Manufacturing method for ceramic calcined body

Abstract

The present invention provides a method for producing a calcined ceramic body, which can shorten the time until the end of calcination by using a high heating rate and suppress the occurrence of defects.The present invention also relates to a method for producing a calcined ceramic body, which includes a heat treatment step of heating a ceramic molded body, the heat treatment step including a first heat treatment step and a second heat treatment step, and in at least one of the first heat treatment step or the second heat treatment step, the ratio of the heating rate to the oxygen partial pressure (heating rate / oxygen partial pressure) is 7°C / (atm·min) or more and less than 500,000°C / (atm·min), and the molded body contains an organic material.It is preferable that the first heat treatment step is a heat treatment step performed in an atmosphere with an oxygen partial pressure of 0.11 atm or less, and the heating rate in the first heat treatment step is 2.0°C / min or more.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a ceramic calcined body, and more particularly to a method for producing a ceramic calcined body with a high heating rate and suppressing the occurrence of defects such as fractures or cracks. [Background technology]

[0002] Oxide ceramics are widely used industrially. In particular, zirconia sintered bodies have recently been used as dental materials, such as dental prostheses. These dental prostheses are often produced by forming a zirconia molded body having a desired shape, such as a disk or a prism, by pressing zirconia particles or by molding a composition containing zirconia particles, and then calcining this to form a calcined body (mill blank). This is then milled into the shape of the desired dental prosthesis and further sintered.

[0003] A commonly known method for producing a ceramic calcined body is to burn off the organic binder contained in a ceramic compact and then heat the compact to a predetermined temperature.

[0004] The binder removal step (hereinafter also referred to as "debinding step") for removing the organic binder is often carried out by heating the compact in air to a temperature equal to or higher than the temperature at which the organic binder decomposes.

[0005] On the other hand, in order to suppress the occurrence of defects such as cracks and chips that occur during heat treatment of a molded body, a method has been proposed in which the molded body is heated to a predetermined temperature in an inert atmosphere (for example, Patent Document 1). Furthermore, when a calcined body (semi-sintered body) produced by heat-treating a compact at a predetermined temperature under atmospheric conditions is cut and then sintered to produce a sintered body, defects such as cracks and chips occur in the sintered body. Therefore, in order to prevent the occurrence of such defects, a method has been proposed that includes a calcination step in which the sintered body is heated and held in an inert or reducing atmosphere, and then calcined in an active or reducing atmosphere (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 49-074705 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-119485 Summary of the Invention [Problem to be solved by the invention]

[0007] As a result of investigations by the present inventors, Patent Document 1 does not specifically disclose any organic binder other than a Neoprene (registered trademark) (chloroprene rubber)-based binder, nor does it disclose the content thereof, and in addition, the heating rate is only about 1.5°C / min. Furthermore, Patent Document 1 merely discloses that it is extremely difficult to prevent defects such as cracks and chips from occurring during the sintering process in ceramic structures containing organic binders due to their structural characteristics, and does not suggest at all how to shorten the sintering process, since it is extremely difficult even to prevent defects caused by the organic binder. Therefore, Patent Document 1 does not suggest that a high temperature rise rate can be achieved to shorten the time until the end of the calcination (the time from the start of temperature rise to the end of the holding time at the maximum temperature in the calcination process) while suppressing the occurrence of defects such as cracks and chips. Furthermore, Patent Document 2 does not suggest shortening the time.

[0008] In conventional technology, if the heating rate is suddenly increased in order to debinder a molded body containing an organic binder before debinding, defects such as cracks and chips will occur. Therefore, when considering debinding and calcination together, it has been difficult to achieve both a short time until the end of calcination (the time from the start of heating to the end of the holding time at the maximum temperature in the calcination step) using a high heating rate and the prevention of defects such as cracks and chips.

[0009] An object of the present invention is to provide a method for producing a ceramic calcined body, which can shorten the time until the end of calcination by using a high temperature rise rate and can suppress the occurrence of defects. [Means for solving the problem]

[0010] As a result of intensive research into solving the above-mentioned problems, the inventors have found that a ceramic molded body includes a heat treatment step of heating the body, the heat treatment step including a first heat treatment step and a second heat treatment step, and that in at least one of the first heat treatment step or the second heat treatment step, the ratio of the heating rate to the oxygen partial pressure (heating rate / oxygen partial pressure) is 7°C / (atm·min) or more and less than 500,000°C / (atm·min), and that the molded body contains an organic material, thereby making it possible to achieve both a high heating rate and suppression of defect generation. Based on this finding, the inventors have conducted further research and have completed the present invention.

[0011] The present invention includes the following inventions. [1] A heat treatment process for heating a ceramic compact is included, the heat treatment step includes a first heat treatment step and a second heat treatment step, In at least one of the first heat treatment step and the second heat treatment step, the ratio of the temperature rise rate to the oxygen partial pressure (temperature rise rate / oxygen partial pressure) is 7°C / (atm min) or more and less than 500,000°C / (atm min), The method for producing a ceramic calcined body, wherein the compact contains an organic material. [2] The ratio of the temperature rise rate to the oxygen partial pressure in the second heat treatment step (temperature rise rate / oxygen partial pressure) is 7°C / (atm·min) or more and less than 500,000°C / (atm·min), The first heat treatment step is a heat treatment step performed in an atmosphere having an oxygen partial pressure of 0.11 atm or less, The method for producing a ceramic calcined body according to [1], wherein the temperature increase rate in the first heat treatment step is 2.0°C / min or more. [3] The method for producing a ceramic calcined body according to [2], further comprising a calcination step of heating the compact after the first heat treatment step by maintaining a maximum temperature of 800°C or higher and 1300°C or lower in an atmosphere having an oxygen partial pressure of more than 0.12 atm. [4] The second heat treatment step is a step carried out after the first heat treatment step and before the calcination step, The method for producing a ceramic calcined body according to [3], wherein in the second heat treatment step, the compact is heated in an atmosphere having an oxygen partial pressure of more than 0.12 atm. [5] The method for producing a ceramic calcined body according to [4], wherein the temperature increase rate in the second heat treatment step is 2.0°C / min or more. [6] The method for producing a ceramic calcined body according to [4] or [5], wherein the temperature range in the second heat treatment step is 500°C or higher and 1300°C or lower. [7] The method for producing a ceramic calcined body according to [4] or [5], wherein the second heat treatment step further includes a holding step of heating the compact by holding the compact at a constant temperature within a range of 500°C or higher and 1300°C or lower. [8] The method for producing a ceramic calcined body according to any one of [1] to [7], wherein the organic material contains an acrylic acid-based binder. [9] The method for producing a ceramic calcined body according to [8], wherein the content of the organic material is 1 to 12 mass % relative to 100 mass % of the total mass of the ceramic compact.

[10] The molded body is 2.7 cm 3 A rectangular parallelepiped with a volume of more than 19.0 cm and a thickness of more than 1 cm 3 The method for producing a ceramic calcined body according to any one of [1] to [9], wherein the calcined ceramic body is in the form of a disk having a volume of more than 10 ...

[11] The method for producing a ceramic calcined body according to any one of [1] to

[10] , wherein the ceramic contains zirconia and a stabilizer capable of suppressing a phase transition of the zirconia, and the zirconia contains monoclinic zirconia as a main component.

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

[11] , wherein the stabilizer capable of suppressing the phase transition of zirconia is yttria, and the ceramic contains yttria that is not solid-dissolved in zirconia.

[13] The method for producing a ceramic calcined body according to any one of [1] to

[12] , wherein the ceramic further contains TiO2.

[14] The method for producing a ceramic calcined body according to any one of [1] to

[13] , wherein the ceramic further contains Nb2O5.

[15] The method for producing a ceramic calcined body according to any one of [3] to

[14] , wherein the time for the calcination step is within a range of 1 minute to 1 hour.

[16] A method for producing a ceramic calcined body according to any one of [3] to

[15] , wherein the total time from the start of the first heat treatment step to the end of the holding time at the maximum temperature in the calcination step is less than 600 minutes.

[17] The method for producing a ceramic calcined body according to any one of [1] to

[16] , wherein the ceramic calcined body is for producing a dental prosthesis.

[18] A method for producing a ceramic sintered body, comprising a sintering step of sintering the ceramic calcined body obtained by the production method according to any one of [1] to

[17] at a maximum firing temperature of more than 1200°C. [Effects of the Invention]

[0012] According to the present invention, a method for producing a ceramic calcined body can be provided that can shorten the time until the calcination is completed by using a high temperature rise rate, even when the size of the compact is large, and can suppress the occurrence of defects. According to the present invention, the time from the start of temperature increase to the end of calcination can be shortened, so that the manufacturing process can be significantly shortened, which is industrially advantageous. Furthermore, according to the present invention, a method for producing a ceramic calcined body can be provided that can shorten the time until the end of calcination by using a high temperature rise rate and suppress the occurrence of defects, even when the size of the molded body is large. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a graph showing the temperature change and the oxygen concentration change in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] The method for producing a ceramic calcined body of the present invention includes a heat treatment step of heating a ceramic compact, the heat treatment step includes a first heat treatment step and a second heat treatment step, In at least one of the first heat treatment step and the second heat treatment step, the ratio of the temperature rise rate to the oxygen partial pressure (temperature rise rate / oxygen partial pressure) is 7°C / (atm min) or more and less than 500,000°C / (atm min), The molded body includes an organic material.

[0015] In this specification, the term "molded body" refers to a body that has not yet reached a semi-sintered state (calcined state) or a sintered state. In other words, a molded body is distinguished from a calcined body and a sintered body in that the molded body is a body that has been formed by molding and then not yet fired. In this specification, the term "calcined body" refers to a body in a semi-sintered state in which ceramic particles (for example, zirconia particles) are not completely sintered but are necked (adhered) to one another. In this specification, the term "sintered body" refers to a body in a sintered state in which ceramic particles (for example, zirconia particles) are completely sintered. In this specification, the "maximum temperature in the calcination step" means the heating temperature that is finally reached during the calcination step (firing step for obtaining a calcined body) and maintained for a predetermined period of time. In this specification, the "maximum firing temperature" refers to the heating temperature that is finally reached during the sintering step (the firing step for obtaining a sintered body) and maintained for a predetermined period of time. In this specification, the content (mol %) of the stabilizer capable of suppressing the phase transition of zirconia means the content calculated by converting zirconia and the stabilizer into oxides. In this specification, "end of calcination" means that the holding time at the maximum temperature in the calcination step has ended. In this specification, "maintaining" a specific temperature includes changing the temperature within a range that does not deviate from the upper and lower limits of the specific temperature (e.g., from -15°C to +15°C). For example, in calcination at 1000°C, the temperature may change from 985°C to 1015°C by the end of the holding time. In this specification, "zirconia" refers to zirconium (IV) oxide (ZrO), and ZrO particles contain a trace amount of HfO relative to the amount of ZrO (0.5% by mass to 3% by mass). Because HfO is difficult to separate, terms such as "zirconia," "zirconia particles," and "zirconia powder" refer to substances containing ZrO and HfO. Furthermore, particles and powders in which a stabilizer is dissolved in zirconia are also included in the terms "zirconia particles" and "zirconia powder," respectively. In this specification, the "first heat treatment step" refers to the first heating step in which a ceramic compact is heated. In this specification, the "second heat treatment step" refers to a heating step that follows the first heat treatment step over time and is carried out before the calcination step, in which a ceramic molded body is heated, and that differs from the first heat treatment step in at least one atmospheric gas condition (type, pressure, concentration, etc. of atmospheric gas). In this specification, "in the atmosphere" means under standard atmospheric pressure (1 atm). In this specification, the upper and lower limits of the numerical ranges (temperature range, volume, thickness, oxygen partial pressure, oxygen concentration, ratio of heating rate to oxygen partial pressure (heating rate / oxygen partial pressure), content of each component, values ​​calculated from the components, and each physical property, etc.) can be combined as appropriate.

[0016] Furthermore, in at least one of the first heat treatment step or the second heat treatment step, the ratio of the temperature rise rate to the oxygen partial pressure (temperature rise rate / oxygen partial pressure) is 7°C / (atm·min) or more, preferably 15°C / (atm·min) or more, more preferably 100°C / (atm·min) or more, and even more preferably 800°C / (atm·min) or more, from the viewpoints that increasing the temperature rise rate can shorten the time until the completion of calcination and that by combining it with other components (for example, an acrylic acid-based binder, etc.), the occurrence of cracks in the molded body can be more effectively suppressed. Furthermore, the ratio of the heating rate to the oxygen partial pressure (heating rate / oxygen partial pressure) is less than 500,000°C / (atm·min), and is preferably 400,000°C / (atm·min) or less, more preferably 200,000°C / (atm·min) or less, and even more preferably 120,000°C / (atm·min) or less, because increasing the heating rate can shorten the time until the completion of calcination and, by combining it with other components (for example, an acrylic acid-based binder, etc.), can more effectively prevent cracks from occurring in the molded body. In other words, the ratio of the heating rate to the oxygen partial pressure (heating rate / oxygen partial pressure) is preferably 7°C / (atm·min) or more and less than 500,000°C / (atm·min), more preferably 15°C / (atm·min) or more and 400,000°C / (atm·min) or less, even more preferably 100°C / (atm·min) or more and 200,000°C / (atm·min) or less, and particularly preferably 800°C / (atm·min) or more and 120,000°C / (atm·min) or less. In a preferred embodiment, the ratio of the heating rate to the oxygen partial pressure in the second heat treatment step (heating rate / oxygen partial pressure) is preferably less than 50,000°C / (atm·min), more preferably 40,000°C / (atm·min) or less, even more preferably 20,000°C / (atm·min) or less, even more preferably 12,000°C / (atm·min) or less, and particularly preferably 4,000°C / (atm·min) or less, because increasing the heating rate can shorten the time until the completion of calcination and, by combining it with other components (e.g., an acrylic acid-based binder, etc.), can more effectively prevent cracks from occurring in the molded body. The first heat treatment step is a temperature-raising step, which can be rephrased as the first temperature-raising step.

[0017] In one preferred embodiment, the ratio of the heating rate to the oxygen partial pressure (heating rate / oxygen partial pressure) in the first heat treatment step is 7°C / (atm·min) or more and less than 500,000°C / (atm·min), in accordance with the method for producing a ceramic calcined body of the present invention. Another preferred embodiment is the method for producing a ceramic calcined body of the present invention, in which the ratio of the heating rate to the oxygen partial pressure in the second heat treatment step (heating rate / oxygen partial pressure) is 7°C / (atm·min) or more and 4000°C / (atm·min) or less. Another preferred embodiment is the method for producing a ceramic calcined body of the present invention, in which the ratio of the heating rate to the oxygen partial pressure (heating rate / oxygen partial pressure) in the first heat treatment step and the second heat treatment step is 25°C / (atm·min) or more and 120,000°C / (atm·min) or less. The ratio (heating rate / oxygen partial pressure) in the first heat treatment step and the second heat treatment step can be appropriately selected within the ranges described in this specification, and may be the same or different. For example, when the ratio (heating rate / oxygen partial pressure) in both the first heat treatment step and the second heat treatment step is 7°C / (atm·min) or more and less than 500,000°C / (atm·min), the method for producing a ceramic calcined body of the present invention may be such that the ratio (heating rate / oxygen partial pressure) in the first heat treatment step is 15°C / (atm·min) or more and 66,000°C / (atm·min) or less, and the ratio (heating rate / oxygen partial pressure) in the second heat treatment step is 7°C / (atm·min) or more and 20,000°C / (atm·min) or less.

[0018] In this specification, unless otherwise specified, descriptions regarding the rate of temperature rise and the like can be applied to any embodiment as long as the effects of the present invention can be obtained.

[0019] The temperature rise rate in the first heat treatment step is preferably 2.0°C / min or more, more preferably 5.0°C / min or more, even more preferably 10°C / min or more, particularly preferably 15°C / min or more, and most preferably 20°C / min or more. The temperature rise rate in the first heat treatment step is preferably 1000° C. / min or less, more preferably 800° C. / min or less, and even more preferably 500° C. / min or less. In other words, the temperature rise rate in the first heat treatment step is preferably 2.0 to 1000°C / min, more preferably 5.0 to 800°C / min, even more preferably 10 to 500°C / min, particularly preferably 15 to 500°C / min, and most preferably 20 to 500°C / min. The temperature increase rate in the first heat treatment step may be constant or may be varied within the above range. For example, when the temperature increase rate in the first heat treatment step is 5.0°C / min or more, an embodiment is also included in which the temperature increase rate is started at 5.0°C / min and then changed to 50°C / min midway.

[0020] In a preferred embodiment, the ratio of the temperature rise rate to the oxygen partial pressure in the second heat treatment step (temperature rise rate / oxygen partial pressure) is 7°C / (atm min) or more and less than 500,000°C / (atm min), The method for producing a ceramic calcined body may be such that the first heat treatment step is a heat treatment step performed in an atmosphere with an oxygen partial pressure of 0.11 atm or less, and the temperature rise rate in the first heat treatment step is 2.0° C. / min or more.

[0021] In the method for producing a ceramic calcined body of the present invention, the ratio of the heating rate to the oxygen partial pressure (heating rate / oxygen partial pressure) in at least one of the first heat treatment step or the second heat treatment step is equal to or greater than 7°C / (atm·min) and less than 500,000°C / (atm·min), thereby making it possible to increase the heating rate and suppress the occurrence of defects. The reason why the ratio of the heating rate to the oxygen partial pressure (heating rate / oxygen partial pressure) in at least one of the first heat treatment step and the second heat treatment step can be increased by setting the ratio to 7°C / (atm·min) or more and less than 500,000°C / (atm·min) is not clear, but is thought to be as follows. By increasing the heating rate in an atmosphere with a reduced oxygen partial pressure in at least one of the first heat treatment step or the second heat treatment step, when the organic material contained in the molded body is decomposed by heating, carbonization proceeds slowly and little by little over a wide temperature range, and the sudden generation of decomposition gases generated when the organic material decomposes can be suppressed, which is thought to have made it possible to avoid a sudden increase in the amount of decomposition gas generated when a certain temperature is reached, which would cause cracks, etc., in the molded body.

[0022] In the method for producing a ceramic calcined body of the present invention, at least one of the first heat treatment step and the second heat treatment step preferably includes a step of heating the ceramic compact in an atmosphere with an oxygen partial pressure of 0.11 atm or less. Examples of the atmosphere with an oxygen partial pressure of 0.11 atm or less include an inert atmosphere, a reducing atmosphere, a reduced pressure atmosphere, and a vacuum atmosphere.

[0023] The oxygen partial pressure is preferably 0.11 atm or less, more preferably 0.10 atm or less, even more preferably 0.02 atm or less, particularly preferably 0.01 atm or less, and most preferably 0.008 atm or less, because by combining it with other components (for example, an acrylic acid-based binder, etc.), the occurrence of defects can be further suppressed, and the time until the completion of the calcination can be shortened by a high temperature rise rate. The oxygen partial pressure is not particularly limited and may be greater than 0 atm.

[0024] A preferred embodiment of the present invention is a method for producing a ceramic calcined body, in which the oxygen partial pressure in the first heat treatment step is 0.11 atm or less. Another preferred embodiment is the method for producing a ceramic calcined body of the present invention, in which the oxygen partial pressure in the second heat treatment step is 0.11 atm or less. Another preferred embodiment is the method for producing a ceramic calcined body of the present invention, in which the oxygen partial pressure in the first heat treatment step and the second heat treatment step is 0.11 atm or less. The oxygen partial pressures in the first heat treatment step and the second heat treatment step can be appropriately selected within the ranges described in this specification, and may be the same or different. For example, when the oxygen partial pressure in both the first heat treatment step and the second heat treatment step is 0.11 atm or less, the method for producing a ceramic calcined body of the present invention may be such that the oxygen partial pressure in the first heat treatment step is 0.02 atm or less, and the oxygen partial pressure in the second heat treatment step is greater than 0 atm and less than 0.11 atm.

[0025] Examples of inert gases used to create an inert atmosphere include helium gas, neon gas, argon gas, krypton gas, xenon gas, radon gas, nitrogen gas (N2 gas), carbon dioxide gas (CO2 gas), and non-flammable fluorocarbon gas.

[0026] Examples of reducing gases used to create a reducing atmosphere include H gas, hydrogen sulfide gas, ammonia decomposition gas, H diluted with an inert gas (Ar / H), or mixed gases such as carbon monoxide CO and carbon monoxide CO gas diluted with nitrogen N. The reduced pressure atmosphere and vacuum atmosphere can be set using known methods and devices without any particular limitations.

[0027] In addition, the oxygen concentration in the first heat treatment step is preferably 10% or less, more preferably 5% or less, even more preferably 3% or less, particularly preferably less than 1%, and most preferably less than 0.5%, in order to suppress the occurrence of defects when the molded body is large, while also shortening the time until the completion of the calcination by a high heating rate. In a preferred embodiment, the method for producing a ceramic calcined body includes a method in which the oxygen concentration in the first heat treatment step is 0.3% or less. The method for measuring the oxygen concentration is as described in the Examples below.

[0028] The starting temperature in the first heat treatment step is not particularly limited, and may be room temperature or 0°C.

[0029] The temperature reached in the first heat treatment step is preferably 600°C, more preferably 550°C, and even more preferably 500°C.

[0030] The ceramic molded body contains an organic material, such as a methacrylic acid-based binder or an acrylic acid-based binder, with the acrylic acid-based binder being preferred because of its excellent moldability and degreasing speed, and because it can effectively prevent cracks in the molded body caused by gas generation due to violent combustion caused by a sudden temperature rise, when combined with other components.

[0031] The content of organic material contained in the molded body is preferably 12 mass% or less, based on the total mass of the ceramic molded body (100 mass%). In cases where the molded body is large, this suppresses the occurrence of defects while enabling a high heating rate to shorten the time until the completion of calcination. Therefore, it is more preferable that the content be 10 mass%, even more preferable that the content be 8 mass% or less, and particularly preferable that the content be 6 mass% or less. The content of the organic material is preferably 1% by mass or more, more preferably 1.2% by mass or more, even more preferably 1.5% by mass or more, and particularly preferably 2% by mass or more, because this can suppress the occurrence of defects when the molded body is large, while shortening the time until the completion of the calcination by a high heating rate.

[0032] The shape of the molded body is not particularly limited, but examples thereof include a rectangular parallelepiped shape and a disk shape. The size of the molded body is 2.7cm, which is easy to process into a dental prosthesis that corresponds to one natural tooth. 3 A rectangular parallelepiped with a volume of more than 19.0 cm and a thickness of more than 1 cm 3 Preferably, the shape is a disk having a volume of more than 1000 mm and a thickness of more than 1 cm. In the case of a rectangular solid, the volume is 3 cm 3 More preferably, it is 5cm or more. 3 The volume is preferably 125 cm or more, but is not particularly limited thereto. 3 It can be as follows: In the case of a rectangular parallelepiped molded product, the thickness is more preferably 1.2 cm or more, and even more preferably 1.5 cm or more. The thickness is not particularly limited, but can be 5 cm or less. In this specification, the term "disc-shaped" includes not only a circular shape but also a flat shape surrounded by a closed curve, such as an ellipse. In this specification, "rectangular prism" generally refers to a three-dimensional shape composed of six rectangular faces, but also includes cases where each edge and / or vertex is composed of a curved surface, i.e., rounded (for example, those that have been subjected to fillet processing or R processing).

[0033] Examples of ceramics for the molded body include alumina and zirconia, and it is preferable that the molded body contains zirconia as the main component. "Containing zirconia as a main component" means that the zirconia content in the ceramic is 50% by mass or more, preferably 55% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Zirconia may be of any of the monoclinic, tetragonal and cubic crystal systems. In one preferred embodiment, the ceramic contains zirconia and a stabilizer capable of suppressing a phase transition of the zirconia, and the zirconia contains monoclinic zirconia as a main component, in a method for producing a calcined ceramic body. When alumina is used as the ceramic, the molded body does not need to contain a "stabilizer capable of suppressing the phase transition of zirconia" described below.

[0034] "Containing monoclinic zirconia as the main component" means that the proportion of monoclinic zirconia in the ceramic is f m means that the ratio is 50% or more. f m =I 28 / (I 28 +I 30 )×100 (1) (In the formula, f m represents the proportion (%) of monoclinic crystals, and in XRD measurements, I 28 represents the area intensity of the peak near 2θ = 28° where the main peak of the monoclinic system appears, and I 30 represents the integrated intensity of the peak near 2θ=30° where the main peak of the tetragonal or cubic crystal system appears.)

[0035] The proportion of monoclinic zirconia represented by formula (1) is preferably 55% or more, more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more, from the viewpoint of excellent translucency, even when the holding time at the maximum firing temperature is short when producing a sintered body.

[0036] When the ceramic of the molded body contains zirconia as a main component, it is preferable that it further contains a stabilizer capable of suppressing the phase transition of zirconia (hereinafter also simply referred to as "stabilizer").

[0037] Examples of stabilizers capable of suppressing the phase transition of zirconia include calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y2O3), cerium oxide (CeO2), scandium oxide (Sc2O3), niobium oxide (Nb2O5), lanthanum oxide (La2O3), erbium oxide (Er2O3), and praseodymium oxide (Pr2O3, Pr6O 11 Examples of suitable stabilizers include oxides such as samarium oxide (Sm2O3), europium oxide (Eu2O3), thulium oxide (Tm2O3), gallium oxide (Ga2O3), indium oxide (In2O3), and ytterbium oxide (Yb2O3), and from the viewpoints of providing superior effects of the present invention and particularly superior aesthetics, Y2O3 (yttria) and / or CeO2 are preferred. The stabilizers may be used alone or in combination of two or more.

[0038] The content of the stabilizer is preferably 2 mol% or more, more preferably 3 mol% or more, even more preferably 3.5 mol% or more, and particularly preferably 4 mol% or more, based on the total moles of zirconia (zirconium (IV) oxide; ZrO2) and stabilizer. When the content is 2 mol% or more, the crystal structure contained in the sintered body contains more cubic crystals, which is preferable in that the translucency is improved. The content of the stabilizer is preferably 9 mol% or less, more preferably 8.5 mol% or less, even more preferably 8 mol% or less, and particularly preferably 7.5 mol% or less. When it is 9 mol% or less, the proportion of cubic crystals in the encapsulated crystal system is not too high, which is preferable because it is easy to suppress grain growth, the crystal structure does not become too large, and a decrease in translucency is suppressed. The content of the stabilizer may be within any of these ranges. For example, the content of the stabilizer is preferably 2 to 9 mol%, more preferably 3 to 8.5 mol%, even more preferably 3.5 to 8 mol%, and particularly preferably 4 to 7.5 mol%. The content of the stabilizer may be within the range of 3.7 to 8 mol%, as needed.

[0039] The content of the stabilizer in the entire composition can be determined by common analytical methods, such as inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis (XRF), and energy dispersive or wavelength dispersive X-ray analysis associated with a scanning electron microscope (SEM-EDX or SEM-WDX).

[0040] In addition, one preferred embodiment is a method for producing a ceramic calcined body, in which the stabilizer capable of suppressing the phase transition of zirconia is yttria, and the ceramic contains zirconia and yttria that is not solid-dissolved in zirconia. The abundance rate of yttria that is not dissolved in zirconia (hereinafter also referred to as "undissolved yttria") f y can be calculated based on the following formula (2). f y =I 29 / (I 28 +I 29 +I 30 )×100 (2) (In the formula, f y represents the percentage of undissolved yttria (%), and in XRD measurement, I 28 represents the area intensity of the peak near 2θ = 28° where the main peak of the monoclinic system appears, and I 29represents the area intensity of the peak near 2θ = 29° where the main peak of yttria appears, and I 30 represents the integrated intensity of the peak near 2θ=30° where the main peak of the tetragonal or cubic crystal system appears.)

[0041] Undissolved yttria fraction f y From the viewpoint that the desired zirconia sintered body can be easily obtained, the content of undissolved yttria f is preferably greater than 0%, more preferably 1% or more, even more preferably 2% or more, and particularly preferably 3% or more. y The upper limit may be, for example, 25% or less, but preferably depends on the content of yttria in the raw material composition or the compact.

[0042] For example, when the yttria content in the molded body of the present invention or the raw material composition used to produce the molded body (hereinafter simply referred to as "raw material composition") is 3 mol % or more and 8 mol % or less, the following applies. When the yttria content is 3 mol% or more and less than 4.5 mol%, f y When the yttria content is 4.5 mol% or more and less than 5.8 mol%, f y When the yttria content is 5.8 mol% or more and 8 mol% or less, f y can be 25% or less.

[0043] For example, when the yttria content is 3 mol% or more and less than 4.5 mol%, f y is preferably 2% or more, more preferably 3% or more, even more preferably 4% or more, and particularly preferably 5% or more. In other words, when the yttria content is 3 mol% or more and less than 4.5 mol%, f y is preferably 2% or more and 15% or less, more preferably 3% or more and 15% or less, even more preferably 4% or more and 15% or less, and particularly preferably 5% or more and 15% or less. When the yttria content is 4.5 mol% or more and less than 5.8 mol%, f y is preferably 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. In other words, when the yttria content is 4.5 mol% or more and less than 5.8 mol%, f y is preferably 3% or more and 20% or less, more preferably 4% or more and 20% or less, even more preferably 5% or more and 20% or less, even more preferably 6% or more and 20% or less, and particularly preferably 7% or more and 20% or less. When the yttria content is 5.8 mol% or more and 8 mol% or less, f y is preferably 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. In other words, when the yttria content is 5.8 mol% or more and 8 mol% or less, f y is preferably 4% or more and 25% or less, more preferably 5% or more and 25% or less, even more preferably 6% or more and 25% or less, even more preferably 7% or more and 25% or less, and particularly preferably 8% or more and 25% or less.

[0044] In the compact or raw material composition of the present invention, the stabilizer does not necessarily have to be solid-dissolved in ZrO2 and HfO2. In this specification, the phrase "the stabilizer is solid-dissolved" means, for example, that elements (atoms) contained in the stabilizer are solid-dissolved in ZrO2 and HfO2.

[0045] The ceramic compact may further contain Nb2O5 from the viewpoint of machinability. In another preferred embodiment, the ceramic molded body includes zirconia, a stabilizer capable of suppressing a phase transformation of zirconia, Nb2O5 and / or Ta2O5, and an organic material; In a total of 100 mol% of zirconia, the stabilizer, Nb2O5, and Ta2O5, The content of zirconia (total content of ZrO2 and HfO2) is 78 to 97.5 mol%, the content of the stabilizer is 1 to 12 mol %, The total content of Nb2O5 and Ta2O5 is 1 to 9 mol%, Further, there is mentioned a method for producing a ceramic calcined body containing a Group I element. In the above embodiment, the zirconia sintered body obtained by sintering the calcined body (hereinafter referred to as "zirconia composite sintered body") can be machined even in the sintered state, and has excellent machinability.

[0046] The content (mol%) of Group I elements in the compact is the external addition rate relative to the total of 100 mol% of zirconia, the stabilizer, Nb2O5, and Ta2O5. The content of Group I elements is a value calculated by converting the amount (mass) of raw materials charged when added into mol%.

[0047] In the above embodiment, the reason why the zirconia composite sintered body can be machined even in a sintered state is not clear, but is presumed to be as follows. In a zirconia composite sintered body containing zirconia, a stabilizer capable of suppressing the phase transition of zirconia, and Nb2O5 and / or Ta2O5, it is presumed that the presence of a Group I element at the interface between zirconia particles (hereinafter also referred to as "grain boundary") reduces the strength of the grain boundary, thereby acting in a direction that makes it easier for the particles to peel off, making it easier to cut, and improving machinability. Furthermore, since Nb2O5 and / or Ta2O5 act to coarsen the microstructure and reduce hardness in the zirconia composite sintered body, the Group I elements, Nb2O5 and / or Ta2O5 act together to improve machinability. Therefore, the Group I elements, Nb2O5 and / or Ta2O5 act together to provide the strength required for artificial teeth while also imparting excellent machinability.

[0048] Examples of Group I elements include Li, Na, K, Rb, Cs, and Fr. The Group I elements may be used alone or in combination of two or more.

[0049] The content of Group I elements in the molded body is preferably more than 0 mol% and not more than 5.0 mol%, and from the viewpoint of superior machinability, it is more preferably 0.05 mol% to 4.0 mol%, and from the viewpoint of superior strength, it is even more preferably 0.06 mol% to 3.0 mol%, particularly preferably 0.07 mol% to 1.0 mol%, and most preferably 0.08 mol% to 0.34 mol%. The above-mentioned contents can be used as long as it is a Group I element. On the other hand, compared to Li, Na, K, Rb, Cs, and Fr have a higher atomic weight, and as the atomic weight increases, the force acting in the direction that makes it easier for particles to peel from each other increases, and the content required to achieve the effects of the present invention tends to decrease. Therefore, when the Group I element is K, Rb, Cs, or Fr, a lower content range (e.g., 0.05 mol% to 1.0 mol%) can be selected, and when the Group I element is Li and / or Na, a higher content range (e.g., 0.08 mol% to 3.0 mol%) can be selected.

[0050] The zirconia content in the molded body is 78 to 97.5 mol% in a total of 100 mol% of zirconia, the stabilizer, Nb2O5, and Ta2O5, and from the viewpoint of superior translucency and strength, it is preferably 79 mol% or more and 96 mol% or less, more preferably 80 mol% or more and 94 mol% or less, and even more preferably 81 mol% or more and 93 mol% or less.

[0051] The content of the stabilizer in the molded body is preferably 2 mol% or more and 10 mol% or less, based on a total of 100 mol% of zirconia, the stabilizer, Nb2O5, and Ta2O5, and from the viewpoint of achieving better translucency and strength, the content is more preferably 3 mol% or more and 8 mol% or less, and even more preferably 3.5 mol% or more and 7.5 mol% or less.

[0052] When producing a zirconia composite sintered body that is machinable even in a sintered state, the total content of Nb2O5 and Ta2O5 in the compact is 1 to 9 mol%, preferably 1.5 mol% or more and 8.5 mol% or less, based on a total of 100 mol% of zirconia, the stabilizer, Nb2O5, and Ta2O5. In order to act integrally with the Group I elements and achieve better machinability, the total content of Nb2O5 and Ta2O5 is more preferably 2.5 mol% or more and 8 mol% or less, and even more preferably 3 mol% or more and 7 mol% or less. When the total content of Nb2O5 and Ta2O5 is 1 mol% or more, sufficient machinability is easily obtained. Also, when the total content of Nb2O5 and Ta2O5 is 9 mol% or less, the occurrence of chipping and the like is suppressed in the obtained zirconia composite sintered body, and sufficient physical properties are easily obtained.

[0053] The compact for obtaining the zirconia composite sintered body may further contain TiO2. The TiO2 content is preferably more than 0 mass% and 5.0 mass% or less, and more preferably 0.01 mass% or more and 4.5 mass% or less, relative to 100 mass% of the total of zirconia, the stabilizer, Nb2O5, and Ta2O5. Because TiO2 acts as a unit when combined with a Group I element and provides superior strength, the content is even more preferably 0.6 mass% or more and 4.3 mass% or less, particularly preferably 0.7 mass% or more and 3.7 mass% or less, and most preferably 2.5 mass% or more and 3.5 mass% or less.

[0054] The TiO2 content (mass%) is the external addition rate relative to the total of zirconia, the stabilizer, Nb2O5, and Ta2O5 (100 mass%). The TiO2 content can be calculated from the amount (mass) of the raw materials charged when added.

[0055] The zirconia content, stabilizer content, Nb2O5 and Ta2O5 content, Group I element content, and TiO2 content in the compact are the same in the calcined body and the sintered body.

[0056] The molded article of the present invention may contain additives (excluding the stabilizer) such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (Al2O3), titanium oxide (TiO2), silica (SiO2), etc., as needed. These components may be used alone or in combination of two or more. In a preferred embodiment, the method includes a method for producing a ceramic calcined body further containing TiO2. Examples of the pigment include oxides of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Sn, Sb, Bi, Ce, Sm, Eu, Gd, and Er (excluding Y2O3 and CeO2). Examples of the composite pigment include (Zr,V)O2, Fe(Fe,Cr)2O4, (Ni,Co,Fe)(Fe,Cr)2O4·ZrSiO4, and (Co,Zn)Al2O4.

[0057] The molded body of the present invention may contain a fluorescent agent. When the molded body contains a fluorescent agent, the calcined body and the sintered body have fluorescence. The type of fluorescent agent is not particularly limited, and one or more types that can emit fluorescence when exposed to light of any wavelength can be used. Examples of fluorescent agents include those containing metal elements. Examples of such metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one of these metal elements alone, or two or more of them. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred. Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the above metal elements. The fluorescent agents are Y2SiO5:Ce, Y2SiO5:Tb, (Y,Gd,Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, ZnGa2O4:Mn, and BaMgAl. 10 O 17 :Eu, etc.

[0058] The fluorescent agent content in the molded body is not particularly limited and can be adjusted appropriately depending on the type of fluorescent agent or the intended use of the sintered body. However, from the viewpoint of favorable use as a dental prosthesis, the fluorescent agent content is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more, calculated as the oxide of the metal element contained in the fluorescent agent, relative to 100% by mass of zirconia contained in the molded body. Furthermore, the fluorescent agent content is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, calculated as the oxide of the metal element contained in the fluorescent agent. By setting the fluorescent agent content at or above the lower limit, the fluorescence is comparable to that of natural human teeth. By setting the fluorescent agent content at or below the upper limit, the translucency and mechanical strength can be suppressed. In other words, the content of the fluorescent agent is preferably 0.001% by mass to 1% by mass, more preferably 0.005% by mass to 0.5% by mass, and even more preferably 0.01% by mass to 0.1% by mass.

[0059] It is preferable that the method for producing a ceramic calcined body further includes, after the first heat treatment step, a calcination step in which the body is calcined at a maximum temperature (maximum calcination temperature) of 800°C or higher and 1300°C or lower in an atmosphere with an oxygen partial pressure of 0.12 atm or higher.

[0060] The maximum temperature in the calcination step is preferably 800°C or higher, more preferably 850°C or higher, even more preferably 880°C or higher, and particularly preferably 900°C or higher. The maximum temperature in the calcination step is preferably 1300°C or lower, more preferably 1250°C or lower, further preferably 1220°C or lower, and particularly preferably 1200°C or lower. In other words, the maximum temperature in the calcination step is preferably 800°C or higher and 1300°C or lower, more preferably 850°C or higher and 1250°C or lower, even more preferably 880°C or higher and 1220°C or lower, and particularly preferably 900°C or higher and 1200°C or lower.

[0061] The oxygen partial pressure in the calcination step is preferably 0.12 atm or more, more preferably 0.15 atm or more, even more preferably 0.18 atm or more, and particularly preferably 0.20 atm or more.

[0062] The atmospheric conditions in the calcination step are not particularly limited as long as the atmosphere has an oxygen partial pressure of 0.12 atm or more, from the viewpoint of facilitating removal of combustion residues of organic materials, and may be 0.15 atm or more, 0.18 atm or more, or 0.20 atm or more.

[0063] The atmospheric conditions in the calcination step are not particularly limited, and may be atmospheric conditions with an oxygen concentration of about 21% (without vacuum or pressure). The atmospheric conditions may be such that nitrogen gas or the like is flowing in an atmosphere with an oxygen concentration of 12% or more. The oxygen concentration is preferably 15% or more, more preferably 16% or more, even more preferably 18% or more, and particularly preferably 20% or more. The oxygen concentration may be 100% or less, or may be 100%.

[0064] The holding time in the calcination step is not particularly limited as long as the desired ceramic calcined body can be produced, but is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 5 minutes or more. In addition, the duration of the calcination step is preferably 3 hours or less, more preferably 2 hours or less, and even more preferably 1 hour or less, in order to shorten the total time from the start of temperature increase to the end of calcination (the time from the start of temperature increase to the end of the holding time at the maximum temperature in the calcination step).

[0065] The method for producing a ceramic calcined body of the present invention includes a second heat treatment step of heating the compact after the first heat treatment step and before the calcination step. In the second heat treatment step, the compact is preferably heated in an atmosphere with an oxygen partial pressure of 0.12 atm or more, since it is easy to remove combustion residues of organic materials.

[0066] The second heat treatment step preferably includes a temperature-raising step of heating the compact at a temperature-raising rate of 2.0° C. / min or more. The temperature-raising step in the second heat treatment step may be referred to as a second temperature-raising step. The heating rate in the second heating step is preferably 2.0°C / min or more, and is more preferably 5.0°C / min or more, even more preferably 10°C / min or more, particularly preferably 15°C / min or more, and most preferably 20°C / min or more, because a high heating rate can reduce the time until the completion of the calcination while suppressing the occurrence of defects. The temperature increase rate in the second temperature increase step is preferably 1000° C. / min or less, more preferably 800° C. / min or less, and even more preferably 500° C. / min or less. In other words, the temperature rise rate in the second temperature rise step is preferably 2.0 to 1000°C / min, more preferably 5.0 to 800°C / min, even more preferably 10 to 500°C / min, particularly preferably 15 to 500°C / min, and most preferably 20 to 500°C / min. The temperature increase rate in the temperature increase step may be constant or may be varied within the above range. For example, when the temperature increase rate is 5.0°C / min or more in the temperature increase step, an embodiment is also included in which the temperature increase is started at 5.0°C / min and then changed to 50°C / min midway.

[0067] The oxygen partial pressure in the second heat treatment step is preferably 0.12 atm or more, more preferably 0.15 atm or more, even more preferably 0.18 atm or more, and particularly preferably 0.20 atm or more, from the viewpoint of suppressing the occurrence of defects while shortening the time until completion of the calcination by a high temperature rise rate.

[0068] The temperature range in the second heat treatment step is preferably 500°C or higher, more preferably 550°C or higher, even more preferably 580°C or higher, and particularly preferably 600°C or higher. The temperature range in the second heat treatment step is preferably 1300°C or lower, more preferably 1250°C or lower, further preferably 1220°C or lower, and particularly preferably 1200°C or lower. In other words, the temperature range in the second heat treatment step is preferably 500°C or higher and 1300°C or lower, more preferably 550°C or higher and 1250°C or lower, even more preferably 580°C or higher and 1220°C or lower, and particularly preferably 600°C or higher and 1200°C or lower.

[0069] In addition, one preferred embodiment of the method for producing a ceramic calcined body is one in which the second heat treatment step further includes a holding step of heating the molded body by holding the molded body at a constant temperature within a range of 500°C or higher and 1300°C or lower. The second heat treatment process includes a temperature increase process, and in addition to the temperature increase process, a holding process of maintaining the temperature at a constant temperature is also included, which makes it possible to effectively perform degreasing while suppressing the occurrence of defects, and shortens the time until the completion of pre-firing.

[0070] Even in an embodiment of the method for producing a ceramic calcined body of the present invention that does not include the holding step, degreasing is performed during the process of raising the temperature to the maximum temperature (maximum calcination temperature) in the calcination step, so degreasing is not omitted. On the other hand, as in the above-described embodiment, the second heat treatment step may include heating the compact at a predetermined temperature in addition to the heating step. In such an embodiment, debinding can be effectively performed, the high heating rate can shorten the time until the completion of calcination, and the occurrence of defects can be suppressed.

[0071] The temperature in the holding step is not particularly limited as long as it is within the temperature range in the second heat treatment step. In an embodiment including the holding step, the temperature reached in the first heat treatment step may be the holding temperature in the degreasing step. In one embodiment including the holding step, the temperature reached in the first heat treatment step is preferably 200°C or higher, more preferably 300°C or higher, and even more preferably 400°C or higher, in order to ensure sufficient degreasing. In one embodiment including the holding step, the temperature reached in the first heat treatment step is preferably lower than the calcination temperature, and is preferably 650°C or lower, more preferably 620°C or lower, and even more preferably 600°C or lower. In other words, the temperature reached in the first heat treatment step is preferably 200°C or higher and 650°C or lower, more preferably 300°C or higher and 620°C or lower, and even more preferably 400°C or higher and 600°C or lower.

[0072] In the embodiment having the holding step, the second heat treatment step may have a holding step of holding the temperature reached in the first heat treatment step (500°C or higher) followed by a heating step, as long as the effects of the present invention are achieved, or may have a heating step after the first heat treatment step, followed by a holding step of holding the molded body at a predetermined temperature, and further have a heating step.

[0073] In the method for producing a ceramic calcined body of the present invention, the total time from the start of the first heat treatment step to the end of the holding time at the maximum temperature in the calcination step is preferably less than 600 minutes, more preferably 300 minutes or less, even more preferably 200 minutes or less, and particularly preferably 100 minutes or less.

[0074] In the method for producing a ceramic calcined body of the present invention, the conditions for lowering the temperature after the holding time at the maximum temperature in the calcination step (after the end of calcination) are not particularly limited, but can be the same atmospheric conditions as in the calcination step. The rate of temperature reduction during cooling is not particularly limited, and is preferably 2.0°C / min or more, more preferably 5.0°C / min or more, even more preferably 10°C / min or more, particularly preferably 15°C / min or more, and most preferably 20°C / min or more. This can vary depending on the embodiment, and the temperature drop rate may be 100° C. / min or more.

[0075] There are no particular limitations on the method for producing the ceramic compact used in the ceramic calcined body of the present invention. For example, when the ceramic contains zirconia and a stabilizer (for example, yttria), it can be produced by the following method.

[0076] A raw material composition containing zirconia powder and stabilizer powder is prepared, and the raw material composition is press-molded at a predetermined pressure to obtain a zirconia molded body.

[0077] The raw material composition is prepared by mixing zirconia powder (e.g., zirconia powder containing monoclinic zirconia as a main component) and stabilizer powder (e.g., yttria powder) to obtain a desired stabilizer content.

[0078] There are no particular limitations on the method for producing the zirconia powder, and known methods such as a breakdown process in which coarse particles are pulverized into fine powder, or a building-up process in which zirconia is synthesized from atoms or ions through a nucleation and growth process can be used.

[0079] Moreover, commercially available zirconia powder can be used as the zirconia powder. The stabilizer powder (for example, yttria powder) may be, for example, a commercially available product, or the commercially available powder may be used after being pulverized in a known pulverizing / mixing device (such as a ball mill).

[0080] Commercially available zirconia powders include, for example, "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%). Examples 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%); all manufactured by Tosoh Corporation. The commercially available zirconia powder also contains HfO2. Commercially available zirconia powders containing Y2O3 in addition to zirconia can also be used. As the zirconia powder, zirconia powder in which Y2O3 is uniformly dispersed and solid-solved, such as the commercially available TZ series (part of the product name includes "TZ"), can also be used. The zirconia powder may be used alone or in combination of two or more types, taking into consideration the crystal system, the content of the stabilizer, and the like.

[0081] A mixture of zirconia powder and stabilizer powder is added to water to prepare a slurry, which is then pulverized (for example, wet pulverized) in a pulverizer until the desired particle size is reached, and then mixed. The pulverized slurry is dried and granulated, and the resulting powder is then fired at a temperature (for example, 800 to 1200°C) that does not result in sintering of the zirconia particles to produce a primary powder. The pulverizer used for pulverization is not particularly limited, and any known pulverizer can be used, for example, a ball mill, etc. The method for drying the slurry after pulverization is not particularly limited, but spray drying is preferred. There are no particular limitations on the spray drying, and any known spray dryer can be used. The average particle size of the primary powder is not particularly limited, but is preferably, for example, 0.2 μm or less in terms of the light transmittance of the resulting sintered body. The average particle size can be determined by a laser diffraction scattering method, specifically, for example, by a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation) using a 0.2% aqueous solution of sodium hexametaphosphate as a dispersion medium and measuring on a volume basis.

[0082] The primary powder obtained as described above is added to water to prepare a slurry, which is then pulverized (for example, wet pulverized) in a pulverizer to a desired particle size and mixed. After the pulverization, an organic material (preferably an acrylic acid-based binder) and, if necessary, optional components such as a pigment and a fluorescent agent are added to the slurry, which is then dried to produce a secondary powder. The organic material is usually added after pulverization, but it may be added during or before the pulverization process of the slurry in the pulverizer. The pulverizer and drying method used for pulverization can be the same as those used for producing the primary powder. The average particle size of the secondary powder is not particularly limited, but is preferably, for example, 0.2 μm or less in terms of the light transmittance of the resulting sintered body.

[0083] The secondary powder obtained as described above is used as a raw material composition. If optional components such as pigments and fluorescent agents are not added during the production of the secondary powder, the optional components may be added to the obtained secondary powder. The type and content of the ceramics (including the proportion of zirconia crystals), the type and content of the stabilizer, the type and content of the organic material, etc. in the raw material composition are the same as those in the molded body. Regarding the content of the organic material, "based on 100% by mass of the total mass of the ceramic molded body" can be read as "based on 100% by mass of the total mass of the raw material composition."

[0084] Next, the obtained raw material composition is molded to produce a molded body. The molding method is not particularly limited, and known methods (for example, press molding) can be used.

[0085] When a zirconia molded body is produced by a method including a step of press-molding a raw material composition, the specific press-molding method is not particularly limited, and the press-molding can be carried out using a known press-molding machine. Specific examples of the press-molding method include a method in which the raw material composition is filled into a predetermined mold and uniaxially pressed.

[0086] The optimum pressure is set depending on the size, hardness, biaxial bending strength, particle size of the raw material powder, etc. of the desired compact, and is usually 5 MPa or more and 1000 MPa or less. Increasing the pressing pressure during molding in the above-described manufacturing method allows the pores of the resulting molded body to be more fully filled, thereby increasing the density of the molded body. In addition, in order to increase the density of the resulting zirconia molded body, a cold isostatic pressing (CIP) treatment may be further performed after uniaxial pressing.

[0087] The firing furnace used in the method for producing a ceramic calcined body of the present invention is not particularly limited, and may be a firing furnace of either a batch type or a continuous type operation type. Examples of the batch-type firing furnace include a batch-type electric furnace. An example of a continuous firing furnace is a RHK (Roller Hearth Kiln).

[0088] In the method for producing a ceramic calcined body according to the present invention, other optional conditions may be included, such as performing the second heat treatment step and the calcination step in the presence of superheated steam when removing the organic binder. It is also conceivable that rapid decomposition of the organic binder can be suppressed by applying heated steam to the compact at a temperature that is about 1 to 10°C different from the temperature at which the organic binder begins to decompose. On the other hand, by not including a step such as applying superheated steam to the surface of the molded body, the desired ceramic calcined body can be produced more easily, and the high heating rate can also shorten the time until the end of the calcination (the time from the start of heating to the end of the holding time at the maximum temperature in the calcination process).

[0089] In the method for producing a ceramic calcined body according to the present invention, organic components are eliminated in the calcination step and / or the second heat treatment step, so the ceramic calcined body does not contain carbon, and the carbon content in the ceramic calcined body is less than 0.01 mass%. The carbon content in the ceramic calcined body is measured by measuring the mass of the ceramic calcined body before heat treatment in air (mass before treatment), and measuring the mass of the ceramic calcined body after heat treatment in air (mass after treatment), and the difference between the masses is taken as the carbon content in the ceramic calcined body. The heat treatment temperature in the method for measuring the carbon content is not particularly limited as long as it is a temperature at which the organic material is burned away, but it can be set to 700°C, for example.

[0090] The ceramic calcined body obtained by the production method of the present invention may have a predetermined shape. Furthermore, for example, the ceramic calcined body can have a disk shape, a rectangular parallelepiped shape, or a dental product shape (for example, a dental crown shape). The type and content of the ceramic (including the proportion of zirconia crystal system) and the type and content of the stabilizer in the ceramic calcined body of the present invention are the same as those in the molded body.

[0091] The physical properties of the ceramic calcined body will be explained below by taking as an example a zirconia calcined body when the ceramic contains zirconia. In the following, the term "zirconia calcined body" can be read as "ceramic calcined body" or "alumina calcined body."

[0092] The bending strength (three-point bending strength) of the calcined zirconia body is preferably 15 MPa or more to ensure strength that allows machining, and the bending strength of the calcined body is preferably 70 MPa or less, more preferably 60 MPa or less, to facilitate machining.

[0093] The bending strength can be measured in accordance with ISO 6872:2015 (Dentistry - Ceramic materials), except for the size of the test specimen, which is 5 mm x 10 mm x 50 mm. The test specimen's face and C-face (the surface where the corner of the test specimen is chamfered at a 45° angle) are sanded longitudinally with 600-grit sandpaper. The test specimen is positioned so that the widest surface faces vertically (the load direction). In the bending test, the span is 30 mm and the crosshead speed is 0.5 mm / min. The bending strength of the zirconia calcined body can be adjusted by the pressing pressure when producing the compact, the content of the organic material (preferably an acrylic acid-based binder), the maximum temperature in the calcination step, the holding time at the maximum temperature, etc.

[0094] From the viewpoint of polishability, the Vickers hardness of the zirconia calcined body is preferably 350 HV 1 / 15 or less, more preferably 300 HV 1 / 15 or less, and even more preferably 100 HV 1 / 15 or less. When the Vickers hardness is 350HV 1 / 15 or less, the machinability (cutting and grinding properties) is excellent, and the rate of chipping can be reduced. "HV 1 / 15" means the Vickers hardness when a load (test force) of 1 kgf is held for 15 seconds.

[0095] The method for measuring the Vickers hardness of the zirconia calcined body according to the present invention conforms to JIS Z 2244:2020. The Vickers hardness of the zirconia calcined body can be adjusted by the proportion of a stabilizer (e.g., yttria) that is not dissolved in zirconia in the calcined body, the density of the calcined body, the average particle size of the particles contained in the calcined body, the bending strength of the calcined body, etc.

[0096] The density of the zirconia calcined body according to the present invention is 2.7 to 4.0 g / cm3 in view of excellent machinability. 3 It is preferable that the density is 2.9 to 3.6 g / cm 3 More preferably, it is 3.1 to 3.4 g / cm 3 It is more preferable that:

[0097] The density of the zirconia calcined body means the bulk density. The density of the zirconia calcined body can be calculated, for example, by dividing the mass of the calcined body by the volume of the calcined body. Specifically, the dimensions of the test piece are accurately measured using a micrometer, and the mass of the calcined body is measured using a precision balance, and the density can be calculated by dividing the mass of the calcined body by the volume of the calcined body (average value of n=3). The density of the zirconia calcined body can be adjusted by the average particle size of the particles contained in the calcined body, the content of the binder, and the like.

[0098] The ceramic calcined body (e.g., zirconia calcined body) obtained by the method for producing a ceramic calcined body according to the present invention has a white-based color tone, excellent translucency, and excellent aesthetic properties, and therefore can be suitably used for producing dental prostheses.

[0099] Another embodiment is a method for producing a ceramic sintered body, which includes a sintering step of sintering a ceramic calcined body obtained by any of the above-mentioned production methods at a maximum firing temperature of more than 1200°C.

[0100] The ceramic calcined body used in the method for producing a ceramic sintered body is preferably subjected to a processing step before the sintering step, in which, for example, a disk-shaped ceramic calcined body is machined using a CAD / CAM (Computer-Aided Design / Computer-Aided Manufacturing) system to have the shape of a dental product (e.g., a dental prosthesis in the shape of a tooth crown).

[0101] The atmospheric conditions in the sintering step are the same as those in the calcination step.

[0102] The maximum firing temperature is preferably above 1300°C, more preferably at least 1350°C, and even more preferably at least 1400°C. The maximum firing temperature is preferably at most 1650°C, more preferably at most 1600°C, and even more preferably at most 1580°C.

[0103] In the sintering step, there is no particular limitation on the sintering time (holding time). However, in order to obtain the desired zirconia sintered body efficiently and stably with good productivity, the sintering time is preferably 5 minutes or more, more preferably 15 minutes or more, and even more preferably 30 minutes or more, and is preferably 6 hours or less, more preferably 4 hours or less, and even more preferably 2 hours or less.

[0104] According to the zirconia calcined body of the present invention, by adjusting the content of monoclinic crystals (for example, by using monoclinic zirconia powder as a raw material) or by adjusting the proportion of undissolved yttria (for example, by increasing the blending ratio of yttria powder), it is possible to suppress a decrease in the translucency of the produced zirconia sintered body even when the holding time at the maximum firing temperature is short. Furthermore, by shortening the firing time, it is possible to increase production efficiency and reduce energy costs.

[0105] The temperature increase and decrease rates in the sintering step are preferably set so as to shorten the time required for the sintering step. For example, the temperature increase rate can be set so as to reach the maximum firing temperature in the shortest time possible, depending on the performance of the firing furnace. The temperature increase rate up to the maximum firing temperature can be, for example, 10°C / min or more, 50°C / min or more, 100°C / min or more, 120°C / min or more, 150°C / min or more, or 200°C / min or more. The temperature decrease rate is preferably set so as not to cause defects such as cracks in the sintered body. For example, after heating is completed, the sintered body can be allowed to cool at room temperature.

[0106] The zirconia sintered body obtained by firing the zirconia calcined body of the present invention can be suitably used for dental products. Examples of dental products include copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, orthodontic wires, and laminate veneers. By using the zirconia calcined body of the present invention for parts such as implant screws and implant fixtures, discoloration of the gums that would occur if metal materials were used can be suppressed, resulting in excellent aesthetics. The manufacturing method can be selected appropriately depending on the application, but for example, dental products can be obtained by cutting the zirconia calcined body of the present invention and then sintering it. It is preferable to use a CAD / CAM system for the cutting process.

[0107] The relative density of the zirconia sintered body is preferably 99.5% or more. The relative density can be calculated as the ratio of the actual density measured by Archimedes' method to the theoretical density.

[0108] The present invention includes embodiments in which all or part of the above-described configurations are combined in various ways within the scope of the technical concept of the present invention, as long as the effects of the present invention are achieved. [Example]

[0109] Next, the present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way, and many modifications within the technical scope of the present invention are possible by those skilled in the art.

[0110] [Preparation of raw material composition] The method for producing the raw material compositions used to produce the zirconia molded bodies of Examples 1 to 14 and 16 to 20 will be described using Example 1 as an example. First, a mixture was prepared using approximately 100% monoclinic zirconia powder and yttria powder, with the yttria content relative to the total moles of zirconia and yttria being the content shown in Table 1. Next, this mixture was added to water to prepare a slurry, which was then wet-pulverized and mixed in a ball mill until the average particle size was 0.13 μm or less. A binder (acrylic acid-based binder) was added to the pulverized slurry so that the content shown in Table 1 was achieved relative to 100% by mass of the total mass of the raw material composition, and the mixture was then dried in a spray dryer to prepare granules (secondary powder). The prepared granules were used as the raw material composition to manufacture the zirconia molded body described below. The average particle size can be determined by a laser diffraction scattering method, specifically, for example, by a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation) using a 0.2% aqueous solution of sodium hexametaphosphate as a dispersion medium and measuring on a volume basis.

[0111] The obtained primary powder was added to water to prepare a slurry, which was then wet-pulverized and mixed in a ball mill until the average particle size reached 0.13 μm or less. A binder (acrylic acid-based binder) was added to the pulverized slurry in an amount shown in Table 1, based on 100% by mass of the total mass of the raw material composition, and the mixture was then dried in a spray dryer to prepare granules (secondary powder). The prepared granules were used as the raw material composition to manufacture the zirconia molded body described below.

[0112] In Example 15 and Comparative Example 1, instead of monoclinic zirconia powder, "Zpex (registered trademark) Smile (registered trademark)" (Y2O3 content: 5.5 mol%) (manufactured by Tosoh Corporation), a raw material in which yttria is solid-dissolved in zirconia, was used. In Comparative Example 2, instead of the monoclinic zirconia powder, "TZ-3YS-E" (Y2O3 content: 3 mol%) (manufactured by Tosoh Corporation), a raw material in which yttria is solid-dissolved in zirconia, was used.

[0113] [Table 1]

[0114] In Table 1, the content of each component is as follows: The NaOH content (mol%) and the Al2O3 content (mol%) are externally added rates relative to the total of zirconia, Y2O3, and Nb2O5, which is 100 mol%. In Table 1, the TiO2 content (mass %) and the colorant content (mass %) are externally added rates relative to the total of zirconia, Y2O3, and Nb2O5, which is 100 mass %. In Table 1, the content (mol %) of Nb2O5 is the content in a total of 100 mol % of zirconia, Y2O3, and Nb2O5. The Y2O3 content (mol %) is the content in a total of 100 mol % of zirconia, Y2O3, Al2O3, and Nb2O5.

[0115] [Preparation of zirconia compact] For each of the Examples and Comparative Examples, a rectangular parallelepiped compact was prepared as follows so as to obtain a calcined sample for evaluation of breakage and crack occurrence and for evaluation of internal residual carbon. To prepare a rectangular shaped compact, for each of the Examples and Comparative Examples, a rectangular shaped mold having dimensions of 19 mm length x 20 mm width was used, and the granules of the raw material composition were placed in the mold so that the thickness of the zirconia compact after molding would be 21 mm. Next, the raw material composition was press-molded at a surface pressure of 200 MPa using a uniaxial press molding machine to obtain a rectangular parallelepiped zirconia molded body.

[0116] [Example 1] The zirconia molded body obtained as described above was heated to 600° C. in a test electric furnace under the atmospheric conditions and at the heating rate shown in Table 2. Next, a holding step of the second heat treatment step was carried out at 600°C under the atmospheric conditions and holding time shown in Table 2. After the holding step, the temperature was further increased to 1000°C at the temperature increase rate and under the atmospheric conditions of the second heat treatment step shown in Table 2. Further, calcination was carried out at a maximum temperature of 1000° C. under the atmospheric conditions and for the holding time shown in Table 3 to produce a zirconia calcined body. FIG. 1 shows the change in oxygen concentration 1 (%) (scale: right side) and the change in temperature 2 (° C.) in Example 1.

[0117] [Examples 2 to 20 and Comparative Examples 1 and 2] A zirconia calcined body was produced in the same manner as in Example 1, except that the conditions for the first heat treatment step, the second heat treatment step, and the calcination step were changed to those shown in Tables 2 and 3. In Examples 6 to 15, the calcination and degreasing were carried out simultaneously.

[0118] [Measurement of oxygen concentration and oxygen partial pressure] An oxygen sensor (zirconia type O2 sensor, product name "TB-II FR", manufactured by Daiichi Nekken Co., Ltd.) was installed in the test electric furnace to measure the oxygen concentration and oxygen partial pressure.

[0119] [Evaluation of cracking and crack occurrence in zirconia calcined body] Ten zirconia calcined bodies were produced for each example or comparative example, and the presence or absence of breakage and cracks on the surface of these zirconia calcined bodies was visually evaluated. If even one crack or break was found on the surface, it was rated as "present," and if no crack or break was found on the surface, it was rated as "absent." The results are shown in Table 4.

[0120] [Evaluation of residual carbon inside zirconia calcined body] The calcined zirconia body was cut along a plane passing through the center, and visually inspected to determine whether black to gray residual carbon was present in the center, and evaluated as "present" if no residual carbon was present. The results are shown in Table 4.

[0121] [Evaluation of pass / fail for zirconia calcined body] The samples that were rated as "None" in the [Evaluation of cracking and crack occurrence in zirconia calcined body] and "None" in the [Evaluation of residual carbon inside zirconia calcined body], and the total time from the start of the first heat treatment step to the end of the holding time at the maximum temperature in the calcination step was less than 800 minutes, were rated as "Pass", and the rest were rated as "Fail".

[0122] [Table 2]

[0123] [Table 3] Tables 2 and 3 show consecutive steps, which were carried out in the order of Tables 2 to 3. In Tables 2 and 3, the meanings of each notation are as follows: "RHK" means continuous kiln. "N2 flow" means that the inside of the test electric furnace is almost entirely replaced with N2. "Air + N2 flow" means that the flow rate of N2 is low and it is mixed with air. "N2+wet flow" means "N2 flow" containing water vapor. "Decompression" means that the pressure was reduced to about 2 kPa using a vacuum pump in an automatic vacuum / gas replacement electric furnace (product name "VF-5000", manufactured by SK Medical Electronics Co., Ltd.).

[0124] [Table 4]

[0125] From the above results, it was confirmed that the method for producing a ceramic calcined body of the present invention can shorten the time until the end of calcination and can suppress the occurrence of defects. [Industrial Applicability]

[0126] The method for producing a ceramic calcined body of the present invention is industrially advantageous because it can greatly shorten the production steps and significantly reduce production costs. [Explanation of symbols]

[0127] 1. Oxygen concentration 2 Temperature

Claims

1. A heat treatment step of heating the ceramic compact is included, the heat treatment step includes a first heat treatment step and a second heat treatment step, After the first heat treatment step, the method further includes a calcination step of heating the molded body at a maximum temperature of 800°C or higher and 1300°C or lower in an atmosphere having an oxygen partial pressure of more than 0.12 atm, the first heat treatment step is a heat treatment step performed in an atmosphere having an oxygen partial pressure of 0.11 atm or less, the temperature rising rate in the first heat treatment step is 2.0°C / min or more; In the second heat treatment step, the ratio of the temperature rise rate to the oxygen partial pressure (temperature rise rate / oxygen partial pressure) is 7° C. / (atm min) or more and less than 500,000° C. / (atm min), The second heat treatment step is a step carried out after the first heat treatment step and before the calcination step, In the second heat treatment step, the compact is heated in an atmosphere having an oxygen partial pressure of more than 0.12 atm, The method for producing a ceramic calcined body, wherein the compact contains an organic material.

2. 2. The method for producing a ceramic calcined body according to claim 1, wherein the temperature increase rate in the second heat treatment step is 2.0°C / min or more.

3. The method for producing a ceramic calcined body according to claim 1 or 2, wherein the temperature range in the second heat treatment step is 500°C or higher and 1300°C or lower.

4. 3. The method for producing a ceramic calcined body according to claim 1, wherein the second heat treatment step further includes a holding step of heating the compact by holding the compact at a constant temperature within a range of 500°C or higher and 1300°C or lower.

5. The method for producing a ceramic calcined body according to claim 1 , wherein the organic material includes an acrylic acid-based binder.

6. The method for producing a ceramic calcined body according to claim 5, wherein the content of the organic material is 1 to 12 mass% with respect to 100 mass% of the total mass of the ceramic compact.

7. The molded body is 2.7 cm 3 a rectangular parallelepiped having a volume of more than 19.0 cm and a thickness of more than 1 cm; 3 2. The method for producing a ceramic calcined body according to claim 1, wherein the calcined body is in the form of a disk having a volume of more than 10000000000 and a thickness of 1 cm or more.

8. 2. The method for producing a ceramic calcined body according to claim 1, wherein the ceramic contains zirconia and a stabilizer capable of suppressing a phase transition of the zirconia, and the zirconia contains monoclinic zirconia as a main component.

9. 9. The method for producing a ceramic calcined body according to claim 8, wherein the stabilizer capable of suppressing the phase transition of zirconia is yttria, and the ceramic contains yttria that is not solid-dissolved in zirconia.

10. The ceramics may be TiO 2 The method for producing a ceramic calcined body according to claim 1, further comprising:

11. The ceramics is Nb 2 O 5 The method for producing a ceramic calcined body according to claim 1, further comprising:

12. The method for producing a ceramic calcined body according to claim 1, wherein the time for the calcination step is within a range of 1 minute to 1 hour.

13. 13. The method for producing a ceramic calcined body according to claim 1 or 12, wherein a total time from the start of the first heat treatment step to the end of a holding time at the maximum temperature in the calcination step is less than 600 minutes.

14. The method for producing a ceramic calcined body according to claim 1, wherein the ceramic calcined body is used to produce a dental prosthesis.

15. A method for producing a ceramic sintered body, comprising a sintering step of sintering the ceramic calcined body obtained by the method of claim 1 at a maximum firing temperature of more than 1200°C.

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