Method for producing ceramic calcined body

Abstract

The present invention provides a method for producing a ceramic calcined body with which it is possible to shorten the time until the end of calcination by a high heating rate and suppress the occurrence of defects. The present invention pertains to a method for producing a ceramic calcined body, the method including a heat treatment step for heating a ceramic molded body. 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 (heating rate / oxygen partial pressure) of the heating rate to the oxygen partial pressure is from 7°C / (atm∙min) to less than 500,000° C / (atm∙min), and the molded body contains an organic material. The first heat treatment step is a heat treatment step in an atmosphere having an oxygen partial pressure of 0.11 atm or less, and the heating rate in the first heat treatment step is preferably 2.0°C / min or more.

Description

Manufacturing method for ceramic calcined body

[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.

[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 press-molding zirconia particles or by molding a composition containing zirconia particles, followed by calcining the zirconia molded body to obtain a calcined body (mill blank), which is then milled into the shape of the desired dental prosthesis and then 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] Meanwhile, in order to suppress the occurrence of defects such as cracks and chips that occur during heat treatment of a molded body, a method of heating to a predetermined temperature in an inert atmosphere has been proposed (for example, Patent Document 1). Also, when a calcined body (semi-sintered body) produced by heat treating a molded body 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 suppress the occurrence of such defects, a method has been proposed that includes a calcination step of heating and holding the body in an inert or reducing atmosphere, and then calcining in an active or reducing atmosphere (Patent Document 2).

[0006] JP 49-074705 A JP 2013-119485 A

[0007] The inventors' investigations revealed that 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 of the binder. Furthermore, the heating rate is only approximately 1.5°C / min. Furthermore, Patent Document 1 merely discloses that, due to the structural characteristics of ceramic structures containing organic binders, it is extremely difficult to prevent defects such as cracks and chips during the sintering process. Since even preventing defects due to the organic binder is extremely difficult, Patent Document 1 does not suggest shortening the sintering process. Therefore, Patent Document 1 does not suggest achieving both a high heating rate to shorten the time from 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 process) and to prevent defects such as cracks and chips. Patent Document 2 also does not suggest shortening the sintering process.

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

[0010] As a result of intensive research into solving the above problems, the inventors have discovered 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 method for producing a calcined ceramic body, comprising a heat treatment step of heating a ceramic molded body, the heat treatment step comprising a first heat treatment step and a second heat treatment step, wherein 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 and less than 500,000°C / (atm min), and the molded body contains an organic material. [2] A method for producing a calcined ceramic body according to [1], wherein the ratio of the temperature rise rate to the oxygen partial pressure (temperature rise rate / oxygen partial pressure) in the second heat treatment step is 7°C / (atm min) or more and less than 500,000°C / (atm min), and 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. [3] The method for producing a ceramic calcined body according to [2], further comprising, after the first heat treatment step, a calcination step of heating the shaped body while 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 method for producing a ceramic calcined body according to [3], wherein the second heat treatment step is a step carried out after the first heat treatment step and before the calcination step, and the shaped body 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 rise rate in the second heat treatment step is 2.0°C / min or higher. [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 comprises a holding step of heating the compact by holding the compact at a constant temperature in the 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 comprises an acrylic acid 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 method for producing a ceramic calcined body according to [8], wherein the compact has a diameter of 2.7 cm 3a rectangular parallelepiped having a volume of more than 19.0 cm and a thickness of more than 1 cm; 3

[10] A method for producing a calcined ceramic body according to any one of [1] to [9], wherein the calcined ceramic body has a volume of more than 10 ...

[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 calcining step is less than 600 minutes.

[17] A 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.

[0012] According to the present invention, it is possible to provide a method for producing a ceramic calcined body that can shorten the time until the end of calcination by using a high heating rate and suppress the occurrence of defects, even when the size of the molded body is large. According to the present invention, it is possible to shorten the time from the start of heating to the end of calcination, which significantly shortens the production process and is industrially advantageous. Furthermore, according to the present invention, it is possible to provide a method for producing a ceramic calcined body that can shorten the time until the end of calcination by using a high heating rate and suppress the occurrence of defects, even when the size of the molded body is large.

[0013] 1 is a graph showing a change in temperature and a change in oxygen concentration in Example 1.

[0014] The method for producing a ceramic calcined body of the present invention 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.

[0015] As used herein, the term "molded body" refers to a body that has not yet reached either a semi-sintered state (calcined state) or a sintered state. In other words, a molded body is distinguished from a calcined body and a sintered body in that it is a body that has not yet been fired after being formed into a molded body by molding. As used herein, a "calcined body" refers to a body in a semi-sintered state in which ceramic particles (e.g., zirconia particles) are necked (adhered) to each other and the ceramic particles are not completely sintered. As used herein, a "sintered body" refers to a body in a sintered state in which the ceramic particles (e.g., zirconia particles) are completely sintered. As used herein, the term "maximum temperature in the calcination process" refers to the heating temperature finally reached during the calcination process (the firing process for obtaining a calcined body) and maintained for a predetermined period of time. As used herein, the term "maximum firing temperature" refers to the heating temperature finally reached during the sintering process (the firing process for obtaining a sintered body) and maintained for a predetermined period of time. As used herein, the content (mol %) of a stabilizer capable of suppressing the phase transition of zirconia refers to the content of zirconia and the stabilizer calculated in terms of oxide. In this specification, "end of calcination" refers to the end of the holding time at the highest temperature in the calcination step. In this specification, "maintaining" a specific temperature also includes changing the temperature within a range that does not deviate from the upper or lower limit of the specific temperature (e.g., -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 (0.5% by mass to 3% by mass) relative to the amount of ZrO. Because HfO is difficult to separate, terms such as "zirconia," "zirconia particles," and "zirconia powder" refer to substances that contain both ZrO and HfO. Furthermore, particles and powders in which a stabilizer is solid-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 (e.g., type, pressure, concentration, etc.) from the first heat treatment step. In this specification, "in the atmosphere" refers to a condition 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 appropriately combined.

[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 the 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 temperature rise rate to the oxygen partial pressure (temperature rise 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 temperature rise rate to the oxygen partial pressure in the second heat treatment step (temperature rise 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, from the viewpoint that the temperature rise rate can be increased to shorten the time until the end of the calcination, and that cracking of the molded body can be more effectively suppressed by combining it with other components (e.g., acrylic acid-based binders, etc.). The first heat treatment step is a temperature rise step, and can be rephrased as the first temperature rise step.

[0017] In one preferred embodiment, the ratio of the temperature rise rate to the oxygen partial pressure in the first heat treatment step (temperature rise rate / oxygen partial pressure) is 7°C / (atm min) or more and less than 500,000°C / (atm min). In another 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 4,000°C / (atm min). In another preferred embodiment, the ratio of the temperature rise rate to the oxygen partial pressure in the first heat treatment step and the second heat treatment step (temperature rise rate / oxygen partial pressure) is 25°C / (atm min) or more and 120,000°C / (atm min). 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 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, a method for producing a ceramic calcined body of the present invention can be mentioned.

[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 rise rate in the first heat treatment step may be a constant rate or may be varied within the above range. For example, in the first heat treatment step, when the temperature increase rate 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 one preferred embodiment, there is mentioned a method for producing a ceramic calcined body, in which 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 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 temperature rise rate to the oxygen partial pressure in at least one of the first heat treatment step or 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), thereby making it possible to increase the temperature rise rate and suppress the occurrence of defects.The reason why the ratio of the temperature rise rate to the oxygen partial pressure in at least one of the first heat treatment step or 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) is able to increase the temperature rise rate and suppress the occurrence of defects is not clear, but is thought to be as follows. In at least one of the first heat treatment step or the second heat treatment step, by increasing the heating rate under an atmosphere with a reduced oxygen partial pressure, 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, thereby preventing cracks, etc. from occurring 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, from the viewpoint that the occurrence of defects can be further suppressed by combining with other components (for example, an acrylic acid-based binder, etc.) and the time until the completion of calcination can be shortened by a high temperature rise rate. Moreover, the oxygen partial pressure is not particularly limited and may be more 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 of the present invention is a method for producing a ceramic calcined body, in which the oxygen partial pressure in the second heat treatment step is 0.11 atm or less. Another 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 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 herein 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 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, carbon monoxide CO gas diluted with nitrogen N, etc. 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, and is 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 shortening the time until the end of the calcination by a high heating rate. In a preferred embodiment, the oxygen concentration in the first heat treatment step is 0.3% or less, and the method for producing a ceramic calcined body is as described in the Examples below. The oxygen concentration can be measured 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 the organic material contained in the molded body is preferably 12% by mass or less, based on the total mass (100% by mass) of the ceramic molded body, and is more preferably 10% by mass, even more preferably 8% by mass or less, and particularly preferably 6% by mass or less, from the viewpoint of being able to shorten the time until the completion of calcination by a high heating rate while suppressing the occurrence of defects when the molded body is large. The content of the organic material is preferably 1% by mass or more, and is 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, from the viewpoint of being able to shorten the time until the completion of calcination by a high heating rate while suppressing the occurrence of defects when the molded body is large.

[0032] The shape of the molded body is not particularly limited, but examples include a rectangular parallelepiped shape, a disk shape, etc. Regarding the size of the molded body, the molded body is set to 2.7 cm in size in order to facilitate processing into a dental prosthesis of an artificial tooth corresponding to one natural tooth. 3 a rectangular parallelepiped having a volume of more than 19.0 cm and a thickness of more than 1 cm; 3 In the case of a rectangular solid-shaped molded body, it is preferable that the molded body has a volume of 3 cm or more and a thickness of 1 cm or more. 3 More preferably, it is 5 cm or more. 3 The volume is preferably 125 cm or more, but is not particularly limited thereto. 3 The thickness can be less than 1.2 cm. In the case of a rectangular solid-shaped molded body, 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, "disc-shaped" includes not only a circle but also a flat shape surrounded by a closed curve, such as an ellipse. In this specification, "rectangular solid" generally means a three-dimensional shape composed of six rectangular faces, but also includes a shape in which each ridge and / or vertex is composed of a curved surface, i.e., rounded (for example, a shape that has been subjected to fillet processing or R processing).

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

[0034] "Containing monoclinic zirconia as a main component" means that the proportion f of monoclinic zirconia represented by the following formula (1) is contained in the zirconia in the ceramic. m is 50% or more. m =I 28 / (I 28 +I 30 )×100 (1) (where f m represents the proportion (%) of monoclinic crystals, and in the XRD measurement, I 28 represents the integrated intensity of the peak at around 2θ = 28° where the main peak of the monoclinic system appears, and I 30 represents the area 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 (YO), cerium oxide (CeO), scandium oxide (ScO), niobium oxide (NbO), lanthanum oxide (LaO), erbium oxide (ErO), and praseodymium oxide (PrO, PrO). 11 Examples of the stabilizer include oxides such as samarium oxide (SmO), europium oxide (EuO), thulium oxide (TmO), gallium oxide (GaO), indium oxide (InO), and ytterbium oxide (YbO), and from the viewpoints of achieving superior effects of the present invention and particularly superior aesthetics, YO (yttria) and / or CeO are preferred. The stabilizers may be used alone or in combination of two or more.

[0038] The stabilizer content 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. A content of 2 mol% or more is preferable in that the crystalline form contained in the sintered body contains more cubic crystals, improving translucency. Furthermore, the stabilizer content 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. A content of 9 mol% or less is preferable because the proportion of cubic crystals contained in the crystalline form is not too high, which makes it easy to suppress grain growth, prevents the crystal structure from becoming too large, and suppresses a decrease in translucency. The stabilizer content may be within any combination 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 in the range of 3.7 to 8 mol%, if necessary.

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

[0040] In a preferred embodiment, the stabilizer capable of suppressing the phase transition of zirconia is yttria, and the ceramic contains zirconia and yttria that is not dissolved in the zirconia. y can be calculated based on the following formula (2): y =I 29 / (I 28 +I 29 +I 30 )×100 (2) (where f yrepresents the proportion (%) of undissolved yttria, and in the XRD measurement, I 28 represents the integrated intensity of the peak at around 2θ = 28° where the main peak of the monoclinic system appears, and I 29 represents the area intensity of the peak at 2θ=29° where the main peak of yttria appears, and I 30 represents the area intensity of the peak near 2θ = 30° where the main peak of the tetragonal or cubic crystal system appears.)

[0041] Undissolved yttria abundance f y From the viewpoint that the desired zirconia sintered body can be easily obtained, the abundance ratio f of undissolved yttria 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 also 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 content of yttria is 5.8 mol % or more and 8 mol % or less, f y can be 25% or less.

[0043] For example, when the content of yttria 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 yis 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 ZrO and HfO. In this specification, the phrase "the stabilizer is solid-dissolved" means, for example, that elements (atoms) contained in the stabilizer are solid-dissolved in ZrO and HfO.

[0045] The ceramic compact may further contain NbO from the viewpoint of machinability. Another preferred embodiment includes a method for producing a ceramic calcined body, in which the ceramic compact contains zirconia, a stabilizer capable of suppressing the phase transition of zirconia, NbO and / or TaO, and an organic material, wherein the total content of zirconia, the stabilizer, NbO, and TaO is 100 mol%, the zirconia content (total content of ZrO and HfO) is 78 to 97.5 mol%, the stabilizer content is 1 to 12 mol%, the total content of NbO and TaO is 1 to 9 mol%, and a Group I element is further contained. In the above embodiment, the zirconia sintered body (hereinafter referred to as a "zirconia composite sintered body") obtained by sintering the calcined body is machinable even in the sintered state, and has excellent machinability.

[0046] The content (mol %) of the Group I element in the compact is the external addition rate relative to the total of 100 mol % of zirconia, the stabilizer, NbO, and TaO. The content of the Group I element is a value calculated by converting the amount (mass) of the raw material charged when adding it into mol %.

[0047] In the above embodiment, the reason why the zirconia composite sintered body is machinable even in the sintered state is unclear, 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 NbO and / or TaO, the presence of a Group I element at the interface between zirconia particles (hereinafter also referred to as "grain boundary") is presumed to reduce the grain boundary strength, thereby facilitating particle separation and improving machinability. Furthermore, since NbO and / or TaO coarsen the microstructure of the zirconia composite sintered body and reduce its hardness, the Group I element and NbO and / or TaO work together to improve machinability. Therefore, the Group I element and NbO and / or TaO work together to provide the strength required for an artificial tooth while providing 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 compact 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 they are Group I elements. On the other hand, compared to Li, Na, K, Rb, Cs, and Fr have higher atomic weights, and as the atomic weight increases, the force acting in a 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 be lower. Therefore, when the Group I elements are K, Rb, Cs, and Fr, a smaller content range (e.g., 0.05 mol% to 1.0 mol%) can be selected, and when the Group I elements are Li and / or Na, a larger 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% relative to 100 mol% in total of zirconia, the stabilizer, NbO, and TaO. From the viewpoint of achieving better translucency and strength, the zirconia content 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, NbO, and TaO. 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 the sintered state, the total content of NbO and TaO in the compact is 1 to 9 mol%, preferably 1.5 mol% to 8.5 mol%, based on a total of 100 mol% of zirconia, the stabilizer, NbO, and TaO. In order to achieve superior machinability through cooperation with the Group I elements, the total content of NbO and TaO is more preferably 2.5 mol% to 8 mol%, and even more preferably 3 mol% to 7 mol%. When the total content of NbO and TaO is 1 mol% or more, sufficient machinability is likely to be achieved. Furthermore, when the total content of NbO and TaO is 9 mol% or less, the resulting zirconia composite sintered body is less susceptible to chipping and other defects, and sufficient physical properties are likely to be achieved.

[0053] The compact for obtaining the zirconia composite sintered body may further contain TiO2. The content of TiO2 is preferably more than 0 mass% and not more than 5.0 mass%, more preferably 0.01 mass% to 4.5 mass%, relative to 100 mass% of the total of zirconia, the stabilizer, Nb2O5, and Ta2O5. In view of the fact that TiO2 acts as a unit when combined with a Group I element and provides superior strength, the content is further preferably 0.6 mass% to 4.3 mass%, particularly preferably 0.7 mass% to 3.7 mass%, and most preferably 2.5 mass% to 3.5 mass%.

[0054] The content (mass%) of TiO2 is the external addition rate relative to the total of zirconia, the stabilizer, Nb2O5, and Ta2O5 (100 mass%). The content of TiO2 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 body of the present invention may optionally contain additives such as colorants (including pigments, composite pigments, and fluorescent agents), alumina (Al2O3), titanium oxide (TiO2), and silica (SiO2) (excluding the stabilizer). These components may be used alone or in combination. In a preferred embodiment, a method for producing a ceramic calcined body further containing TiO2 is described. Examples of the pigment include an oxide 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 YO3 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. By including a fluorescent agent in the molded body, the calcined body and the sintered body have fluorescence. The type of fluorescent agent is not particularly limited, and one or more fluorescent agents capable of emitting fluorescence with light of any wavelength can be used. Examples of fluorescent agents include those containing metal elements. Examples of such metal elements include Ga, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent may contain one of these metal elements alone, or two or more of them. Among these metal elements, Ga, Bi, Eu, Gd, and Tm are preferred, with Bi and Eu being more preferred. Examples of fluorescent agents include oxides, hydroxides, acetates, and nitrates of the above metal elements. The fluorescent agents are Y2SiO5:Ce, Y2SiO5:Tb, (Y, Gd, Eu)BO3, Y2O3:Eu, YAG:Ce, ZnGa2O4:Zn, 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 application 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 or more and 1% by mass or less, more preferably 0.005% by mass or more and 0.5% by mass or less, and even more preferably 0.01% by mass or more and 0.1% by mass or less.

[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 ceramic 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, even more 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 an atmosphere with an oxygen concentration of 12% or more, with nitrogen gas or the like flowing. 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, and 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, and is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 5 minutes or more. In addition, the time for 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 this facilitates the removal of combustion residues of organic materials.

[0066] Furthermore, the second heat treatment step preferably includes a temperature-raising step in which the molded body is heated 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 the second temperature-raising step. The temperature-raising rate in the second temperature-raising 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, from the viewpoint of suppressing the occurrence of defects and shortening the time until the completion of the calcination by a high temperature-raising rate. The temperature-raising rate in the second temperature-raising 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 increase rate in the second temperature increase 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 a constant rate or may be changed within the above range. For example, when the temperature increase rate is 5.0°C / min or more during 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 being able to shorten the time until completion of the calcination by a high temperature rise rate while suppressing the occurrence of defects.

[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, even more 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 one preferred embodiment, the method for producing a ceramic calcined body includes a step in which the second heat treatment step further includes a holding step in which the molded body is heated by holding the molded body at a constant temperature in the range of 500° C. to 1300° C. The second heat treatment step includes a temperature increase step, and by including a holding step in which the temperature is held at a constant temperature in addition to the temperature increase step, it is possible to effectively perform debinding while suppressing the occurrence of defects, and to shorten the time until the completion of calcination.

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

[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 embodiments including the holding step, the temperature reached in the first heat treatment step may be the holding temperature in the degreasing step. In some embodiments 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. Furthermore, in some embodiments including the holding step, the temperature reached in the first heat treatment step is preferably lower than the calcination temperature, 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) and then a temperature-raising step, as long as the effects of the present invention are achieved, or may have a temperature-raising step after the first heat treatment step, then a holding step of holding the molded body at a predetermined temperature, and then a temperature-raising 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 those in the calcination step. The temperature lowering rate is not particularly limited, but is 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 be changed depending on the embodiment, and the temperature lowering 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] The zirconia powder may be a commercially available zirconia powder. The stabilizer powder (e.g., yttria powder) may be a commercially available product, or may be ground in a known grinding / mixing device (e.g., a ball mill) before use.

[0080] Commercially available products include, for example, zirconia powder (trade name "Zpex (registered trademark)" (Y2O3 content: 3 mol%), "Zpex (registered trademark) 4" (Y2O3 content: 4 mol%), and "Zpex (registered trademark) Smile (registered trademark)" (YO content: 5.5 mol%), "TZ-3Y" (YO content: 3 mol%), "TZ-3YS" (YO content: 3 mol%), "TZ-4YS" (YO content: 4 mol%), "TZ-6Y" (YO content: 6 mol%), "TZ-6YS" (YO content: 6 mol%), "TZ-8YS" (YO content: 8 mol%), "TZ-10YS" (YO content: 10 mol%), and "TZ-3Y-E" (YO content: 3 mol%) Examples include "TZ-3YS-E" (YO content: 3 mol%), "TZ-3YB-E" (YO content: 3 mol%), "TZ-3YSB-E" (YO content: 3 mol%), "TZ-3YB" (YO content: 3 mol%), "TZ-3YSB" (YO content: 3 mol%), "TZ-3Y20AB" (YO content: 3 mol%), "TZ-8YSB" (YO content: 8 mol%), and "TZ-0" (YO content: 0 mol%); all manufactured by Tosoh Corporation. The commercially available zirconia powder also contains HfO. Commercially available zirconia powders containing YO in addition to zirconia can also be used. As the zirconia powder, zirconia powder in which YO is uniformly dispersed and solid-solved, such as the commercially available TZ series (product names containing "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, etc.

[0081] A mixture of zirconia powder and stabilizer powder is added to water to prepare a slurry, which is then pulverized (e.g., wet pulverized) in a pulverizer until the desired particle size is reached. The pulverized slurry is then dried and granulated. The resulting powder is then fired at a temperature (e.g., 800 to 1200°C) that does not cause the zirconia particles to sinter, producing a primary powder. The pulverizer used for pulverization is not particularly limited, and any known pulverizer, such as a ball mill, can be used. The method for drying the pulverized slurry is not particularly limited, but spray drying is preferred. For spray drying, any known spray dryer can be used. The average particle size of the primary powder is not particularly limited, but is preferably 0.2 μm or less, considering the translucency of the resulting sintered body. The average particle size can be determined by laser diffraction scattering. Specifically, the laser diffraction scattering method can be performed by using a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation) and measuring on a volume basis using a 0.2% aqueous solution of sodium hexametaphosphate as a dispersion medium.

[0082] The primary powder obtained as described above is added to water to prepare a slurry. The slurry is pulverized (e.g., wet pulverized) in a pulverizer until the desired particle size is reached, followed by mixing. 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 pulverized slurry, followed by drying to prepare a secondary powder. The organic material and other additives are typically added after pulverization, but 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 to prepare the primary powder. The average particle size of the secondary powder is not particularly limited, but is preferably 0.2 μm or less, for example, in terms of the translucency 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, they may be added to the obtained secondary powder. The type and content of ceramics (including the abundance of zirconia crystal systems), the type and content of stabilizers, and the type and content of organic materials in the raw material composition are the same as those in the molded body. Regarding the content of organic materials, "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 pressing pressure is set to an optimum value depending on the size, hardness, biaxial bending strength, particle size of the raw material powder, etc. of the target molded body, and is usually 5 MPa to 1000 MPa. By increasing the pressing pressure during molding in the above-mentioned production method, the pores of the obtained molded body are more fully filled, thereby increasing the density of the molded body. Furthermore, in order to increase the density of the obtained 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. Examples of batch type firing furnaces include a batch type electric furnace, and examples of continuous type firing furnaces include 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 removing the organic binder in the second heat treatment step and the calcination step in the presence of superheated steam. It is also possible to suppress rapid decomposition of the organic binder by applying heated steam to the molded body at a temperature that is approximately 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 time until the end of calcination due to a high heating rate (the time from the start of heating to the end of the holding time at the maximum temperature in the calcination step) can be shortened.

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

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

[0091] Hereinafter, the physical properties of the ceramic calcined body will be described using a zirconia calcined body as an example when the ceramic contains zirconia. Hereinafter, 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 zirconia calcined body is preferably 15 MPa or more to ensure strength that allows machining, and 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), but the only change is the size of the test specimen, which is measured using a 5 mm x 10 mm x 50 mm test specimen. The test specimen's face and C-face (the surface where the corners of the test specimen are chamfered at a 45° angle) are finished in the longitudinal direction with #600 sandpaper. The test specimen is positioned so that the widest surface faces vertically (the load direction). In the bending test, the support distance (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 press pressure used to produce the molded body, the content of the organic material (preferably an acrylic acid-based binder), the maximum temperature in the calcination process, and the holding time at that maximum temperature.

[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 350 HV 1 / 15 or less, the machinability (cuttability and grindability) is excellent and the rate of chipping can be reduced. "HV 1 / 15" means the Vickers hardness when held for 15 seconds at a load (test force) of 1 kgf.

[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 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 is preferably 2.9 to 3.6 g / cm 3 More preferably, it is 3.1 to 3.4 g / cm 3 It is more preferable that:

[0097] The density of the zirconia calcined body means 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. The density can then 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 adjusting the average particle size of the particles contained in the calcined body, the binder content, etc.

[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 the ceramic calcined body obtained by any of the above-mentioned production methods while maintaining 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 or the like).

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

[0102] The maximum firing temperature is preferably more than 1300° C., more preferably 1350° C. or higher, and even more preferably 1400° C. or higher. The maximum firing temperature is preferably 1650° C. or lower, more preferably 1600° C. or lower, and even more preferably 1580° C. or lower.

[0103] In the sintering step, there is no particular limitation on the sintering time (retention 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 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 rate and temperature decrease rate 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 depending on the performance of the firing furnace. The temperature increase rate to the maximum firing temperature can be, for example, 10°C / min or more, 50°C / min or more, 100°C / min or more, 120°C / min or more, 150°C / min or more, or 200°C / min or more. The temperature decrease rate is preferably set so as not to cause defects such as cracks in the sintered body. For example, after heating is completed, the sintered body can be allowed to cool at room temperature.

[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 caused by metal materials can be suppressed, resulting in excellent aesthetics. Furthermore, a manufacturing method can be selected appropriately depending on the application. 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.

[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 preparation method of the raw material composition used to prepare 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 as 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 in the 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 using a spray dryer to prepare granules (secondary powder). The prepared granules were used as the raw material composition to produce the zirconia molded bodies described below. The average particle size can be determined by laser diffraction scattering. Specifically, the laser diffraction scattering method can be performed by using a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation) and measuring on a volume basis using a 0.2% aqueous solution of sodium hexametaphosphate as a dispersion medium.

[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. 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 produce the zirconia molded body described below.

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

[0113]

[0114] In Table 1, the content of each component is as follows: The NaOH content (mol%) and the Al2O3 content (mol%) are externally added relative to a total of 100 mol% of zirconia, YO3, and Nb2O5. In Table 1, the TiO2 content (mass%) and the colorant content (mass%) are externally added relative to a total of 100 mol% of zirconia, YO3, and Nb2O5. In Table 1, the Nb2O5 content (mol%) is the content per 100 mol% of zirconia, YO3, and Nb2O5. The YO3 content (mol%) is the content per 100 mol% of zirconia, YO3, Al2O3, and Nb2O5.

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

[0116] Example 1 The zirconia molded body obtained as described above was heated to 600°C at the heating rate, under the atmospheric conditions, and in a test electric furnace as 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 as shown in Table 2. After the holding step, the body was further heated to 1000°C at the heating rate and under the atmospheric conditions of the second heat treatment step as shown in Table 2. Furthermore, calcination was carried out at a maximum temperature of 1000°C under the atmospheric conditions and holding time as shown in Table 3, to produce a zirconia calcined body. Figure 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] Zirconia calcined bodies were 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, 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 F-R", 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 cracks and cracks in zirconia calcined bodies] Ten zirconia calcined bodies were produced for each Example or Comparative Example, and the presence or absence of cracks and cracks on the surface of these zirconia calcined bodies was visually evaluated. If even one zirconia calcined body had a crack or crack on the surface, it was evaluated as "present," and if no cracks or cracks were present on the surface, it was evaluated as "absent." The results are shown in Table 4.

[0120] [Evaluation of Internal Residual Carbon in Zirconia Calcined Body] The zirconia calcined 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 whether no residual carbon was present was evaluated as "present." The results are shown in Table 4.

[0121] [Evaluation of Pass / Fail of Zirconia Calcined Body] A body that was evaluated as "None" in the [Evaluation of Cracks and Cracking in Zirconia Calcined Body], was evaluated as "None" in the [Evaluation of Internal Residual Carbon in 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 was evaluated as "Pass", and any other body was evaluated as "Fail".

[0122]

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

[0124]

[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.

[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.

[0127] 1. Oxygen concentration 2. Temperature

Claims

1. A method for producing a calcined ceramic body, comprising a heat treatment step of heating a ceramic compact, the heat treatment step comprising a first heat treatment step and a second heat treatment step, wherein 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 compact contains an organic material.

2. A method for producing a ceramic calcined body according to claim 1, wherein 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 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.

3. A method for producing a ceramic calcined body according to claim 2, further comprising a calcination step of heating the compact after the first heat treatment step, while 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. A method for producing a ceramic calcined body according to claim 3, wherein the second heat treatment step is carried out after the first heat treatment step and before the calcination step, and in the second heat treatment step, the molded body is heated in an atmosphere with an oxygen partial pressure of more than 0.12 atm.

5. The method for producing a ceramic calcined body according to claim 4, wherein the temperature rise rate in the second heat treatment step is 2.0°C / min or more.

6. A method for producing a ceramic calcined body according to claim 4 or 5, wherein the temperature range in the second heat treatment step is 500°C or higher and 1300°C or lower.

7. A method for producing a ceramic calcined body according to claim 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 the range of 500°C or higher and 1300°C or lower.

8. The method for producing a ceramic calcined body according to claim 1 or 2, wherein the organic material contains an acrylic acid-based binder.

9. The method for producing a calcined ceramic body according to claim 8, wherein the content of the organic material is 1 to 12 mass % relative to the total mass (100 mass %) of the ceramic compact.

10. 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 3. 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 10 ...

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

12. The method for producing a calcined ceramic body according to claim 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. A method for producing a calcined ceramic body according to claim 1 or 2, wherein the ceramic further contains TiO2.

14. A method for producing a ceramic calcined body according to claim 1 or 2, wherein the ceramic further contains Nb2O5.

15. The method for producing a ceramic calcined body according to claim 3, wherein the time for the calcination step is within the range of 1 minute to 1 hour.

16. A method for producing a ceramic calcined body according to claim 3 or 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. A method for producing a ceramic calcined body according to claim 1 or 2, wherein the ceramic calcined body is for producing a dental prosthesis.

18. A method for producing a sintered ceramic body, comprising a sintering step of sintering the calcined ceramic body obtained by the method of claim 1 or 2 at a maximum firing temperature exceeding 1200°C.

Images