, and Ta₂O₅ across all layers, The zirconium oxide content is 78~97.5 mol%. The aforementioned stabilizer contains 1-12 mol%. The combined content of Nb₂O₅ and Ta₂O₅ is 1~9 mol%. It also contains end-capping elements or ions. The aforementioned stabilizers include Y₂O₃ and / or CeO₂. The content of the aforementioned end-capping elements or ions is greater than 0 mol% and less than 5 mol% relative to the total 100 mol% of zirconium oxide, the aforementioned stabilizer, Nb2O5, and Ta2O5. When the content of the aforementioned stabilizer is set as A mol%, and the total content of Nb2O5 and Ta2O5 is set as B mol%, the ratio of A / B is 0.9 or higher and 3 or lower.

[0140] As one embodiment of the present invention, from the viewpoint of superior strength, the following zirconia composite sintered body can be cited, which contains zirconia, the aforementioned stabilizer, and at least one selected from Nb2O5 or Ta2O5. The zirconia composite sintered body comprises multiple layers having different contents of at least one of the aforementioned stabilizers, Nb2O5, or Ta2O5 relative to the total molar amounts of zirconia, the aforementioned stabilizers, Nb2O5, and Ta2O5. The zirconia composite sintered body, in addition to containing zirconia, the aforementioned stabilizer, Nb₂O₅ and / or Ta₂O₅, and end-capping elements or ions, also contains a zirconia reinforcing agent in at least one layer of the aforementioned laminated structure. Furthermore, from the viewpoint of particularly superior strength, zirconia composite sintered bodies in which the aforementioned zirconia reinforcing agent is contained in all layers of the aforementioned laminated structure can also be cited.

[0141] In a zirconia composite sintered body containing zirconia, the aforementioned stabilizer, and Nb2O5 and / or Ta2O5, the zirconia reinforcing agent can work together with the end-capping element or ion to improve the strength of the sintered body.

[0142] In zirconia composite sintered bodies containing zirconia reinforcing agents, as described above, the content of zirconia, the type and content of stabilizers, the total content of Nb2O5 and Ta2O5, the type and content of end-capping elements or ions, and the A / B ratio can be appropriately varied.

[0143] When at least one of the multiple layers constituting the zirconia composite sintered body is a layer containing a zirconia reinforcing agent, the content of the zirconia reinforcing agent contained in the aforementioned layer is preferably more than 0% by mass and less than 6.0% by mass relative to the total mass% of zirconia, the aforementioned stabilizer, and Nb2O5 and Ta2O5. From the viewpoint that it can be integrated and function effectively when combined with end-capping elements or ions, and has better strength, it is more preferably 0.01% by mass and less than 5.5% by mass, and even more preferably 0.5% by mass and less than 5.0% by mass.

[0144] Examples of zirconia reinforcing agents include TiO2 and Al2O3. These zirconia reinforcing agents can be used individually or in combination of two or more.

[0145] The content of the aforementioned zirconia reinforcing agent can be the same or different in all layers.

[0146] In this specification, "different content of zirconia reinforcing agent" means that when calculating the external addition rate of a specific layer relative to 100% by mass of the total of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5, and calculating the external addition rate of another specific layer relative to 100% by mass of the total of zirconia, the aforementioned stabilizer, Nb2O5 and Ta2O5, the content of zirconia reinforcing agent between the aforementioned specific layer and the specific other layer is different.

[0147] In this specification, when the content of the zirconia reinforcing agent is different, the difference in the content of the zirconia reinforcing agent between layers is 0.05% by mass or more, preferably 0.08% by mass or more, more preferably 0.09% by mass or more, even more preferably 0.10% by mass or more, and particularly preferably 0.11% by mass or more.

[0148] Furthermore, the difference in the content of the zirconium oxide reinforcing agent between layers is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, even more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less.

[0149] As a suitable embodiment, the following zirconia composite sintered body can be listed, wherein the zirconia reinforcing agent includes TiO2, and the content of TiO2 is 0.6 to 4.5% by mass relative to the total 100% by mass of zirconia, the aforementioned stabilizer, and Nb2O5 and Ta2O5.

[0150] As a suitable embodiment, the following zirconia composite sintered body can be listed, which contains zirconia, a stabilizer, at least one selected from Nb2O5 or Ta2O5, and a capping element or ion. The zirconia composite sintered body comprises multiple layers having different contents of at least one of the aforementioned stabilizers, Nb2O5, or Ta2O5 relative to the total molar amounts of zirconia, the aforementioned stabilizers, Nb2O5, and Ta2O5. In a total of 100 mol% of zirconium oxide, the aforementioned stabilizer, Nb₂O₅, and Ta₂O₅, The zirconium oxide content is 78~97.5 mol%. The aforementioned stabilizer contains 1-12 mol%. The combined content of Nb₂O₅ and Ta₂O₅ is 1~9 mol%. The aforementioned stabilizers include Y₂O₃ and / or CeO₂. The aforementioned zirconia reinforcing agent contains TiO2, and the content of TiO2 relative to the total mass% of zirconia, the aforementioned stabilizer, and Nb2O5 and Ta2O5 is 0.6~4.5% by mass. The content of the aforementioned end-capping elements or ions is greater than 0 mol% and less than 5 mol% relative to the total 100 mol% of zirconium oxide, the aforementioned stabilizer, Nb2O5, and Ta2O5. When the content of the aforementioned stabilizer is set as A mol%, and the total content of Nb2O5 and Ta2O5 is set as B mol%, the ratio of A / B is 0.9 or higher and 3 or lower.

[0151] The average grain size of the zirconia composite sintered body of the present invention is preferably 0.5 to 5.0 μm, more preferably 0.5 to 4.5 μm from the viewpoint of superior machinability, strength and light transmittance, and even more preferably 1.0 to 4.0 μm. The method for measuring the average grain size is as described in the examples described later.

[0152] The average grain size can be determined by adjusting the number of particles in an SEM image with a field of view of about 50, 100, 200, 500 or 1000 particles in the method described in the examples.

[0153] Regarding the density of zirconia composite sintered bodies, considering that higher density results in fewer internal voids, less light scattering, improved light transmittance, and increased strength, a density of 5.5 g / cm³ is preferred. 3 The above, more preferably 5.7 g / cm³ 3 The above is further optimized to be 5.9 g / cm³. 3 above.

[0154] Zirconia composite sintered bodies are particularly preferred as they are essentially void-free.

[0155] The density of a composite sintered body can be calculated as (mass of the composite sintered body) / (volume of the composite sintered body).

[0156] As a method for manufacturing the zirconia composite sintered body of the present invention, examples include the following method, which includes: a step of using a raw material composition to form a molded body, and a step of sintering the molded body. The aforementioned molded article has a laminated structure containing zirconium oxide, a stabilizer, and at least one selected from Nb2O5 or Ta2O5 in all layers. Relative to the total molar amounts of zirconium oxide, the aforementioned stabilizer, Nb₂O₅, and Ta₂O₅, The aforementioned layered structure comprises multiple layers with different contents of at least one of the aforementioned stabilizers, Nb2O5, or Ta2O5.

[0157] In manufacturing the molded body, a molded body having a target laminated structure can be obtained by using a raw material composition containing zirconium oxide, a stabilizer, and at least one selected from Nb2O5 or Ta2O5, and by adjusting the content of the components in a manner that differs in the content of at least one of the aforementioned stabilizer, Nb2O5, or Ta2O5.

[0158] The raw material composition of the zirconia composite sintered body includes zirconia, a stabilizer capable of inhibiting the zirconia phase transformation and contains Nb2O5 and / or Ta2O5, and may include a capping agent if necessary.

[0159] By including the capping agent in the aforementioned raw material composition, the machinability obtained by adding at least one of Nb2O5 or Ta2O5 can be further significantly improved.

[0160] The raw material composition for the zirconia composite sintered body can be in a dry state, or in a state containing liquid, or contained in liquid. The raw material composition can be in the form of, for example, powder, granules or pellets, paste, slurry, etc.

[0161] In embodiments where the resulting zirconia composite sintered body contains a capping element or ion, the raw material composition includes a capping agent. The capping agent is not particularly limited to any compound capable of forming a monovalent ion (+1-valent cation or -1-valent anion) in a solvent containing water; examples include hydroxides, salts, halides (fluorides, chlorides, bromides, iodides), cyanides, etc., containing elements or ions derived from the capping agent. One capping agent may be used alone, or two or more may be used in combination.

[0162] Examples of hydroxides containing end-capping elements or ions include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide.

[0163] Examples of salts containing end-capping elements or ions include carbonates, bicarbonates, nitrates, hypochlorites, chlorites, chlorates, perchlorates, bromates, permanganates, metaborates, sulfide salts, and cyanides.

[0164] Examples of carbonates containing end-capping elements or ions include lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, francium carbonate, and cesium carbonate.

[0165] Examples of bicarbonates containing end-capping elements or ions include lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, francium bicarbonate, and cesium bicarbonate.

[0166] Examples of nitrates containing end-capping elements or ions include calcium nitrate, strontium nitrate, ferric nitrate (II), ferric nitrate (III), cobalt nitrate (II), magnesium nitrate, gallium nitrate, yttrium nitrate (III), lanthanum nitrate (III), praseodymium nitrate, neodymium nitrate (III), manganese nitrate (II), europium nitrate, copper nitrate (II), thorium nitrate, aluminum nitrate, nickel nitrate (II), chromium nitrate (III), titanium nitrate (IV), zirconium nitrate, zirconium oxynitrate (IV) hydrate (ZrO(NO3)2·xH2O), cerium nitrate (III), tin nitrate, bismuth nitrate (III), scandium nitrate (III), indium nitrate (III), and hafnium nitrate (IV).

[0167] Examples of hypochlorites containing end-capping elements or ions include sodium hypochlorite and calcium hypochlorite.

[0168] Examples of chlorites containing end-capping elements or ions include sodium chlorite, potassium chlorite, lithium chlorite, calcium chlorite, magnesium chlorite, barium chlorite, copper(II) chlorite, copper(III) chlorite, silver chlorite, and nickel chlorite.

[0169] Examples of chlorates containing end-capping elements or ions include calcium chlorate, barium chlorate, cobalt chlorate, nickel chlorate, magnesium chlorate, zinc chlorate, and copper chlorate.

[0170] Examples of perchlorates containing end-capping elements or ions include iron(III) perchlorate, barium perchlorate, calcium perchlorate, cobalt perchlorate, nickel perchlorate, magnesium perchlorate, beryllium perchlorate, aluminum perchlorate, and cerium perchlorate.

[0171] Examples of bromates containing end-capping elements or ions include neodymium bromate, lanthanum bromate, and praseodymium bromate.

[0172] Examples of permanganate salts containing end-capping elements or ions include calcium permanganate (VII), potassium permanganate (VII), and sodium permanganate (VII).

[0173] Examples of metaborates containing end-capping elements or ions include sodium metaborate and barium metaborate.

[0174] Examples of sulfide salts containing end-capping elements or ions include copper sulfide (I).

[0175] Examples of cyanide salts containing end-capping elements or ions include barium cyanide, sodium cyanide, potassium cyanide, and calcium cyanide.

[0176] Examples of fluorides containing end-capping elements or ions include lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, cesium fluoride, francium fluoride, beryllium fluoride, magnesium fluoride, calcium fluoride, strontium fluoride, barium fluoride, scandium(III) fluoride, yttrium(III) fluoride, lanthanum(III) fluoride, cerium(III) fluoride, neodymium(III) fluoride, titanium(III) fluoride, titanium(IV) fluoride, zirconium(IV) fluoride, hafnium(IV) fluoride, tantalum(V) fluoride, manganese(II) fluoride, manganese(III) fluoride, iron(II) fluoride, iron(III) fluoride, copper(II) fluoride, zinc(II) fluoride, aluminum fluoride, chromium(III) fluoride, bismuth(III) fluoride, indium(III) fluoride, and tin(II) fluoride.

[0177] Examples of chlorides containing end-capping elements or ions include zirconium oxychloride, lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride, francium chloride, beryllium chloride, magnesium chloride, calcium chloride, strontium chloride, barium chloride, scandium(III) chloride, yttrium(III) chloride, lanthanum(III) chloride, cerium(III) chloride, praseodymium chloride, neodymium(III) chloride, samarium chloride, europium chloride, titanium(III) chloride, titanium(IV) chloride, zirconium(IV) chloride, hafnium(IV) chloride, tantalum(V) chloride, manganese chloride, ferric chloride(II), ferric chloride(III), cobalt(II) chloride, nickel(II) chloride, copper(I) chloride, copper(II) chloride, zinc(II) chloride, aluminum chloride, gallium chloride, bismuth(III) chloride, indium(I) chloride, indium(III) chloride, tin(II) chloride, etc.

[0178] Examples of bromides containing end-capping elements or ions include lithium bromide, sodium bromide, potassium bromide, rubidium bromide, cesium bromide, francium bromide, beryllium bromide, magnesium bromide, calcium bromide, strontium bromide, barium bromide, scandium (III) bromide, yttrium (III) bromide, cerium (III) bromide, neodymium (III) bromide, titanium (IV) bromide, zirconium (IV) bromide, tantalum (V) bromide, manganese (II) bromide, iron (II) bromide, iron (III) bromide, cobalt (II) bromide, nickel (II) bromide, copper (I) bromide, copper (II) bromide, zinc (II) bromide, chromium (III) bromide, bismuth (III) bromide, vanadium (III) bromide, indium (III) bromide, and tin bromide.

[0179] Examples of iodides that contain end-capped elements or ions include lithium iodide, sodium iodide, potassium iodide, rubidium iodide, cesium iodide, francium iodide, beryllium iodide, calcium iodide, magnesium iodide, strontium iodide, barium iodide, scandium (III) iodide, yttrium (III) iodide, lanthanum (III) iodide, cerium (III) iodide, neodymium (III) iodide, titanium (IV) iodide, zirconium (IV) iodide, hafnium (IV) iodide, tantalum (V) iodide, manganese (II) iodide, iron (II) iodide, iron (III) iodide, cobalt (II) iodide, nickel (II) iodide, copper (I) iodide, zinc (II) iodide, aluminum iodide, chromium (III) iodide, vanadium (II) iodide, bismuth (III) iodide, indium (III) iodide, tin (II) iodide, and tin (IV) iodides.

[0180] For zirconium oxide, commercially available zirconium oxide powder can be used.

[0181] Commercially available products include, for example, zirconium oxide powder (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%), "TZ-10YS" (Y2O3 content: 10 mol%), and "TZ-3Y-E" (Y2O3 content: 3 mol%). The aforementioned commercially available zirconium oxide powders include HfO2, and can also contain substances containing Y2O3. These commercially available products include "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%), and "TZ-0" (Y2O3 content: 0 mol%). (These are manufactured by Tosoh Corporation).

[0182] As zirconium oxide powder, the raw material composition of the present invention can use zirconium oxide powder with Y2O3 uniformly dispersed in the TZ series (part of the trade name includes "TZ") of the aforementioned commercially available products.

[0183] There are no particular limitations on the manufacturing method of zirconia powder. Well-known methods such as the break-down process of pulverizing coarse particles into micronized powder and the building-up process of synthesizing from atoms or ions using nucleation and growth processes can be used.

[0184] The type of zirconia powder in the aforementioned raw material composition is not particularly limited. If the zirconia powder contains zirconia but no stabilizer, or if the stabilizer content is increased as needed, stabilizer particles may be added separately. Regarding the stabilizer particles, there are no particular limitations as long as they can adjust the stabilizer content in the zirconia composite sintered body to the aforementioned specified range.

[0185] Stabilizer particles can be, for example, commercially available products, or commercially available powders can be pulverized using known pulverizing and mixing equipment (ball mill, etc.) before use.

[0186] Regarding the aforementioned stabilizers, both stabilizers not dissolved in zirconium oxide and stabilizers dissolved in zirconium oxide can be used.

[0187] In a suitable embodiment, from the viewpoint of making it easy to obtain the desired zirconia composite sintered body in the aforementioned raw material composition, a method for manufacturing the zirconia composite sintered body can be described, wherein the stabilizer (suitably Y2O3) comprises a stabilizer not dissolved in zirconia. The presence of a stabilizer not dissolved in zirconia can be confirmed by, for example, X-ray diffraction (XRD) patterns.

[0188] When a peak originating from a stabilizer is identified in the XRD pattern of the raw material composition or the molded body, it indicates the presence of a stabilizer that is not dissolved in zirconium oxide in the raw material composition or the molded body.

[0189] When the stabilizer is completely dissolved in zirconium oxide, peaks originating from the stabilizer are generally not detectable in the XRD pattern. However, depending on factors such as the crystallization state of the stabilizer, even if no stabilizer peaks are found in the XRD pattern, the stabilizer may not be dissolved in zirconium oxide at all.

[0190] Regarding the case where the stabilizer includes a stabilizer that does not undergo solid solution relative to zirconium oxide, the following explanation will be given using yttrium oxide as an example.

[0191] The presence rate f of yttrium trioxide (hereinafter sometimes referred to as "undissolved yttrium trioxide") in the raw material composition or molded article of the present invention is... y The calculation can be performed according to the following mathematical formula (1). f y =I 29 / (I 28 +I 29 +I 30 )×100 (1) (where f) y The percentage (%) of unsolvable yttrium trioxide in XRD determination is represented by I. 28 I represents the area intensity of the peak near 2θ=28° where the main peak of the monoclinic crystal system appears. 29 I represents the area intensity of the peak near 2θ=29° where the main peak of yttrium trioxide appears. 30 This represents the area intensity of the peak near 2θ=30° where the main peak appears in a tetragonal or cubic crystal system.

[0192] In addition, when using stabilizers other than yttrium trioxide in combination, the peak of other stabilizers can be substituted to replace I. 29 This can also be applied to calculate the unsolvable content of stabilizers other than yttrium trioxide.

[0193] From the perspective of easily obtaining the target zirconia composite sintered body, the presence rate f of undissolved yttrium oxide is... y Preferably greater than 0%, more preferably 1% or more, further preferably 2% or more, and particularly preferably 3% or more. The presence rate f of undissolved yttrium trioxide. y The upper limit can be, for example, below 25%, depending on the content of yttrium oxide in the raw material composition or the molded body.

[0194] For example, when the content of yttrium oxide in the raw material composition or molded article of the present invention is 3 mol% or more and 8 mol% or less, it is as follows.

[0195] When the yttrium trioxide content is 3 mol% or more and less than 4.5 mol%, f y It can be set to below 15%. When the yttrium trioxide content is above 4.5 mol% and below 5.8 mol%, f y It can be set to below 20%. When the yttrium trioxide content is above 5.8 mol% and below 8 mol%, f y It can be set to below 25%.

[0196] For example, when the yttrium trioxide content is above 3 mol% and below 4.5 mol%, f y Preferably, it is 2% or more, more preferably 3% or more, even more preferably 4% or more, and particularly preferably 5% or more.

[0197] When the yttrium trioxide content is above 4.5 mol% and below 5.8 mol%, f y Preferably, it is 3% or more, more preferably 4% or more, even more preferably 5% or more, even more preferably 6% or more, and particularly preferably 7% or more.

[0198] When the yttrium trioxide content is above 5.8 mol% and below 8 mol%, f y Preferably, it is 4% or more, more preferably 5% or more, even more preferably 6% or more, even more preferably 7% or more, and particularly preferably 8% or more.

[0199] In the raw material composition or molded article of the present invention, not all of the aforementioned stabilizers may be completely dissolved in zirconium oxide. It should be noted that, in the present invention, the solid solution of the stabilizer means, for example, that the elements (atoms) contained in the stabilizer are dissolved in zirconium oxide.

[0200] The Nb2O5 and / or Ta2O5 added to the raw material composition of the present invention are not particularly limited, as long as they can adjust the content of Nb2O5 and / or Ta2O5 in the zirconia composite sintered body to the aforementioned specified range. There are no particular limitations on the Nb2O5 and / or Ta2O5; for example, commercially available products can be used, or the powder of commercially available products can be pulverized using a known pulverizing and mixing device (ball mill, etc.) before use.

[0201] As a step in preparing the raw material composition, examples include the following method: wet mixing of each raw material of the aforementioned raw material composition (zirconia, stabilizer, Nb2O5 and / or Ta2O5, end-capping agent as needed (e.g., a compound that can form a monovalent ion in a solvent containing water), and further, zirconia reinforcing agent as needed) in a solvent containing water to obtain the raw material composition.

[0202] There is no particular limitation on the method of wet mixing the aforementioned raw materials in a solvent containing water. For example, the raw materials can be wet-mixed using a known pulverizing and mixing device (ball mill, etc.) to form a slurry, and then the slurry can be dried and granulated to produce a granular raw material composition.

[0203] In the wet mixing process, additives such as binders, plasticizers, dispersants, emulsifiers, defoamers, pH adjusters, and lubricants may also be included. Each additive may be used individually or in combination of two or more.

[0204] After a slurry is prepared by adding a mixture of zirconium oxide, Y2O3, Nb2O5, and / or Ta2O5 with a capping agent as required to water, the aforementioned binder may be subsequently added to the pulverized slurry.

[0205] The aforementioned adhesive is not particularly limited and known materials may be used. Examples of adhesives include polyvinyl alcohol-based adhesives, acrylic adhesives, wax-based adhesives (paraffin wax, etc.), methylcellulose, carboxymethylcellulose, polyvinyl butyral, polymethyl methacrylate, ethylcellulose, polyethylene, polypropylene, ethylene vinyl acetate copolymer, polystyrene, atactic polypropylene, and methacrylic resins.

[0206] Examples of plasticizers include polyethylene glycol, glycerin, propylene glycol, and dibutyl phthalate.

[0207] 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.

[0208] Examples of emulsifiers include alkyl ethers, phenyl ethers, and sorbitol derivatives.

[0209] Examples of defoaming agents include alcohols, polyethers, silicones, and waxes.

[0210] Examples of pH adjusters include ammonia and ammonium salts (including ammonium hydroxide such as tetramethylammonium hydroxide).

[0211] Examples of lubricants include polyoxyethylene alkyl ethers and waxes.

[0212] As a solvent used in wet mixing, there are no particular limitations as long as it contains water. Organic solvents, mixtures of water and organic solvents, or water alone can be used. Examples of organic solvents include ketone solvents such as acetone and ethyl methyl ketone; alcohol solvents such as ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, glycerol, diglycerol, polyglycerol, propylene glycol, dipropylene glycol, polypropylene glycol, ethylene glycol, diethylene glycol, polyethylene glycol, polyethylene glycol monomethyl ether, 1,2-pentanediol, 1,2-hexanediol, and 1,2-octanediol.

[0213] The raw material composition of the zirconia composite sintered body used in this invention can contain other components besides zirconia, Y₂O₃, Nb₂O₅, Ta₂O₅, and, as needed, end-capping agents and zirconia reinforcing agents, as long as the effects of this invention are achieved. Examples of these other components include, for instance, colorants (pigments and composite pigments), fluorescent agents, and SiO₂. Other components can be used individually or in combination of two or more.

[0214] Examples of pigments include oxides of at least one element selected from V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, Tb, and Er (specifically, NiO, Cr2O3, etc.), preferably oxides of at least one element selected from V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Pr, Sm, Eu, Gd, and Tb, and more preferably oxides of at least one element selected from V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Tb. Y2O3 and CeO2 can be excluded from the pigments.

[0215] Examples of composite pigments mentioned above include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, and (Co,Zn)Al2O4.

[0216] Examples of fluorescent agents mentioned above include Y₂SiO₅:Ce, Y₂SiO₅:Tb, (Y,Gd,Eu)BO₃, Y₂O₃:Eu, YAG:Ce, ZnGa₂O₄:Zn, and BaMgAl. 10 O 17 Eu et al.

[0217] Next, the obtained raw material composition is molded to produce a molded body. There are no particular limitations on the molding method; known methods (such as pressure molding) can be used.

[0218] When manufacturing zirconia molded bodies using a method that includes a step of pressurizing a raw material composition, the specific method of pressurization is not particularly limited, and a known pressurization machine can be used. Examples of specific pressurization methods include uniaxial pressurization.

[0219] The pressure applied during compression molding is appropriately set to an optimal value based on the target dimensions of the molded body, open porosity, biaxial bending strength, and particle size of the raw material powder; typically, it is 5 MPa or higher and 1000 MPa or lower. By increasing the pressure applied during molding in the aforementioned manufacturing method, the pores of the resulting molded body are further filled, allowing for a lower open porosity and increased density. Furthermore, to further increase the density of the resulting zirconia molded body, cold isostatic pressing (CIP) can be performed after uniaxial pressing.

[0220] Next, the resulting molded body is sintered to obtain a zirconia composite sintered body.

[0221] The sintering temperature (maximum sintering temperature) for sintering the molded body to obtain the zirconia composite sintered body is preferably, for example, 1300°C or higher, more preferably 1350°C or higher, even more preferably 1400°C or higher, even more preferably 1450°C or higher, and particularly preferably 1500°C or higher. Furthermore, this sintering temperature is preferably, for example, 1680°C or lower, more preferably 1650°C or lower, and even more preferably 1600°C or lower. As a method for manufacturing the zirconia composite sintered body of the present invention, it preferably includes a step of sintering the molded body at a maximum sintering temperature of 1300 to 1680°C. The aforementioned maximum sintering temperature is preferably an atmospheric temperature.

[0222] The holding time (retention time) at the highest sintering temperature varies with temperature, and is preferably 30 hours or less, more preferably 20 hours or less, further preferably 10 hours or less, even more preferably 5 hours or less, particularly preferably 3 hours or less, and most preferably 2 hours or less. Furthermore, this holding time can also be set to 25 minutes or less, 20 minutes or less, or 15 minutes or less. Additionally, this holding time is preferably 1 minute or more, more preferably 5 minutes or more, and further preferably 10 minutes or more. According to the manufacturing method of the present invention, based on the stabilizer content, it is possible to produce a zirconia composite sintered body with excellent flexural strength, light transmittance, and machinability in the sintered state. Furthermore, the sintering time can be shortened as long as the effects of the present invention are achieved. By shortening the sintering time, production efficiency can be improved and energy costs reduced.

[0223] In the method for manufacturing the zirconia composite sintered body of the present invention, when sintering the aforementioned molded 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-mentioned lower limit or above, productivity is improved.

[0224] The sintering process for the aforementioned molded body can be performed using a general dental zirconia sintering furnace. Commercially available zirconia sintering 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.).

[0225] Furthermore, the sintering process for the molded body preferably includes a hot isostatic pressing (HIP) treatment process in addition to sintering at the aforementioned highest sintering temperature. HIP treatment can further improve the light transmittance and strength of the zirconia composite sintered body.

[0226] Hereinafter, the sintered body obtained by sintering at the aforementioned highest sintering temperature 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".

[0227] HIP processing can be performed using a known hot isostatic pressing (HIP) apparatus.

[0228] The temperature of HIP treatment is not particularly limited. However, from the perspective of obtaining a high-strength and dense zirconia composite sintered body, the HIP temperature is preferably 1200°C or higher, more preferably 1300°C or higher, and even more preferably 1400°C or higher. In addition, the HIP temperature is preferably 1700°C or lower, more preferably 1650°C or lower, and even more preferably 1600°C or lower.

[0229] In the method for manufacturing the zirconia composite sintered body of the present invention, when performing HIP treatment on the aforementioned primary sintered body, the HIP pressure is not particularly limited. From the perspective of obtaining a sintered body with high strength and density, the HIP pressure is preferably 100 MPa or more, more preferably 125 MPa or more, and even more preferably 130 MPa or more. In addition, 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, and even 200 MPa or less.

[0230] In the method for manufacturing the zirconia composite sintered body of the present invention, 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-mentioned lower limit or above, productivity is improved.

[0231] In the method for manufacturing the zirconia composite sintered body of the present invention, when performing HIP treatment on the aforementioned primary sintered body, the HIP time is not particularly limited. However, from the perspective of obtaining a zirconia composite sintered body with high strength and density, the HIP treatment time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. Furthermore, the HIP treatment time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 3 hours or less.

[0232] In the method for manufacturing the zirconia composite sintered body 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 mixture, air, and inactive gases (such as nitrogen, argon, etc.).

[0233] 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 greater than 0% and less than 20%.

[0234] 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.

[0235] In the method for manufacturing the zirconia composite sintered body of the present invention, if the aforementioned HIP treatment is carried out in a reducing atmosphere using an inactive gas or the like, blackening may sometimes occur due to oxygen defects. In this case, to remove the blackening, after the aforementioned HIP treatment step, it is preferable to include a heat treatment step (hereinafter also referred to as "tempering treatment") at 1650°C or below in the atmosphere or in an oxygen-excess atmosphere. From the viewpoint of effectively carrying out heat treatment, it is more preferable to carry it out in an oxygen-excess atmosphere. "Oxygen-excess atmosphere" refers to an oxygen concentration greater 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%.

[0236] In the method for manufacturing the zirconia composite sintered body of the present invention, the light transmittance can also be adjusted by appropriately adjusting various conditions in the aforementioned HIP treatment. For example, by lowering the heat treatment temperature, the light transmittance can be actively reduced. Therefore, by adjusting components such as reducing light transmittance in the layer corresponding to the tooth neck and increasing light transmittance in the layer corresponding to the cut end, and by adjusting various conditions in the HIP treatment, the desired light transmittance can also be adjusted in each layer.

[0237] The zirconia composite 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.

[0238] As a suitable implementation method, the following zirconia composite sintered body, which is a sintered body after tempering treatment, can be listed.

[0239] Depending on the aesthetics of the zirconia composite sintered body (e.g., the color of dental patch), the heat treatment temperature in the atmosphere or in an oxygen-rich atmosphere can be appropriately adjusted.

[0240] In a suitable embodiment, from the viewpoint of the aesthetics of the zirconia composite 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.

[0241] In other suitable embodiments, from the viewpoint of the aesthetics of the zirconia composite 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.

[0242] Furthermore, in any embodiment, the temperature of the heat treatment is preferably 500°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher.

[0243] The aforementioned tempering process can be performed using a standard dental zirconia sintering furnace. Commercially available zirconia sintering 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.).

[0244] Although the zirconia composite sintered body of the present invention is a sintered body, its machinability is still excellent. Therefore, it is not necessary to machine the composite pre-sintered body in a semi-sintered state in a blank state and then sinter it to make a sintered body.

[0245] On the other hand, the manufacturing method of the zirconia composite sintered body can also be set as follows: the molded body obtained by using the aforementioned raw material composition is pre-fired to produce a composite pre-fired body in a semi-sintered state, and the unprocessed composite pre-fired body is mechanically processed to produce a sintered body.

[0246] As another embodiment, a method for manufacturing a zirconia composite sintered body can be described, which includes: a step of using the aforementioned raw material composition to make a molded body; a step of pre-firing the obtained molded body to obtain a zirconia composite pre-fired body (pre-firing step); and a step of sintering the zirconia composite pre-fired body.

[0247] In order to reliably achieve block formation, the firing temperature (pre-firing temperature) in the pre-firing process is preferably 800°C or higher, more preferably 900°C or higher, and even more preferably 950°C or higher.

[0248] Furthermore, the pre-firing temperature is preferably 1200°C or lower, more preferably 1150°C or lower, and even more preferably 1100°C or lower. For example, a pre-firing temperature of 800°C to 1200°C is preferred. It can be assumed that with such a pre-firing temperature, the solidification of the stabilizer will not occur significantly during the pre-firing process.

[0249] The density of the zirconia composite pre-sintered body is preferably 2.7 g / cm³. 3 That's all. Additionally, the preferred density of the zirconia composite pre-sintered body is 4.0 g / cm³. 3 The preferred value is 3.8 g / cm³. 3 The following is a further preferred value: 3.6 g / cm³3 The following applies. Within this density range, processing is readily possible. The density of the composite pre-fired body can be calculated, for example, in the form of (mass of the composite pre-fired body) / (volume of the composite pre-fired body).

[0250] In addition, the three-point bending strength of the zirconia composite pre-sintered body is preferably 15~70 MPa, more preferably 18~60 MPa, and even more preferably 20~50 MPa.

[0251] The aforementioned bending strength can be measured using a test piece with a thickness of 5 mm × width of 10 mm × length of 50 mm, according to ISO 6872:2015, except for the dimensions of the test piece. The test piece's front and C-side (the surface obtained by chamfering the corners of the test piece at a 45° angle) are finished along their length using 600-grit sandpaper. The test piece is positioned with its widest face facing the vertical direction (load direction). In the bending test, the span is set to 30 mm, and the slider speed is set to 1.0 mm / min.

[0252] The sintering process for the zirconia composite pre-sintered body can be carried out using the same methods and conditions (temperature, pressure, etc.) as the sintering process for the aforementioned molded body. Therefore, in embodiments of the manufacturing method using the zirconia composite pre-sintered body, the term "molded body" can also be understood as "composite pre-sintered body".

[0253] The zirconia composite sintered body of the present invention exhibits excellent strength. The biaxial flexural strength of the zirconia composite sintered body of the present invention is preferably 300 MPa or more, more preferably 350 MPa or more, further preferably 400 MPa or more, even more preferably 450 MPa or more, and particularly preferably 500 MPa or more. By giving the zirconia composite sintered body of the present invention this biaxial flexural strength, it is possible to suppress fractures in the oral cavity when used, for example, as a dental restoration. There is no particular upper limit to this biaxial flexural strength; for example, it can be set to 1200 MPa or less, and further, to 1000 MPa or less. It should be noted that the biaxial flexural strength of the zirconia composite sintered body can be measured according to ISO 6872:2015.

[0254] The zirconia composite sintered body of the present invention preferably has high light transmittance. Light transmittance can be measured using ΔL... * (WB) is used for evaluation.

[0255] Regarding light transmittance, specifically, in each layer of the stacked structure constituting the zirconia composite sintered body of the present invention, the ΔL of a sample with a diameter of 15 mm and a thickness of 1.2 mm... * The value of (WB) is preferably 10 or more, more preferably 11 or more, even more preferably 12 or more, and particularly preferably 13 or more.

[0256] If the ΔL * (WB) Within the range described above, by having multiple layers with different contents of at least one of the stabilizer, Nb2O5, or Ta2O5, it is possible to obtain a gradient of light transmittance between the layers, which is sufficient for a gradient of light transmittance compared to natural teeth, thereby obtaining a zirconia composite sintered body with high aesthetics that is closer to natural teeth.

[0257] ΔL * (WB) refers to the difference between the lightness (first L* value) of the same sample against a white background and its lightness (second L* value) against a black background. Specifically, it refers to the difference between the L* value against a white background (JIS Z 8781-4:2013 Colorimetry - Part 4: CIE 1976 L*a*b* color space) and the L* value against a black background. The white background refers to the white portion of the opacity test paper described in Section 1 of Part 4 of JIS K 5600-4-1:1999, and the black background refers to the black portion of the aforementioned opacity test paper.

[0258] ΔL * There is no specific upper limit for (WB), such as below 25. From an aesthetic point of view, it can be set to below 20.

[0259] It should be noted that the ΔL* of the zirconia composite sintered body with a diameter of 15 mm and a thickness of 1.2 mm can be measured using a spectrophotometer. For example, it can be measured using a dental colorimeter ("CrystalEye CE100-CE / JP", 7-band LED light source, and analysis software "CrystalEye" (manufactured by Olympus Corporation)).

[0260] Dental restorations manufactured using the zirconia composite sintered body of the present invention include, for example, inlays, onlays, veneers, crowns, core-integrated crowns, and bridges, as well as abutment teeth, dental supports, dentures, denture beds, and implant components (fixtures, abutments), etc. Furthermore, machining is preferably performed using, for example, a commercially available dental CAD / CAM system. Examples of such CAD / CAM systems include the CEREC system manufactured by Dentsply Sirona Dental Systems and the "KATANA (registered trademark) system" manufactured by Kuraray Noritake Dental Co., Ltd.

[0261] In addition, the zirconia composite sintered body of the present invention can also be used for purposes other than dental applications, and is particularly suitable for zirconia components that require irregular to complex shapes and strength.

[0262] Compared to sintered bodies manufactured using only existing manufacturing methods (injection molding, CIP, casting, or 3D printing, etc.), the zirconia composite sintered body of the present invention allows for direct processing of the sintered body. Therefore, it is economical when desired zirconia components can be obtained in a short time, and in cases of complex-shaped parts that are difficult to manufacture using conventional methods, it eliminates the need for mechanical fitting to obtain multiple components, thus enabling the production of zirconia components that maintain high strength. Furthermore, since the sintered body can be processed directly, a sintering process is unnecessary when dimensional accuracy is required, and there is no uneven firing shrinkage, thus enabling the production of zirconia components with high precision. Specifically, it can also be used as a method for manufacturing components for jewelry and accessories, engine and interior components for mobile bodies such as aircraft and automobiles, frame materials for display panels, building components, components for electrochemical products, components for household goods, and toy parts.

[0263] Alternatively, this zirconia component can be combined with different materials to be used as a composite component.

[0264] The present invention includes any implementation that achieves the effects of the present invention by combining all or part of the above-described structures and implementation methods within the scope of the technical concept of the present invention. Example

[0265] The following examples illustrate the present invention in more detail, but the present invention is not limited to these examples at all. Those skilled in the art can make various modifications within the scope of the technical concept of the present invention.

[0266] It should be noted that in the following examples and comparative examples, the average particle size refers to the average primary particle size, which can be determined by laser diffraction scattering. Specifically, a laser diffraction / scattering particle size distribution measuring device (Partica LA-950: manufactured by Horiba Corporation) can be used to irradiate the water-diluted slurry with ultrasound for 30 minutes, and then the particle size is measured according to a volume basis while irradiating with ultrasound.

[0267] [Examples 1-11 and Comparative Examples 1-2] The test samples of each embodiment and comparative example were prepared by a process involving the preparation of a granular raw material composition, the preparation of a molded body, and the preparation of a zirconia composite sintered body (preparation of a single sintered body, HIP treatment, and tempering treatment).

[0268] [Preparation of granular raw material composition] To prepare the granular raw material compositions for the various embodiments and comparative examples, commercially available ZrO2 powder, Y2O3 powder, Nb2O5 powder, Ta2O5 powder, end-capping agent, and TiO2 powder were mixed in the manner described in Tables 1 and 2, with the contents of each component in the sintered zirconia composite sintered body being as specified in Tables 1 and 2. Water was added to prepare a slurry, which was then wet-milled using a ball mill until the average particle size reached below 0.13 μm. After adding a binder to the milled slurry, it was dried using a spray dryer to prepare the granular raw material composition (hereinafter also referred to as the "raw material composition"), which was used to manufacture the molded body described later.

[0269] The aforementioned average particle size refers to the value measured using a laser diffraction / scattering particle size distribution measuring device (Partica LA-950: manufactured by Horiba Corporation), which irradiates a water-diluted slurry with ultrasound for 30 minutes, and then measures the value based on volume while irradiating with ultrasound.

[0270] [Making the Molded Object] Regarding the various embodiments and comparative examples, in order to obtain zirconia composite sintered body samples for evaluating light transmittance and strength as well as for evaluating processability, granular and block-shaped molded bodies were prepared as follows.

[0271] Regarding the granular molded body, a cylindrical mold with a diameter of 19 mm is used, and the aforementioned raw material composition is put into the mold in such a way that the thickness of the sintered zirconia composite is 1.2 mm.

[0272] Next, a uniaxial compression molding machine is used to press the raw material composition with a surface pressure of 200 MPa to produce a granular molded body.

[0273] Furthermore, regarding the block-shaped molded body, with the height of the sintered zirconia composite sintered body being 14.5 mm, the aforementioned raw material composition was filled into a mold with internal dimensions of 19 mm × 18 mm in the order described in Tables 1 and 2. It should be noted that the filling amount of each layer was made equal at this time. Next, a uniaxial pressure molding machine was used to pressurize the raw material composition at a surface pressure of 200 MPa for 90 seconds to produce a layered structure molded body.

[0274] [Preparation of a single-sintered body] For the obtained granular and block-shaped molded bodies, a sintering furnace "NoritakeKatana (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd. was used to hold the samples in the atmosphere at the highest sintering temperatures recorded in Tables 1 and 2 for 2 hours, thereby obtaining granular and block-shaped zirconia composite sintered bodies (one-time sintered bodies).

[0275] [Preparation of HIP-treated sintered bodies] For the obtained granular and blocky zirconia composite sintered bodies (first-time sintered bodies), samples of granular and blocky zirconia composite sintered bodies (HIP-treated sintered bodies) were obtained by using the HIP apparatus "O2-Dr.HIP" manufactured by Kobe Steel Co., Ltd., and holding them in an argon atmosphere at 150 MPa and the HIP temperatures recorded in Tables 1 and 2 for 2 hours.

[0276] Fabrication of Zirconia Composite Sintered Body (Sintered Body After Tempering) For the obtained granular and block-shaped zirconia composite sintered bodies (HIP-treated sintered bodies), a sintering furnace "Noritake Katana (registered trademark) F-1" manufactured by SK Medical Electronics Co., Ltd. was used, and the bodies were held at 700°C for 60 hours to obtain granular and block-shaped zirconia composite sintered body (tempered sintered bodies). Regarding the dimensions of the obtained samples, the granular shape was 15 mm in diameter × 1.2 mm in thickness, and the block shape was 15.7 mm in width × 16.5 mm in length × 14.5 mm in height.

[0277] It should be noted that the content of each component in the zirconia composite sintered body in Tables 1 and 2 is calculated based on the amount of raw materials fed.

[0278] The content (mol%) of the capping elements or ions (e.g., Na) in Tables 1 and 2 is the external addition rate relative to a total of 100 mol% of zirconium oxide, the aforementioned stabilizer (yttrium oxide), Nb2O5 and Ta2O5.

[0279] The percentages (mol%) of zirconium oxide, the aforementioned stabilizer, Nb2O5, and Ta2O5 in Tables 1 and 2 represent the percentages of each component in a total of 100 mol% of zirconium oxide, the aforementioned stabilizer, Nb2O5, and Ta2O5.

[0280] The TiO2 content (mass%) in Tables 1 and 2 is the external addition rate relative to the total mass% of zirconium oxide, the aforementioned stabilizer, Nb2O5 and Ta2O5.

[0281] In Tables 1 and 2, A / B represents the ratio of A to B when the content of Y2O3 is set to A mol%, and the total content of Nb2O5 and Ta2O5 is set to B mol%.

[0282] [Evaluation of the light transmittance of zirconia composite sintered bodies] The light transmittance (n=3) of zirconia composite sintered bodies (tempered sintered bodies) with granular shape directly used in each embodiment and comparative example was evaluated using the following method.

[0283] As the measuring apparatus, the Olympus CrystalEye dental colorimeter (7-band LED light source) was used. First, the background (pad) of the sample was set to white (the side opposite the measuring apparatus relative to the sample was also set to white). The L*a*b* color space (JIS Z 8781-4:2013 Colorimetry—Part 4: CIE 1976 L*a*b* color space) was measured. * Value, set as the first L * value.

[0284] Next, regarding the measurement of the first L * For the same sample after the measurement, set the background (pad) of the sample to black (the side opposite to the measuring device relative to the sample is set to black), and measure the L*a*b* color system. * Value, set as the second L * value.

[0285] In this invention, the first L * Value and the second L * The difference in value (from the first L) * Value minus the second L * The value obtained is set as the light transmittance, expressed as ΔL. * (WB).

[0286] ΔL * A higher (WB) indicates higher light transmittance, while a lower ΔL* indicates lower light transmittance.

[0287] In colorimetry determination, black and white backgrounds (pads) were used with opacity test paper as described in JIS K 5600-4-1:1999 for the relevant determinations of coatings. The ΔL values ​​of each sample were then... * The arithmetic mean of (WB) is shown as the result in Tables 1 and 2.

[0288] [Aesthetic Evaluation of Zirconia Composite Sintered Bodies] The samples with the crown shape of the incisors used in the [Evaluation of the Machinability of Zirconia Composite Sintered Body] described later were observed visually at a very close distance (about 10 cm from the sample) (n=3).

[0289] If all three samples exhibit the same hue (transparency) as natural teeth, the result is rated as "0" (pass).

[0290] If all three samples do not exhibit the same appearance as natural teeth in terms of hue (transparency), they will be evaluated as "×" (unacceptable).

[0291] It should be noted that, in Comparative Example 1, as shown in the results of the processability evaluation in Table 2, the sintered body could not be machined. Therefore, in Comparative Example 1, a pre-fired body obtained by holding a block-shaped molded body at 1000°C for 2 hours was used to process the crown shape of an incisor, and then held at 1550°C for 2 hours to obtain a sample of the crown shape used in the aesthetic evaluation.

[0292] Strength evaluation of zirconia composite sintered bodies The zirconia composite sintered bodies (tempered sintered bodies) in the granular shape of each embodiment and comparative example were used directly. Biaxial bending strength (n=5) was determined using a universal testing machine "AGS-X" (manufactured by Shimadzu Corporation) with the slider speed set to 1.0 mm / min, according to ISO 6872:2015. The arithmetic mean of the test results is shown in Tables 1 and 2. A strength of 300 MPa or higher was considered acceptable.

[0293] [Method for determining the average grain size in sintered bodies] In the granular zirconia composite sintered bodies (tempered sintered bodies) of each embodiment and comparative example, surface images were obtained using a scanning electron microscope (trade name "VE-9800", manufactured by Keyence). After recording the grain boundaries of each crystal grain in the obtained images, the average grain size was calculated by image analysis. The results are shown in Tables 1 and 2 below.

[0294] In the measurement of average grain size, image analysis software (trade name "Image-Pro Plus", manufactured by Pixton Corporation) was used to binarize the read SEM images, adjust the brightness range to make the grain boundaries clear, and identify the grains from the field of view (area). The grain size obtained using Image-Pro Plus refers to the grain size obtained by measuring and averaging the length of the line segment obtained by connecting the outlines of the grains through the centroids obtained from the outlines of the crystalline grains, with the centroid as the center and a 2-degree scale. In the SEM images (3 fields of view) of each embodiment and comparative example, the arithmetic mean of the grain size of all grains excluding the ends of the image is set as the average grain size (number basis) in the sintered body.

[0295] "Excluding grains at the image edges" refers to grains within the SEM image frame that are not fully within the outline (grains whose outlines are truncated at the top, bottom, left, and right boundaries). The full grain size for excluding grains at the image edges can be selected in Image-Pro Plus using the option to remove grains from all boundaries.

[0296] [Evaluation of the processability of zirconia composite sintered bodies] For the blocky zirconia composite sintered bodies (tempered sintered bodies) of each embodiment and comparative example, 30 specimens with metal clamps bonded to a surface 15.7 mm wide × 14.5 mm high were prepared and machined into the crown shape of a typical incisor using the CEREC system "MC-XL" (manufactured by Dentsply Sirona). The machining program used the software "inLab (registered trademark) CAMversion 20.0.1.203841", with IVOCLAR VIVADENT selected as the manufacturer, IPS e.max CAD as the material name, grinding as the production method, C16 as the block size, and Step Bur 12 and Cylinder Pointed Bur 12S as the machining tools.

[0297] [Processing Time] The processing times shown in Tables 1 and 2 refer to the time required from the start of sample processing, using new processing tools and following the conditions described in the above [Evaluation of the Processability of Zirconia Composite Sintered Bodies], to the completion of processing the first sample.

[0298] In addition, if an error occurs due to factors such as the load during processing, the CEREC system "MC-XL" will stop during processing. In this case, new processing tools will be installed, and processing will restart. This process is repeated until one sample is processed, and the required time is set as the processing time.

[0299] It should be noted that in Tables 1 and 2, “×” (impossible) is used to indicate objects that are completely impossible to process.

[0300] [Number of items processed] The number of samples processed as shown in Tables 1 and 2 refers to the number of samples that can be processed into the crown shape of an incisor without changing the processing tools, using a new set of processing tools and the conditions described in the [Evaluation of the Machinability of Zirconia Composite Sintered Body]. The maximum number of samples used in the test is set to 30. If processing can be completed using only one processing tool up to 30 samples, no further processing tests will be conducted; this is always set to "30 or more".

[0301] Furthermore, if an error occurs due to overload or other factors before the first sample is finished, the MC-XL will stop during processing, replace and install new processing tools, and restart processing. This operation is repeated until the processing of one sample is completed, and the reciprocal of the number of processing tools used is taken as the number of samples processed. For example, the statement "0.2 samples" means that using 5 processing tools, one sample processed into the crown shape of an incisor can be obtained. The results are shown in Tables 1 and 2 below.

[0302] [Table 1]

[0303] [Table 2]

[0304] Based on the above results, it can be confirmed that the zirconia composite sintered body of the present invention has strength suitable for dental applications, excellent machinability in the sintered state, and can fully achieve a gradient of light transmittance, resulting in excellent aesthetics.

[0305] In addition, in Examples 1 to 11, the consumption of processing tools can be suppressed, and the number of dental repairs that can be processed continuously using one processing tool is significantly increased.

[0306] On the other hand, in Comparative Example 1, which does not contain Nb2O5 and Ta2O5, it is completely impossible to machine in the sintered state.

[0307] In Comparative Example 2, which does not have a multilayer structure with varying contents of at least one of the stabilizer, Nb2O5, or Ta2O5, the overall structure has high light transmittance. Therefore, the transparency of the portion corresponding to the neck of the tooth is also too high, resulting in poor aesthetics.

[0308] Industrial utilization The zirconia composite sintered body of the present invention possesses strength suitable for dental applications, exhibits excellent machinability and aesthetics in the sintered state. Therefore, the zirconia composite sintered body of the present invention is particularly useful as a dental material, such as dental restorations intended for dental therapeutic purposes.

Claims

1. A zirconia composite sintered body, comprising: zirconium oxide, a stabilizer capable of inhibiting the zirconium oxide phase transformation, and at least one selected from Nb₂O₅ or Ta₂O₅. The zirconia composite sintered body comprises multiple layers having different contents of at least one of the stabilizer, Nb2O5, or Ta2O5 relative to the total molar amount of zirconia, the stabilizer, Nb2O5, and Ta2O5.

2. The zirconia composite sintered body according to claim 1, wherein, The multiple layers are multiple layers with different contents of Nb2O5 or Ta2O5.

3. The zirconia composite sintered body according to claim 2, wherein, Along a straight line extending from one end of the zirconia composite sintered body toward the other, the tendency for the content of Nb2O5 or Ta2O5 to increase or decrease relative to the total molar amounts of zirconia, the stabilizer, Nb2O5, and Ta2O5 does not change from one end to the other.

4. The zirconia composite sintered body according to claim 3, wherein, The stabilizer is yttrium oxide.

5. The zirconia composite sintered body according to claim 4, wherein, Relative to the total moles of zirconium oxide, yttrium oxide, Nb₂O₅, and Ta₂O₅, The layer containing Nb₂O₅ or Ta₂O₅ at one end has a content of 2 mol% or more and 12 mol% or less. The layer containing Nb2O5 or Ta2O5 at the other end has a content of 1 mol% or more and 10 mol% or less.

6. The zirconia composite sintered body according to claim 1, wherein, The multiple layers are multiple layers with different contents of the stabilizer.

7. The zirconia composite sintered body according to claim 6, wherein, Along a straight line extending from one end of the zirconia composite sintered body toward the other, the tendency of the stabilizer content to increase or decrease relative to the total molar amounts of zirconia, the stabilizer, Nb2O5, and Ta2O5 does not change from one end of the zirconia composite sintered body toward the other.

8. The zirconia composite sintered body according to claim 7, wherein, The stabilizer is yttrium oxide.

9. The zirconia composite sintered body according to claim 8, wherein, Relative to the total moles of zirconium oxide, yttrium oxide, Nb₂O₅, and Ta₂O₅, The yttrium oxide content of the layer including one end is more than 1 mol% and less than 8 mol%. The yttrium oxide content of the layer including the other end is 2 mol% or more and 9 mol% or less.

10. The zirconia composite sintered body according to claim 1 or 2, wherein, At least one of the plurality of layers further comprises an element or ion derived from the capping agent.

11. The zirconia composite sintered body according to claim 10, wherein, The content of the element or ion derived from the capping agent is greater than 0 mol% and less than 5 mol% relative to the total 100 mol% of zirconium oxide, the stabilizer, Nb2O5 and Ta2O5.

12. The zirconia composite sintered body according to claim 10, wherein, The element or ion derived from the capping agent is an element or ion belonging to the 2nd to 7th period of the periodic table and whose first ionization energy is smaller than that of a group 18 element in the same period, and / or an element or ion with high electron affinity.

13. The zirconia composite sintered body according to claim 10, wherein, The element or ion derived from the capping agent includes at least one element or its ion selected from Cu, Ag, Li, Na, K, Rb, Cs, Fr, At, I, Br, Cl and F.

14. The zirconia composite sintered body according to claim 10, wherein, The element or ion derived from the capping agent comprises at least one element or its ion selected from Li, Na, K, Rb, Cs, and Fr.

15. The zirconia composite sintered body according to claim 1 or 2, wherein, When the content of the stabilizer is set as A mol%, and the combined content of Nb2O5 and Ta2O5 is set as B mol%, The A / B ratio of at least one of the plurality of layers satisfies a value of 0.9 or higher and 3 or lower.

16. The zirconia composite sintered body according to claim 1 or 2, wherein, At least one of the plurality of layers further comprises a zirconia reinforcing agent, wherein the content of the zirconia reinforcing agent is greater than 0% by mass and less than 6.0% by mass relative to the total mass% of zirconia, the stabilizer, and Nb2O5 and Ta2O5.

17. The zirconia composite sintered body according to claim 16, wherein, The zirconia reinforcing agent comprises TiO2 and / or Al2O3.

18. The zirconia composite sintered body according to claim 1 or 2, wherein, The average grain size of the zirconia composite sintered body is 0.5~5.0 μm.

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