Manufacturing method for sintered bodies

Abstract

To provide a production method of a sintered body that can obtain a sintered body satisfying light transmissivity required as a dental prosthetic material by short time sintering without essentially requiring precise temperature control at a high temperature region and without depending on a content of a stabilization element of a zirconia composition.SOLUTION: A production method of a zirconia sintered body containing a stabilization element comprises: a first temperature rising step for rising temperature of a zirconia composition containing the stabilization element from a temperature rising start temperature up to a first arrival temperature between 800°C or higher and lower than 1400°C with a rate of temperature increase of 150°C / minute or more; a second temperature rising step for rising the temperature from the first arrival temperature up to a second arrival temperature between 1400°C or higher and lower than 1580°C with a rate of temperature increase of over 30°C / minute and less than 200°C / minute; and a holding step for holding the temperature at the second arrival temperature.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing a sintered zirconia body, and more particularly to a method for manufacturing a sintered zirconia body in a short time. [Background technology]

[0002] Sintered bodies primarily composed of zirconia are used in dental prosthetic materials such as crowns and bridges. These sintered bodies achieve aesthetics equivalent to natural teeth through a sintering process that includes heating from room temperature to the maximum temperature, holding at the maximum temperature, and cooling down from the maximum temperature, requiring at least two hours of holding at the maximum temperature and a total of at least seven hours of sintering (hereinafter also referred to as "conventional sintering"). Therefore, the manufacture of these sintered bodies required a long sintering time.

[0003] In response to this, in recent years, a sintering method that requires less time for sintering compared to conventional sintering (hereinafter also referred to as "short-time sintering") has been investigated that can produce sintered bodies with the same aesthetic qualities as those obtained by conventional sintering (hereinafter also referred to as "conventional sintered bodies").

[0004] In short-time sintering, efforts are being made to shorten the time required for sintering by primarily improving the heating rate, thereby reducing the holding time at the maximum temperature. For example, Patent Document 1 discloses a short-time sintering method that includes a three-stage heating step. Patent Document 2 also discloses a short-time sintering method that includes a heating step in which the heating rate is increased until the temperature reaches 75% to 90% of the maximum temperature, and then the holding time at the maximum temperature is shortened by slowing down the heating rate thereafter. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2021 / 048674 [Patent Document 2] International Publication No. 2019 / 166938 [Overview of the project] [Problems that the invention aims to solve]

[0006] The short-time sintering method described in Patent Document 1 requires switching the heating rate in the high-temperature region exceeding 1200°C, and furthermore, because the densification behavior due to sintering proceeds rapidly in the high-temperature region exceeding 1200°C, precise temperature control is necessary. However, switching the heating rate in the high-temperature region is difficult because the heater of the sintering furnace cannot keep up with the heating program, and furthermore, sintering furnaces that can handle such control are limited to special firing furnaces. In addition, the sintered body obtained by the short-time sintering method described in Patent Document 2 has lower light transmittance compared to a conventionally sintered body and does not possess the light transmittance required for dental prosthetic materials. Moreover, in the method of Patent Document 2, the light transmittance of a sintered body of stabilized zirconia with a high yttrium content is particularly reduced compared to a conventionally sintered body.

[0007] The present disclosure aims to provide a method for producing a sintered zirconia body by short-time sintering, which allows for obtaining a sintered body having the translucency required for dental prosthetic materials, without requiring precise temperature control in the high-temperature range and regardless of the content of stabilizing elements in the zirconia composition. [Means for solving the problem]

[0008] The inventors focused on the heating process in short-time sintering. As a result, they found that by heating to the maximum achievable temperature at a specific heating rate and target temperature, it is possible to obtain a sintered body that exhibits the same aesthetic properties as conventionally sintered bodies without requiring precise temperature control in the high-temperature range. Furthermore, they found that this manufacturing method can produce a sintered zirconia body with the translucency required for dental prosthetics, regardless of the content of stabilizing elements in the zirconia composition.

[0009] In other words, the present invention is as claimed, and the gist of this disclosure is as follows. [1] A method for producing a sintered zirconia body containing a stabilizing element, comprising: a first heating step of heating a zirconia composition containing a stabilizing element from a heating start temperature to a first target temperature of 800°C or more and less than 1400°C at a heating rate of 150°C / min or more; a second heating step of heating from the first target temperature to a second target temperature of 1400°C or more and less than 1580°C at a heating rate of more than 30°C / min and less than 200°C / min; and a holding step of holding the composition at the second target temperature. [2] The manufacturing method according to [1] above, wherein the holding time in the holding step is less than 20 minutes. [3] The manufacturing method according to [1] or [2] above, wherein the difference between the second temperature reached and the first temperature reached is 300°C or more and 600°C or less. [4] The manufacturing method according to any one of [1] to [3] above, wherein the rate of heating to the second temperature is 0.15 or more and 1.0 or less relative to the rate of heating to the first temperature. [5] The manufacturing method according to any one of [1] to [4] above, wherein the temperature at which the heating starts is any temperature from room temperature to 500°C. [6] A manufacturing method according to any one of [1] to [5] above, comprising a cooling step of cooling the sintered body from the second attainable temperature to any cooling temperature of 800°C to 1200°C and removing the sintered body from the sintering furnace. [7] The manufacturing method according to [6] above, wherein the removed sintered body is cooled in an atmospheric atmosphere by at least one of natural cooling and blowing of a cooling gas. [8] The manufacturing method according to [6] or [7] above, wherein the cooling gas is one or more selected from the group consisting of air, argon, nitrogen, and helium. [9] The manufacturing method according to any one of [1] to [8] above, wherein the material is sintered using a sintering furnace equipped with a heater consisting of one or more selected from the group consisting of molybdenum disilicide, silicon carbide, lanthanum chromite and carbon.

[10] The manufacturing method according to any one of [1] to [9] above, wherein the composition is a molded or calcined zirconia body.

[11] The manufacturing method according to any one of [1] to

[10] above, wherein the stabilizing element is one or more selected from the group consisting of yttrium, calcium, cerium, magnesium, praseodymium, ytterbium, erbium, and terbium.

[12] The manufacturing method according to any one of [1] to

[11] above, wherein the content of the stabilizing element is 2.5 mol% or more and 8 mol% or less.

[13] The manufacturing method according to any one of [1] to

[12] above, wherein the T+C phase ratio of the composition is 65% or more.

[14] The manufacturing method according to any one of [1] to

[13] above, wherein the composition comprises a transition metal element other than zirconium and hafnium, and at least one of the lanthanide rare earth elements as a coloring element. [Effects of the Invention]

[0010] This disclosure aims to provide a method for manufacturing a sintered body by short-time sintering, which does not require precise temperature control in the high-temperature range and yields a sintered body that satisfies the translucency required for dental prosthetic materials, regardless of the content of stabilizing elements in the zirconia composition. [Modes for carrying out the invention]

[0011] The method for manufacturing a sintered body according to this disclosure will be described with reference to an example of an embodiment. The terms used in this embodiment are as follows. Any combination of the components and parameters disclosed herein is possible, and any combination of the upper and lower limits of the values ​​disclosed herein is also possible.

[0012] "Composition" refers to a substance having a certain composition, and examples include one or more selected from the group consisting of powder, molded body, calcined body, and sintered body. "Zirconia composition" refers to a composition mainly composed of zirconia, and more specifically, a composition consisting essentially of zirconia.

[0013] "Powder" refers to a composition that is an aggregate of powder particles (at least one of primary and secondary particles) and is fluid. "Zirconia powder" refers to a powder whose main component is zirconia, and is essentially a powder made of zirconia. Furthermore, "powder composition" refers to a composition composed of powders with different characteristics, and in particular, a composition containing powders with different compositions.

[0014] "Granular powder" refers to a composition that is an aggregate of powder particles (granular particles) and is fluid, and in particular, a composition in which the powder particles are slowly aggregated. "Zirconia granular powder" refers to a granular powder whose main component is zirconia, and is essentially a granular powder made of zirconia.

[0015] A "molded body" is a composition having a certain shape, composed of powder particles aggregated by physical force, and in particular, a composition that has not undergone heat treatment after the shape has been imparted (e.g., after molding). A "zirconia molded body" is a molded body whose main component is zirconia, and is essentially a molded body made of zirconia. Furthermore, molded bodies are used interchangeably with "compacted bodies".

[0016] A "calcined body" is a composition having a certain shape and composed of fused particles, which has been heat-treated at a temperature below the sintering temperature. A "zirconia calcined body" is a calcined body whose main component is zirconia, and is essentially a calcined body made of zirconia.

[0017] A "sintered body" is a composition having a certain shape and composed of crystalline particles, and is a composition in a state that has been heat-treated at a temperature above the sintering temperature. A "zirconia sintered body" is a sintered body whose main component is zirconia, and is essentially a sintered body made of zirconia.

[0018] The "main component" is the component that constitutes the main phase (matrix, base material, parent phase) in the composition of the composition, and preferably has a mass percentage of 75% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, or 99% by mass or more, and is a component that is 100% by mass or less or less by mass.

[0019] A "stabilizing element" is an element that stabilizes the crystalline phase of zirconia by being dissolved in it.

[0020] The content of stabilizing elements in a composition (mol%) (hereinafter also referred to as "amount of stabilizing elements") is the molar ratio of stabilizing elements in oxide form to the total amount of zirconium in ZrO2 form and stabilizing elements in oxide form in the composition.

[0021] "BET specific surface area" is the specific surface area [m²] measured by the BET multi-point method (5 points) using nitrogen as the adsorbent gas, in accordance with JIS R 1626. 2 This is the BET specific surface area measured under the following conditions: [ / g]. Adsorption medium: N2 Adsorption temperature: -196℃ Pretreatment conditions: Degassing treatment at 250°C for at least 1 hour in an air atmosphere.

[0022] The BET specific surface area can be measured using a general-purpose specific surface area measuring device (e.g., Tristar II 3020, manufactured by Shimadzu Corporation). The calcined body should be processed into a rectangular parallelepiped shape of 5 mm × 5 mm × 16 mm, and then all surfaces of the rectangular parallelepiped should be polished with sandpaper of grit #400 in accordance with JIS R 6001-2 to be used as the measurement sample.

[0023] "Average particle size" is the D in the volume particle size distribution of powder measured by the wet method. 50Therefore, it can be measured using a general-purpose instrument (for example, MT3300EXII, manufactured by Microtrac-Bell). The sample to be measured should be a slurry prepared by dispersing powder, from which slow aggregation has been removed by dispersion treatment such as sonication, in pure water. When measuring the volume particle size distribution by the wet method, it is preferable to measure the slurry at a pH of 3 to 6.

[0024] "Average granule size" is the volume particle size distribution of granular powder measured by the dry method. 50 Therefore, it can be measured using a general-purpose instrument (for example, the MT3100II, manufactured by Microtrac-Bell). The sample to be measured should be granular powder in a slowly aggregated state, without any dispersion treatment such as sonication.

[0025] A "powder X-ray diffraction pattern" is an XRD pattern obtained by smoothing and removing background noise from the XRD pattern of a composition obtained by powder X-ray diffraction (hereinafter also referred to as "XRD") measurement under the following conditions using an analysis program attached to the X-ray diffractometer (for example, integrated powder X-ray analysis software PDXL Ver.2.2, manufactured by RIGAKU Corporation). Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 2° / min Measurement range: 2θ = 26° ~ 33° 2θ = 72°~76° Acceleration voltage / current: 40mA / 40kV Divergence vertical limiting slit: 10mm Divergence / Induction Slit: 1° Light-receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185mm

[0026] XRD measurements can be performed using a general-purpose X-ray diffractometer (e.g., Ultima IV, manufactured by RIGAKU). The calcined body is prepared by polishing the surface with #400 grit sandpaper conforming to JIS R 6001-2, then lapping it with a 3 μm grit diamond abrasive, and the surface after lapping is then measured using XRD.

[0027] An "XRD peak" is a peak with a peak top at 2θ detected in the XRD pattern obtained in the above-described XRD measurement. In this embodiment, "not having an XRD peak" means that the XRD peak is not detected in the above-described XRD measurement.

[0028] The XRD peaks corresponding to each crystal plane of zirconia are those with peak tops at the following 2θ. XRD peak corresponding to the monoclinic (111) plane: 2θ = 31 ± 0.5° XRD peak corresponding to the monoclinic (11-1) plane: 2θ = 28 ± 0.5° XRD peak corresponding to the tetragonal (111) plane: 2θ = 30 ± 0.5° XRD peak corresponding to the cubic (111) plane: 2θ = 30 ± 0.5°

[0029] The XRD peaks corresponding to the tetragonal (111) plane and the XRD peaks corresponding to the cubic (111) plane are measured as a single overlapping peak.

[0030] "T+C phase ratio" refers to the proportion of tetragonal and cubic phases in the crystalline structure of zirconia. It is the ratio of the area intensity of the tetragonal and cubic zirconia XRD peaks to the total area intensity of the tetragonal, cubic, and monoclinic zirconia XRD peaks in the XRD pattern obtained in the above-mentioned XRD measurement, and can be calculated using the following formula. f T+C =[I t (111)+I c (111)] / [I m (111)+Im (11 - 1)+I t (111)+I c (111)]

[0031] In the above formula, f T+C is the tetragonal and cubic ratio, I t (111) is the area intensity of the (111) plane of the tetragonal crystal, I c (111) is the area intensity of the (111) plane of the cubic crystal, I m (111) is the area intensity of the (111) plane of the monoclinic crystal, I m (11 - 1) is the area intensity of the (11 - 1) plane of the monoclinic crystal, and I t (111)+I c (111) corresponds to the area intensity of the XRD peak having a peak top at 2θ = 30 ± 0.5°.

[0032] The area intensity of each XRD peak is a value obtained by analyzing the XRD pattern using an analysis program attached to the X - ray diffractometer (for example, integrated powder X - ray analysis software PDXL Ver.2.2, manufactured by Rigaku Corporation).

[0033] The "density of the molded body" is the measured density of the molded body [g / cm 3 , which is the mass [g] of the molded body obtained by mass measurement using a balance with respect to the volume [cm 3 of the molded body obtained by measuring the volume with a caliper and calculating from the dimensions.

[0034] The "density of the calcined body" is the measured density of the calcined body [g / cm 3 , which is the mass [g] of the calcined body obtained by mass measurement using a balance with respect to the volume [cm 3 of the calcined body obtained by measuring the volume with a caliper and calculating from the dimensions.

[0035] Vickers hardness is a value measured using a standard Vickers tester (e.g., Q30A, Qness) equipped with a diamond square pyramidal indenter. The measurement is performed by statically pressing the indenter into the surface of the sample and measuring the diagonal length of the indentation formed on the sample surface. Using the obtained diagonal length, the Vickers hardness can be calculated using the following formula.

[0036] Hv=F / {d 2 / 2sin(α / 2)} In the above equation, Hv is the Vickers hardness (HV), F is the measured load (1 kgf), d is the diagonal length of the indentation (mm), and α is the angle of the indenter (136°).

[0037] The following conditions can be used to measure Vickers hardness: Measurement sample: Disc-shaped object with a thickness of 3.0 ± 0.5 mm Measured load: 1 kgf

[0038] Prior to measurement, the sample should be pre-treated by polishing the measurement surface with #800 grit waterproof abrasive paper to remove any irregularities exceeding 0.1 mm.

[0039] "Total light transmittance" is the ratio [%] of transmitted light (sum of linearly transmitted light and diffusely transmitted light) to incident light, measured in accordance with JIS K 7361-1 for a sample with a thickness of 1.0 ± 0.1 mm. The sample used is a disc-shaped sintered body with a thickness of 1.0 ± 0.1 mm and a surface roughness Ra ≤ 0.02 μm on both sides. The measuring device should be a haze meter equipped with a D65 light source (for example, haze meter NDH4000, manufactured by Nippon Denshoku Co., Ltd.).

[0040] "Biaxial bending strength" is a value determined by a two-point bending test in accordance with JIS T 6526. To measure biaxial bending strength, a circular sintered body with a diameter of 14.5 mm ± 0.5 mm and a thickness of 1.25 mm ± 0.05 mm is used as the measurement sample, and the average value of 10 measurements with a support circle radius of 6 mm and an indenter radius of 0.7 mm is taken as the biaxial bending strength of the sintered body.

[0041] "Atmospheric pressure sintering" is a method of sintering a material (such as a molded body or calcined body) by heating it at a temperature above the temperature at which zirconia sintering progresses (hereinafter also referred to as the "sintering temperature") without applying any external force to the material during sintering. "Atmospheric pressure firing" is a method of heating a workpiece without applying external force during heat treatment, and in particular, it is a method of heating a workpiece at a temperature below the sintering temperature without applying external force during the calcination process.

[0042] [Method for manufacturing sintered bodies] The manufacturing method of this embodiment is a method for manufacturing a sintered zirconia body containing stabilizing elements, comprising: a first heating step of heating a zirconia composition containing stabilizing elements from a heating start temperature to a first target temperature of 800°C to less than 1400°C at a heating rate of 150°C / min or more; a second heating step of heating from the first target temperature to a second target temperature of 1400°C to less than 1580°C at a heating rate of more than 30°C / min but less than 200°C / min; and a holding step of holding at the second target temperature. With this manufacturing method, a sintered body with light transmittance equivalent to that of a normally sintered body can be obtained while shortening the holding time at the second target temperature compared to the holding time required for normal sintering, and with almost no influence from the amount of stabilizing elements. This effect is particularly pronounced in zirconia with a high amount of stabilizing elements. One reason why the light transmittance of the sintered body obtained by the manufacturing method of this embodiment is almost unaffected by the amount of stabilizing elements is that the influence of differences in grain growth rate during sintering, which originates from differences in the amount of stabilizing elements, is suppressed by going through the first heating step and the second heating step. As a result, pore elimination within the zirconia composition is more easily promoted, and it is conceivable that pore elimination within the composition is also promoted even in compositions with a high amount of stabilizing elements that result in a fast grain growth rate during sintering.

[0043] In this embodiment, the first heating step involves heating the zirconia composition containing stabilizing elements from the heating start temperature to a first target temperature of 800°C to less than 1400°C at a heating rate of 150°C / min or more (hereinafter, the first target temperature will also be referred to as "T1", and the heating rate from the heating start temperature to T1 will also be referred to as "HR1"). If HR1 is less than this, it will take too long to reach the temperature at which sintering progresses significantly. In addition, by satisfying this rate, the composition is heated uniformly, and temperature variations between the inside and surface of the composition are reduced. This facilitates the progress of sintering in the second heating step described later and the associated pore removal. Furthermore, the time required for heating can be shortened. As a result, a sintered body can be obtained with a shorter holding time compared to the holding time at the highest target temperature of normal sintering, and with light transmittance equivalent to that of a normally sintered body, regardless of the amount of stabilizing elements. The first heating step can be performed by placing the composition in a sintering furnace.

[0044] The starting temperature for the heating process can be any temperature before the composition begins to shrink during sintering, and is preferably any temperature from room temperature (20±20℃) to 500℃, preferably any temperature from room temperature to 100℃. To simplify temperature control and to further suppress temperature unevenness between the surface and the interior of the composition at the start of the second heating process, it is preferable that the starting temperature for the first heating process be room temperature.

[0045] From the viewpoint of further shortening the time required for the first heating step, examples of HR1 include 180°C / min or more, 200°C / min or more, or 230°C / min or more, and the upper limit of HR1 may be 500°C / min or less, 400°C / min or less, 300°C / min or less, or 280°C / min or less. Preferably, HR1 is 180°C / min or more and 500°C / min or less, 200°C / min or more and 400°C / min or less, 230°C / min or more and 300°C / min or less, or 230°C / min or more and 280°C / min or less. It is preferable that the heating rate (HR1) does not fluctuate (±2°C / min, preferably ±1°C / min) during the heating from the heating start temperature to T1.

[0046] T1 is a temperature between 800°C and 1400°C. Preferably, T1 is less than 1400°C and is one of the following temperatures: 1300°C or lower, 1200°C or lower, 1170°C or lower, 1150°C or lower, 1100°C or lower, or 1050°C or lower. If T1 is 1400°C or higher, a sintered body with lower light transmittance compared to a normal sintered body is obtained when the amount of stabilizing elements is high.

[0047] Furthermore, by setting T1 to 850°C or higher, preferably 950°C or higher, or 1000°C or higher, a sintered body can be manufactured without requiring excessive time for sintering. Preferred T1 ranges include 850°C to 1300°C, 950°C to 1200°C, or 1000°C to 1050°C. When T1 is within this range, coarse pores are less likely to be incorporated into the composition, and pores are efficiently removed in the second heating step.

[0048] Since T1 is the switching temperature from HR1 to HR2, it is not necessary to hold the temperature at T1. However, it is possible to hold the temperature at T1 as long as the effectiveness of the manufacturing method of this embodiment is not impaired. When holding the temperature at T1, examples include 0 minutes to 5 minutes, or 0 minutes to 15 seconds.

[0049] The second heating step involves heating from T1 to a second target temperature of 1400°C or higher but less than 1580°C at a heating rate of more than 30°C / min but less than 200°C / min (hereinafter, the second target temperature will be referred to as "T2", and the heating rate from T1 to T2 will also be referred to as "HR2"). The second heating step does not require switching the heating rate from above T1 to T2. Because precise temperature control (control of heating rate) in the high-temperature range is not required, the manufacturing method of this embodiment can be applied as a manufacturing method using a sintering furnace equipped with a general-purpose heater. In the temperature range above 1400°C, zirconia sintering proceeds rapidly, and the sintering behavior differs depending on the composition and physical properties of the composition. Therefore, it is difficult to switch the heating rate in the temperature range above 1400°C according to the characteristics of the composition. In the manufacturing method of this embodiment, there is no switching of the heating rate during the heating process from 1400°C to T2, nor is there any switching of the heating rate during the heating process from T1 to T2. Therefore, the heating rate does not change from 1200°C to T2, and a highly translucent sintered body can be obtained with a simple heating program.

[0050] In the second heating step, pores are gradually eliminated from the inside of the composition, resulting in a shape where pores are mainly located near the surface. Therefore, HR2 can be 150°C / min or less, 100°C / min or less, 80°C / min or less, or 60°C / min or less. On the other hand, from the viewpoint of shortening the sintering time, HR2 can be 33°C / min or more, 35°C / min or more, or 40°C / min or more, with 33°C / min to 150°C / min or 35°C / min to 80°C / min being preferred. Within these ranges of HR2, a sintered body with higher light transmittance can be obtained in compositions with a lower amount of stabilizing elements as the heating rate increases. Conversely, a sintered body with higher light transmittance can be obtained in compositions with a lower amount of stabilizing elements as the heating rate decreases. Since a sintered body with high light transmittance is more easily obtained regardless of the amount of stabilizing elements, HR2 is preferably 40°C / min to 180°C / min, and even more preferably 45°C / min to 120°C. It is preferable that the heating rate (HR2) from T1 to T2 does not fluctuate (±2°C / min, preferably ±1°C / min).

[0051] Preferably, HR1 > HR2, and more preferably, the ratio of HR2 to HR1 (hereinafter also referred to as "HR2 / HR1") is 0.15 or more and 1.0 or less, and more preferably 0.2 or more and 0.5 or less.

[0052] T2 is the maximum temperature reached in the manufacturing method of this embodiment, and is between 1400°C and 1580°C. Having T2 within this range allows for the elimination of pores through grain growth of zirconia crystal particles. This results in a sintered body that satisfies the translucency required for dental prosthetics, regardless of the amount of stabilizing elements, even with short sintering times. In addition, having a maximum temperature below 1580°C suppresses the deterioration of sintering furnaces equipped with general-purpose heaters such as molybdenum silicide (MoSi2) heaters or silicon carbide (SiC) heaters. For example, silicon carbide deteriorates above 1580°C. Therefore, having T2 within this range allows for the production of a sintered body with translucency similar to that of a conventional sintered body while suppressing the deterioration of the silicon carbide heater.

[0053] To make it easier to obtain a sintered body that meets the mechanical strength requirements for dental prosthetic materials, T2 can be 1450°C or higher, 1480°C or higher, or 1500°C or higher, and also 1570°C or lower, 1565°C or lower, 1560°C or lower, or less than 1560°C. In the manufacturing method of this embodiment, it is preferable that the pores of the composition exist near the surface before reaching T2. From this viewpoint, T2 is preferably 1500°C or higher, and more preferably 1510°C or higher. This makes it possible to obtain a sintered body with light transmittance equivalent to that of a normal sintered body even if the holding time at T2 is short, such as 15 minutes or less, and more preferably 10 minutes or less. T2 is preferably 1500°C or higher and 1565°C or lower, or 1500°C or higher and less than 1560°C.

[0054] The difference between T2 and T1 is T2 > T1, and furthermore, the temperature ranges are 150°C to less than 780°C, 200°C to less than 780°C, 300°C to 600°C, and 500°C to 600°C.

[0055] Therefore, it is believed that the first and second heating processes function not only as processes aimed solely at raising the temperature to T2, but also as pore removal processes that create a structure in the sintered material that facilitates pore removal.

[0056] In addition, the manufacturing method of this embodiment does not require prior to understanding the details of the sintering shrinkage behavior of the composition, such as the temperature and sintering rate to reach a specific density, and the composition can be sintered by controlling the sintering temperature program. Therefore, it is suitable as a manufacturing method for producing a wide variety of sintered bodies, including dental prosthetic materials, which have very large individual differences from patient to patient.

[0057] The manufacturing method of this embodiment includes a holding step of holding at T2. The manufacturing method of this embodiment is a sintering method having two heating steps: a first heating step and a second heating step. As a result, it is thought that pores inside the composition move to the surface, and by the time T2 is reached, the pores are located near the surface. Therefore, even if the holding time at T2 is short, pores near the surface of the composition are eliminated, and a sintered body with light transmittance equivalent to that of a normal sintered body is obtained.

[0058] The holding time in the holding step may be 1 minute or more, 3 minutes or more, or 5 minutes or more. A shorter holding time is preferable in order to shorten the time required for the manufacturing method of this embodiment and to reduce the energy consumption required for the manufacturing method of this embodiment. Examples of upper limits for the holding time include 30 minutes or less, 20 minutes or less, less than 20 minutes, or 15 minutes or less. A short holding time at the highest temperature reached is preferable, and if T2 is 1500°C or higher, and even more preferably 1510°C or higher, the translucency of the sintered body obtained will not decrease even if the holding time at T2 is short. For this reason, a holding time at T2 of 1 minute or more and less than 20 minutes is preferable. Furthermore, within these holding time ranges, a shorter holding time will result in a sintered body with higher translucency in compositions with a lower amount of stabilizing elements. On the other hand, a longer holding time will make it easier to obtain a sintered body with higher translucency in compositions with a higher amount of stabilizing elements. Since a sintered body with high translucency is more easily obtained regardless of the amount of stabilizing elements, a holding time of 1 minute or more and 15 minutes or less is preferable, and 5 minutes or more and 15 minutes or less is more preferable.

[0059] In the manufacturing method of this embodiment, a sintered body is obtained by going through a holding step. The sintered body after the holding step can be cooled by any method that can obtain the desired sintered body, and the sintered body can be recovered from the sintering furnace. The manufacturing method of this embodiment preferably has a cooling step of cooling from T2 to any cooling temperature of 800°C to 1200°C (hereinafter also referred to as "T3"), more preferably has a cooling step of cooling from T2 to T3 and removing the sintered body from the sintering furnace, and even more preferably has a cooling step of cooling the removed sintered body in an atmospheric atmosphere by natural cooling and blowing a cooling gas.

[0060] To further shorten the cooling time, the cooling rate from T2 to T3 (hereinafter also referred to as "CR1") is 30°C / min or more, 40°C / min or more, 45°C / min or more, or 50°C / min or more. Furthermore, CR1 can be exemplified as 200°C / min or less, 150°C / min or less, 100°C / min or less, or 80°C / min or less, which reduces the likelihood of defects such as cracking occurring during cooling. CR1 is preferably 30°C / min or more and 200°C / min or less, or 45°C / min or more and 80°C / min or less, and it is preferable that the cooling rate (CR1) does not fluctuate (±2°C / min, preferably ±1°C / min) during the cooling from T2 to T3.

[0061] The sintered body can be removed from the sintering furnace after cooling to T3. Cooling to T3 suppresses the occurrence of defects due to thermal shock, even when the sintered body is removed from the furnace and exposed to ambient air at room temperature, and also suppresses color changes in sintered bodies containing coloring elements during cooling. T3 is 800°C or higher or 850°C or higher, and can also be any of the following temperatures: 1200°C or lower, 1100°C or lower, 1050°C or lower, or 950°C or lower, with 800°C or higher and 1100°C or lower being preferred. Since the resulting sintered body is less likely to change color, T3 is more preferably 800°C or higher and less than 1000°C, and even more preferably 850°C or higher and 950°C or lower.

[0062] The removed sintered body is further cooled. The sintered body should be cooled to a temperature that can be handled (for example, below 100°C, or even to room temperature). Because this tends to reduce the variation in strength between sintering lots of the resulting sintered body, the sintered body removed from the sintering furnace should be cooled at an average cooling rate from T3 to 400°C (hereinafter referred to as "CR2"). (AVE) It is also called ) but it is more preferable to cool it to 300°C / min or more, 350°C / min or more, or 400°C / min or more. Also, CR2 (AVE) The temperature may be 800°C / min or less, 700°C / min or less, 600°C / min or less, or 500°C / min or less. CR2 (AVE)It is even more preferable to cool the temperature to 300°C / min to 800°C / min, 350°C / min to 600°C / min, or 400°C / min to 600°C / min. Since the sintering program of the firing furnace does not use the cooling down to 400°C in T3, the cooling rate may vary.

[0063] CR2 (AVE) This can be calculated by placing a general thermocouple thermometer (e.g., testo735-1, manufactured by Testo) in contact with the surface of the sintered body and measuring the time it takes for the temperature to rise from T3 to 400°C, then using the formula {(T3-400)[°C] / time from T3 to 400°C[minutes]}.

[0064] Such CR2 (AVE) Therefore, the sintered body removed from the sintering furnace may be allowed to cool naturally, but it is preferable to cool it by blowing a cooling gas onto it. Examples of the cooling gas include one or more selected from the group consisting of air, argon (Ar), nitrogen (N2), and helium (He), and also air.

[0065] The sintered body, which has been cooled to 400°C, can be cooled to any desired temperature by any method, such as natural cooling or blowing a cooling gas onto it.

[0066] The time required for the rapid cooling process can be 30 seconds or more, 1 minute or more, 2 minutes or more, or 3 minutes or more, and can also be 10 minutes or less, 8 minutes or less, or 5 minutes or less, with 30 seconds to 10 minutes or less, 1 minute to 8 minutes or less, or 3 minutes to 5 minutes or less being preferred.

[0067] Thus, the method for producing a sintered zirconia body comprises a first heating step of heating a zirconia composition containing stabilizing elements from a heating start temperature to T1 at a heating rate of 150°C / min or more, a second heating step of heating from T1 to T2 at a heating rate of more than 30°C / min but less than 200°C / min, and a holding step of holding at T2, and the sintered body is obtained by sintering the composition using a sintering furnace.

[0068] Furthermore, temperature control during the first heating step, the second heating step, the holding step, and the cooling from T2 to T3 can be performed by the sintering program of the sintering furnace used for sintering.

[0069] The sintering methods applicable to the manufacturing method of this embodiment include one or more selected from the group consisting of vacuum sintering, pressure sintering, and atmospheric pressure sintering, and more specifically, at least one of pressure sintering and atmospheric pressure sintering. However, the sintering method in the manufacturing method of this embodiment is preferably atmospheric pressure sintering, and more preferably atmospheric pressure sintering alone.

[0070] The atmosphere in the manufacturing method of this embodiment, that is, the atmosphere in the first heating step, the second heating step, the holding step, and the cooling step, is preferably an oxidizing atmosphere, and more preferably an atmospheric atmosphere.

[0071] The sintering furnace that can be used in the manufacturing method of this embodiment is arbitrary, but may be one or more selected from the group consisting of resistance heating furnaces, induction heating furnaces, high-frequency furnaces and IH furnaces, or further, one or more selected from the group consisting of resistance heating furnaces, induction heating furnaces and IH furnaces. The manufacturing method of this embodiment is more preferably a manufacturing method in which sintering is performed in a firing furnace that is at least one of a resistance heating furnace and an induction heating furnace.

[0072] The sintering furnace used for sintering is preferably a sintering furnace equipped with a general-purpose heater (heating element), a sintering furnace equipped with a heater consisting of one or more selected from the group consisting of molybdenum disilicate (MoSi2), silicon carbide (SiC), lanthanum chromite (LaCrO3), and carbon (C), and a sintering furnace equipped with a heater consisting of at least one of molybdenum disilicate and silicon carbide. Since it is commonly used in firing furnaces for dental prosthetic materials, the manufacturing method of this embodiment is preferably a manufacturing method that uses a sintering furnace equipped with one or more selected from the group consisting of molybdenum disilicate, silicon carbide, lanthanum chromite, and carbon for sintering, and more preferably a manufacturing method that uses a sintering furnace equipped with a silicon carbide heater for sintering.

[0073] The time required for the manufacturing method of this embodiment (particularly from the first heating step to the rapid cooling step) is 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, or 35 minutes or more, and can also be 55 minutes or less, 50 minutes or less, 45 minutes or less, or 40 minutes or less, and is preferably 15 minutes or more and 55 minutes or less, 25 minutes or more and 50 minutes or less, 30 minutes or more and 45 minutes or less, or 35 minutes or more and 40 minutes or less.

[0074] The manufacturing method of this embodiment is suitable as a method for manufacturing a zirconium sintered body, and moreover, as a method for manufacturing a zirconia sintered body for dental prosthetics. Furthermore, the manufacturing method of this embodiment is suitable as a method for manufacturing a zirconia sintered body containing yttrium, and is particularly suitable as a method for manufacturing a zirconia sintered body containing yttrium with a yttrium content of 2.8 mol% to 6 mol%, furthermore, as a method for manufacturing a zirconia sintered body containing yttrium with a yttrium content of 4 mol% to 6 mol%, and furthermore, as a method for manufacturing a zirconia sintered body containing yttrium with a yttrium content of 4.5 mol% to 6 mol%.

[0075] Furthermore, this embodiment may be considered as a sintering program for sintering a zirconia composition containing a stabilizing element, which includes a first heating step of raising the temperature from the sintering start temperature to a first target temperature of 800°C or more and less than 1400°C at a heating rate of 150°C / min or more, a second heating step of raising the temperature from the first target temperature to a second target temperature of 1400°C or more and less than 200°C / min at a heating rate of more than 30°C / min and less than 200°C / min, and holding the composition at the second target temperature.

[0076] Furthermore, this embodiment may be considered as a sintering method that includes, in a program for sintering a zirconia composition containing a stabilizing element, a first heating step of raising the temperature from the sintering start temperature to a first target temperature of 800°C or more and less than 1400°C at a heating rate of 150°C / min or more; a second heating step of raising the temperature from the first target temperature to a second target temperature of 1400°C or more and less than 200°C / min at a heating rate of more than 30°C / min and less than 200°C / min; and holding the temperature at the second target temperature.

[0077] [Composition] The composition used in the manufacturing method of this embodiment is a composition mainly composed of zirconia. Zirconia may contain unavoidable impurities such as hafnia (HfO2). The amount of hafnia as an unavoidable impurity varies greatly depending on the raw ore and manufacturing method, but an example is 2.0% by mass or less. In calculating composition-based values ​​such as composition and density in this embodiment, hafnia can be treated as zirconia (ZrO2) in the calculations.

[0078] Zirconia preferably contains a stabilizing element, and more preferably is zirconia in which the stabilizing element is in solid solution (hereinafter also referred to as "stabilizing element solid solution zirconia"). The stabilizing element preferably contains at least yttrium, and examples include one or more selected from the group consisting of yttrium, calcium, cerium, magnesium, praseodymium, ytterbium, erbium, and terbium, and more preferably one or more selected from the group consisting of yttrium, cerium, erbium, and terbium, and more preferably yttrium.

[0079] The amount of stabilizing elements in the composition should be such that the zirconia crystal phase is stabilized, for example, 0.1 mol% to 10 mol%. When the stabilizing element is yttrium, the amount of stabilizing elements (also referred to as "yttrium amount," etc., when the stabilizing element is yttrium, etc.) should be 2.5 mol% or more, 3 mol% or more, 3.5 mol% or more, 4 mol% or more, or 4.5 mol% or more, and also 8 mol% or less, 7 mol% or less, 6 mol% or less, or 5.5 mol% or less, with 2.5 mol% to 8 mol% or less, 3 mol% or more, or 6 mol% or less, 3.5 mol% to 6 mol% or less, or 4.5 mol% to 5.5 mol% or less being preferred. The method of this embodiment can produce a sintered body with light transmittance equivalent to that of a normal sintered body, even when sintering a composition with a high amount of stabilizing elements, such as a composition with an amount of 4.5 mol% to 6 mol%, or even 5.1 mol% to 5.8 mol% or less.

[0080] The composition of this embodiment preferably does not contain undissolved stabilizing elements, and more preferably oxides of stabilizing elements, and more preferably does not contain undissolved yttria (Y2O3). Whether or not a composition contains undissolved stabilizing elements can be confirmed by its XRD pattern. That is, if the XRD pattern of the composition does not contain an XRD peak of an oxide of a stabilizing element (e.g., Y2O3), it can be considered that it does not contain undissolved stabilizing elements.

[0081] The composition may contain one or more elements selected from the group consisting of aluminum, germanium, silicon, and lanthanum, further containing one or more elements selected from the group consisting of aluminum, germanium, and silicon (hereinafter also referred to as "additive elements"), further containing at least one of aluminum and germanium, and further containing aluminum. The composition does not have to contain additive elements.

[0082] The content of additive elements (hereinafter also referred to as "amount of additive elements," and in cases where the additive element is aluminum, the amount of additive elements is also referred to as "aluminum amount," etc.) is 0% by mass or more, greater than 0% by mass, 0.02% by mass or more, or 0.05% by mass or more, and can be exemplified as less than 0.2% by mass, 0.15% by mass or less, 0.1% by mass or less, or 0.07% by mass or less, with greater than 0% by mass and 0.2% by mass or less, or 0.05% by mass or more and 0.07% by mass or less being preferred.

[0083] The form of the additive elements in the composition is arbitrary. Examples include aluminum as alumina (Al2O3), germanium as germanium (Ge2O3), and silicon as silica (SiO2). Furthermore, examples include lanthanum being included in at least one form: solid solution in zirconia or as an oxide (La2O3).

[0084] The composition may contain elements that have the function of coloring zirconia (hereinafter also referred to as "coloring elements"). Examples of coloring elements include at least one of transition metal elements and lanthanide rare earth elements, and further, at least one of transition metal elements other than zirconium (Zr) and hafnium (Hf), and lanthanide rare earth elements. Examples of preferred coloring elements include one or more selected from the group consisting of iron (Fe), cobalt (Co), manganese (Mn), nickel (Ni), copper (Cu), titanium (Ti), chromium (Cr), praseodymium (Pr), neodymium (Nd), erbium (Er), terbium (Tb), and ytterbium (Yb); further, one or more selected from the group consisting of iron, cobalt, manganese, nickel, copper, titanium, chromium, and neodymium; further, one or more selected from the group consisting of iron, cobalt, titanium, manganese, praseodymium, erbium, and terbium; further, one or more selected from the group consisting of iron, cobalt, titanium, erbium, and terbium; and further, one or more selected from the group consisting of iron, cobalt, titanium, and erbium. It is preferable to include at least iron or terbium, and more preferably to include at least iron. Furthermore, praseodymium, ytterbium, erbium, and terbium function as coloring and stabilizing elements, respectively.

[0085] Particularly preferred coloring elements include two or more selected from the group consisting of iron, cobalt, titanium, and erbium, and further, one or more selected from the group consisting of cobalt, titanium, and erbium, and iron.

[0086] The coloring elements may be of any type and in any quantity depending on the desired color tone of the sintered body. The content of each coloring element (hereinafter also referred to as "amount of coloring element," and in the case of iron, etc., also referred to as "amount of iron, etc.") will differ depending on the type of coloring element, but examples of the content of each coloring element include 0% by mass or more, greater than 0% by mass, 0.002% by mass or more, or 0.02% by mass or more, and also 0.5% by mass or less, 0.2% by mass or less, or 0.1% by mass or less, with 0% by mass or more and 0.5% by mass or less, greater than 0% by mass and 0.5% by mass or less, and 0.002% by mass or more and 0.2% by mass or less being preferred.

[0087] Furthermore, the total amount of coloring elements can be exemplified as 0% to 0.5% by mass, greater than 0% to 0.5% by mass, 0.05% to 0.5% by mass, or 0.1% to 0.45% by mass.

[0088] The form of the coloring element included in the composition is arbitrary. The coloring element may be included as at least one of ions or compounds. Alternatively, the coloring element may be included in zirconia by solid solution.

[0089] The composition may contain a binder. Known binders used for molding ceramics can be used, and organic binders are preferred. The organic binder is one or more selected from the group consisting of polyvinyl alcohol, polyvinyl butyrate, wax, and acrylic resin, preferably polyvinyl alcohol and one or more acrylic resins, and more preferably acrylic resin. In this embodiment, the acrylic resin is a polymer containing at least one of acrylic acid esters and methacrylic acid esters. Specific acrylic resins include one or more selected from the group consisting of polyacrylic acid, polymethacrylic acid, acrylic acid copolymers, and methacrylic acid copolymers, as well as their derivatives. Specific binders include, for example, one or more selected from the group consisting of AS-1100, AS-1800, and AS-2000 (all product names, manufactured by Toagosei Co., Ltd.).

[0090] The amount of stabilizing elements in a composition can be determined as the molar ratio [mol%] of the stabilizing elements in oxide terms to the total amount of zirconium and stabilizing elements in oxide terms, the amount of additive elements can be determined as the mass ratio [mass%] of the additive elements in oxide terms to the composition in oxide terms, and the amount of coloring elements can be determined as the mass ratio [mass%] of the additive elements in oxide terms to the composition in oxide terms. For example, the composition of a zirconia composition mainly composed of yttrium and erbium as stabilizing elements, aluminum as an additive element, and iron and titanium as coloring elements can be determined as follows.

[0091] Mass of the composition =(ZrO2+Y2O3+Al2O3+Er2O3+Fe2O3+TiO2)[g] Stabilizing element amount (total) {(Er2O3+Y2O3)[mol] / (ZrO2+Y2O3+Er2O3)[mol]}×100 Yttrium quantity {Y2O3[mol] / (ZrO2+Y2O3+Er2O3)[mol]}×100 Erbium content (as a stabilizing element) {(Er2O3)[mol] / (ZrO2+Y2O3+Er2O3)[mol]}×100 Amount of added elements (aluminum amount) {Al2O3[g] / (ZrO2+Y2O3+Al2O3+Er2O3+Fe2O3+TiO2)[g]}×100 Coloring element content {(Er2O3+Fe2O3+TiO2)[g] / (ZrO2+Y2O3+Al2O3+Er2O3+Fe2O3+TiO2)[g]}×100 Iron content {Fe2O3[g] / (ZrO2+Y2O3+Al2O3+Er2O3+Fe2O 3 + TiO2)[g]} × 100 Titanium content {TiO2[g] / (ZrO2+Y2O3+Al2O3+Er2O3+Fe2O3 (+TiO2)[g]}×100 Erbium content (as a coloring element) {Er2O3[g] / (ZrO2+Y2O3+Al2O3+Er2O3+Fe2O 3 + TiO2)[g]} × 100 The oxide equivalents for each element are as follows: Zirconium = ZrO2, Yttrium = Y2O3, Calcium = CaO, Cerium = CeO2, Magnesium = MgO, and Praseodymium = Pr6O 11 Ytterbium is Yb2O3, erbium is Er2O3, and terbium is Tb7O 11 Aluminum is Al2O3, germanium is Ge2O3, silicon is SiO2, lanthanum is La2O3, iron is Fe2O3, cobalt is Co3O4, manganese is MnO2, nickel is NiO, copper is CuO, titanium is TiO2, chromium is Cr2O3, and neodymium is Nd2O3.

[0092] The composition may be any composition that can serve as a precursor to a sintered body, and may be one or more selected from the group consisting of zirconia powder, granular powder, molded body, and calcined body, and more preferably at least one of a molded body and a calcined body of zirconia, with a molded body or calcined body being preferred and a calcined body being more preferred.

[0093] Furthermore, if the composition is a calcined body, the manufacturing method of this embodiment may include a step of calcining the molded body of this embodiment (hereinafter also referred to as the "calcination step") prior to the first heating step.

[0094] Calcination can be any heat treatment that results in fused zirconia powder particles, such as heat treatment at a temperature below the sintering temperature of zirconia. The following conditions can be used for calcination: Calcination atmosphere: Oxidizing atmosphere, preferably air atmosphere Calcination temperature: 800°C or higher, 900°C or higher, or 950°C or higher, Below 1200℃, 1150℃ or below, or 1100℃ or below Pre-cooking time: 0.5 hours or more, or 1 hour or more, 5 hours or less or 3 hours or less

[0095] The calcination atmosphere may be the same as the sintering atmosphere, or it may be a different atmosphere.

[0096] If the composition is in powder form, the zirconia contained in the composition is preferably zirconia obtained by heat treatment of a zirconia sol, more preferably zirconia obtained by hydrolysis of a zirconium compound and then heat-treated, and even more preferably zirconia obtained by hydrolysis of zirconium oxychloride and then heat-treated.

[0097] The BET specific surface area of ​​the powder has a lower limit of 5 m². 2 / g or more, 6m 2 / g or more, 8m 2 / g or more, 9m 2 / g or more or 10m 2 It must be at least / g, and the upper limit is 15m 2 / g or less, 13m 2 / g or less or 11m 2 One example is that it is less than / g. 2 / g or more 15m 2 Preferably less than / g

[0098] The average particle size of the powder is 0.35 μm or larger or 0.40 μm or larger, and examples include 0.55 μm or smaller or 0.50 μm or smaller, with 0.35 μm or larger and 0.55 μm or smaller being preferred.

[0099] The crystalline phase of the powder preferably consists mainly of cubic and tetragonal phases, and more preferably consists mainly of cubic and tetragonal phases. The T+C phase ratio is 65% or more, 70% or more, or 75% or more, and may also be 100% or less, 99% or less, 98% or less, 95% or less, or 93% or less, with 65% to 100% or 75% to 93% being preferred.

[0100] The powder may be in granular form to improve flowability. The average granule size of the granular powder is 30 μm or more, 40 μm or more, or 50 μm or more, and examples include 80 μm or less or 60 μm or less, with 30 μm to 80 μm or 50 μm or 60 μm being preferred.

[0101] The bulk density of the granular powder in light packaging is 1.0 g / cm³. 3 or more, or 1.1 g / cm³ 3 That is all, and also 1.4 g / cm³ 3 The following or 1.3 g / cm³ 3 The following are listed, and 1.0 g / cm³ 3 More than 1.4g / cm 3 The following, or 1.1 g / cm³ 3 More than 1.3g / cm 3 The following are preferable.

[0102] If the composition is a molded body, the shape of the molded body can be at least one selected from the group consisting of cubic, rectangular, polyhedral, columnar, cylindrical, disc-shaped, and substantially spherical shapes, and it is acceptable for the shape to be similar to that of the target sintered body, taking into account thermal shrinkage due to sintering.

[0103] The density of the molded body is 2.8 g / cm³. 3 More than 2.9g / cm 3 or more, or 3.0 g / cm³3 That's all, and also 3.5 g / cm³ 3 Below, 3.4g / cm 3 Below, 3.3g / cm 3 Below, 3.2g / cm 3 The following or 3.1 g / cm³ 3 The following are listed, and 2.8 g / cm³ 3 More than 3.5g / cm 3 The following, or 3.0 g / cm³ 3 More than 3.1g / cm 3 The following are preferable.

[0104] If the composition is a calcined body, the shape of the calcined body can be at least one selected from the group consisting of cubic, rectangular, polyhedral, columnar, cylindrical, disc-shaped, and approximately spherical, and it is acceptable as long as it is a shape similar to the target sintered body, taking into account thermal shrinkage due to sintering.

[0105] The crystalline phase of the calcined body is preferably composed mainly of cubic and tetragonal phases, and more preferably of cubic and tetragonal phases. The T+C phase ratio is 75% or more, 80% or more, 90% or more, 95% or more, or 98% or more, and can also be 100% or less or 99% or less, with 75% to 100% or 98% to 100% being preferred.

[0106] The BET specific surface area of ​​the partially burned material is 5 m². 2 / g or more or 6m 2 It is 11m or more. 2 / g or less, 10m 2 / g or less or 9m 2 For example, it can be said that it is less than / g. 2 / g or more 11m 2 / g or less, 6m 2 / g or more 10m 2 / g or less, or 7m 2 / g or more 9m 2 / g is preferable.

[0107] The density of the calcined material is 2.9 g / cm³. 3 More than 3.0g / cm 3 or more, or 3.1 g / cm³3 The above is true, and also 3.5 g / cm³ 3 Below, 3.3g / cm 3 The following or 3.2 g / cm³ 3 The following are listed, and 2.9 g / cm³ 3 More than 3.5g / cm 3 Below 3.0g / cm 3 More than 3.3g / cm 3 The following, or 3.1 g / cm³ 3 More than 3.2g / cm 3 The following are preferable.

[0108] To reduce the likelihood of defects occurring during shape processing such as CAM machining, the Vickers hardness of the calcined body in this embodiment is set to 35 kgf / mm². 2 40 kgf / mm² or more 2 That's all, and also 100 kgf / mm 2 Below 80kgf / mm 2 Below, 70kgf / mm 2 Below, 55kgf / mm 2 The following or 50 kgf / mm 2 The following are some examples:

[0109] Prior to sintering, the calcined body can be processed into any desired shape using processing methods such as CAD / CAM machining. Thus, the calcined body used in the manufacturing method of this embodiment may be a calcined body in a processed state.

[0110] [Method for producing the composition] The composition used in the manufacturing method of this embodiment may be one or more selected from the group consisting of powders, granular powders, molded articles, and calcined articles obtained by known manufacturing methods. If the composition is in powder form, zirconia or zirconia containing stabilizing elements may be obtained by one or more methods selected from the group consisting of coprecipitation, hydrolysis, and sol-gel methods, preferably at least one of neutralization coprecipitation and hydrolysis, more preferably hydrolysis. If necessary, additive elements may be mixed with the obtained powder to form the composition used in the manufacturing method of this embodiment.

[0111] The composition may contain two or more stabilized element solid-solution zirconia with different amounts of stabilizing elements, or it may be a powder composition containing two or more stabilized element solid-solution zirconia with different amounts of stabilizing elements. A powder composition containing two or more stabilized element solid-solution zirconia with different amounts of stabilizing elements is obtained by mixing powders of two or more stabilized element solid-solution zirconia with different amounts of stabilizing elements. The mixing method may be any method that results in a uniform composition of the powder, and may include at least one of dry mixing and wet mixing, as well as wet mixing and mixing in an aqueous solvent, and may include mixing a slurry containing powder of stabilized element solid-solution zirconia.

[0112] If the composition is a molded body, the method for manufacturing the molded body is arbitrary, and the powder composition may be molded using a known ceramic molding method. Examples of molding methods include one or more selected from the group consisting of uniaxial pressing, cold isohydrographic pressing, slip casting, and injection molding. It is preferable that the molding method is at least one other than slip casting, more preferably at least one of uniaxial pressing and cold isohydrographic pressing, and even more preferably a molding method in which cold isohydrographic pressing is performed after uniaxial pressing. Examples of uniaxial pressing pressures include 15 MPa to 150 MPa, and examples of cold isohydrographic pressing pressures include 90 MPa to 400 MPa. The higher the pressure during molding, the higher the density of the molded body becomes until equilibrium is reached.

[0113] If the molded article contains a binder, a step to remove the binder, a so-called debindering step, may be included prior to calcination. The method of removing the binder is arbitrary, but examples include heat treatment in an air atmosphere at 400°C or higher but less than 800°C.

[0114] If the composition is a calcined body, a calcined body can be obtained by calcining the molded body in the same manner as the calcination process described above.

[0115] [Zirconia sintered body] The sintered body obtained by the manufacturing method of this embodiment (hereinafter also referred to as "the sintered body of this embodiment") will be described below. The composition of the sintered body in this embodiment may be the same as that of the composition described above or the calcined body.

[0116] The total light transmittance of the sintered body of this embodiment is 25% or more, 30% or more, or 35% or more, and can also be 55% or less, 53% or less, or 51% or less, and is preferably 25% or more and 55% or less, 30% or more and 53% or less, or 35% or more and 51% or less.

[0117] The sintered body of this embodiment preferably has light transmittance that gives the precursor similar to that of the sintered body the same visibility as that of a conventional sintered body. Examples of such light transmittance include a ratio of the total light transmittance of the sintered body of this embodiment to the total light transmittance of a conventional sintered body (hereinafter also referred to as the "transmittance ratio") of 0.95 or more or 0.96 or more, and also 1.05 or less or 1.00 or less, and can be described as 0.95 or more and 1.05 or less, or 0.96 or more and 1.00 or less.

[0118] In this embodiment, a typical sintered body is obtained by heating the material in an atmospheric environment from room temperature to 1500°C at a heating rate of 10°C / min, holding it at 1500°C for 120 minutes, and then sintering it from 1500°C to room temperature at a cooling rate of 10°C / min.

[0119] The biaxial bending strength of the sintered body of this embodiment can be exemplified as being between 800 MPa and 1400 MPa. The sintered body of this embodiment, with a biaxial bending strength of 800 MPa or more, is also suitable for connecting bridges with four or more teeth based on JIS T 6526. The biaxial bending strength can be 830 MPa or more, or 900 MPa or more, and also 1300 MPa or less, 1200 MPa or less, or 1100 MPa or less, with 830 MPa to 1300 MPa or 900 MPa to 1100 MPa being preferable.

[0120] The shape of the sintered body in this embodiment can be at least one selected from the group consisting of cubic, rectangular, polyhedral, columnar, cylindrical, disc-shaped, and substantially spherical shapes, and it is preferable that the shape is suitable for use as a dental material, and even more so as a dental prosthetic material.

[0121] The sintered body of this embodiment is preferably a sintered body that can be used as a dental material, and more preferably as a dental prosthetic material. [Examples]

[0122] The embodiment will be described in detail below with reference to examples. However, this embodiment is not limited to these examples.

[0123] (composition analysis) The composition of the composition was determined by ICP analysis.

[0124] (BET specific surface area) The BET specific surface area was measured using an automatic specific surface area measuring device (device name: Tristar II 3020, manufactured by Shimadzu Corporation) in accordance with JIS R 1626, under the following conditions, using the BET multi-point method (5 points). Adsorption medium: N2 Adsorption temperature: -196℃ Pretreatment conditions: Degassing treatment at 250°C for at least 1 hour in an air atmosphere.

[0125] If the sample to be measured was a calcined body, prior to measurement, the calcined body was processed into a rectangular parallelepiped shape of 5 mm x 5 mm x 16 mm, and then all surfaces of the rectangular parallelepiped were polished using sandpaper with a grit of #400 in accordance with JIS R 6001-2.

[0126] (Average particle size) The average granule size was measured by placing a granular powder sample into a Microtrac particle size analyzer (instrument name: MT3100II, manufactured by Microtrac-Bell). The average granule size was defined as the particle size at which the cumulative volume reached 50%.

[0127] (Crystal phase and T+C phase ratio) The crystalline phase was identified by XRD measurement using an X-ray diffractometer (instrument name: Ultima IV, manufactured by RIGAKU Corporation) under the following conditions. Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 2° / min Measurement range: 2θ = 26° ~ 33° 2θ = 72°~76° Acceleration voltage / current: 40mA / 40kV Divergence vertical limiting slit: 10mm Divergence / Induction Slit: 1° Light-receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185mm

[0128] Prior to the measurement, the surface of the calcined body was polished using #400 grit sandpaper in accordance with JIS R 6001-2, and then lapped using a 3 μm grit diamond abrasive.

[0129] Crystal phase identification and area intensity calculation of each crystal plane were performed using the analysis program attached to the X-ray diffractometer (program name: Integrated Powder X-ray Analysis Software PDXL Ver.2.2, manufactured by RIGAKU Corporation), which performed smoothing and background removal processing. The XRD pattern after this processing was then profile-fitted using a segmented pseudo-Voigt function.

[0130] The T+C phase ratio was determined from the XRD pattern of the calcined body of this embodiment using the formula described above.

[0131] (Average cooling rate) During the rapid cooling process, a thermocouple thermometer (device name: testo735-1, manufactured by Testo) was placed in contact with the surface of the sintered body, and the time it took to reach 400°C from the cooling temperature was measured. The average cooling rate was defined as the value obtained using {(cooling temperature - 400) [°C] / time from cooling temperature to 400°C [minutes]}.

[0132] (Green body density) The mass of the green body sample was measured with a balance, and the volume was determined from the dimensions measured with a caliper. The green body density was determined from the obtained mass and volume.

[0133] (Total light transmittance) The total light transmittance of the sample was measured by a method according to JIS K 7361. The total light transmittance was measured by irradiating the measurement sample with a standard light source D65 and detecting the light beam transmitted through the measurement sample with an integrating sphere. A haze meter (apparatus name: Haze meter NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) was used for the measurement.

[0134] For the measurement sample, a disk-shaped sintered body with a diameter of 20 mm, a sample thickness of 1.0 ± 0.1 mm, and mirror-polished until the surface roughness Ra of both surfaces was ≦ 0.02 μm was used.

[0135] (Biaxial flexural strength) The biaxial flexural strength was measured by a method according to JIS T 6526. The measurement was performed 10 times, and the average value was determined. The measurement was performed on a circular sintered body sample with a diameter of 14.5 mm ± 0.5 and a thickness of 1.25 mm ± 0.05 mm, and was carried out with a support circle radius of 6 mm and a punch radius of 0.7 mm. The crosshead speed was 0.5 mm / min.

[0136] Synthesis Example 1 After filling 3 g of commercially available zirconia powder (product name: Zpex, manufactured by Tosoh Corporation) into a mold with an inner diameter of 25 mm, uniaxial compression pressing was performed at a pressure of 49 MPa. After molding, CIP treatment was performed at a pressure of 196 MPa to obtain a disk-shaped molded body with a diameter of 25 mm.

[0137] The obtained molded body was heated to 1000 °C at a heating rate of 50 °C / hour, held at 1000 °C for 1 hour, and a green body composed of yttrium-stabilized zirconia containing alumina with a yttrium content of 3.0 mol% and an aluminum amount of 0.05 mass% was obtained, and this was used as the green body of this synthesis example. The BET specific surface area of the green body of this Synthesis Example 1 was 9.1 m 2It was / g.

[0138] Synthesis Example 2 Except for using commercially available zirconia powder (product name: Zpex4, manufactured by Tosoh Corporation), a calcined body was obtained in the same manner as in Synthesis Example 1, containing alumina with an aluminum content of 0.05 mass%, and the remainder being yttrium content of 4.0 mol%, consisting of yttrium-stabilized zirconia. This calcined body was used as the calcined body for this synthesis example. The BET specific surface area of ​​the calcined body for this synthesis example was 7.4 m². 2 It was / g.

[0139] Synthesis Example 3 A mixed powder was obtained by mixing commercially available zirconia powders (Zpex4, Zpex4-Yellow, and Zpex-Gray, all manufactured by Tosoh Corporation) in a mass ratio of Zpex4:Zpex4-Yellow:Zpex-Gray = 30:60:10. Except for using the obtained powder, a calcined body was obtained from yttrium-stabilized zirconia containing alumina, iron oxide, and cobalt oxide, with a yttrium content of 4.0 mol%, aluminum content of 0.05 mass%, iron content of 0.095 mass%, and cobalt content of 0.0045 mass%, and this calcined body was used as the calcined body for this synthesis example. The BET specific surface area of ​​the calcined body for this synthesis example was 7.5 m². 2 It was / g.

[0140] Synthesis Example 4 Yttrium-stabilized zirconia powder with a yttrium content of 2.5 mol% (BET specific surface area: 14.1 m²) 2 A slurry of yttrium (1 / g) (hereinafter also referred to as "2.5Y slurry"), and yttrium-stabilized zirconia powder with a yttrium content of 5.5 mol% (BET specific surface area: 10.9 m²). 2 A slurry of 5.5 / g (hereinafter also referred to as "5.5Y slurry") was mixed to obtain a mixed slurry with a yttrium content of 5.2 mol%. The mixed slurry was spray-dried at 180°C to obtain yttrium-stabilized zirconia granules with a yttrium content of 5.2 mol%. The BET specific surface area of ​​the obtained granules was 11.2 m². 2 The weight per gram and the average granule size were 46 μm.

[0141] Except for using the obtained granular powder, a calcined yttrium-stabilized zirconia with a yttrium content of 5.2 mol% was obtained using the same method as in Synthesis Example 1, and this was used as the calcined body for this synthesis example.

[0142] Synthesis Example 5 A slurry containing 10% by mass of iron oxide (Fe2O3) powder, 11.7% by mass (4.1 mol%) of erbium-stabilized zirconia powder, and 10% by mass of 2.5Y slurry and 5.5Y slurry, and a slurry containing 45% by mass of erbium-stabilized zirconia powder with an erbium content of 11.7% by mass (4.1 mol%) were mixed to obtain a mixed slurry with a yttrium content of 5.0 mol%, an iron content of 0.072% by mass, and an erbium content of 0.34% by mass (0.12 mol%). A granular powder containing iron oxide, erbium-stabilized zirconia, and yttria-stabilized zirconia was obtained using the same method as in Synthesis Example 4, except that the obtained mixed slurry was used. The BET specific surface area of ​​the obtained granular powder was 11.4 m². 2 The average granule size per g was 47 μm.

[0143] Except for using the obtained granular powder, the same method as in Synthesis Example 1 was used to obtain a calcined body containing 5.0 mol% yttrium, 0.072 mass% iron, and 0.34 mass% (0.12 mol%) erbium, and which included iron oxide, erbium-stabilized zirconia, and yttrium-stabilized zirconia. This calcined body was used as the calcined body for this synthesis example.

[0144] Synthesis Example 6 In addition to the 2.5Y slurry and the 5.5Y slurry, a slurry containing 10% by mass of iron oxide powder, a slurry containing 10% by mass of cobalt oxide (Co3O4) powder, and a slurry containing 10% by mass of titanium oxide (TiO2) were mixed so that the yttrium amount was 5.2 mol%, the iron amount was 0.105% by mass, the cobalt amount was 0.0063% by mass, and the titania amount was 0.0314% by mass, to obtain a mixed slurry. Except for using the obtained mixed slurry, in the same manner as in Synthesis Example 4, yttrium amount was 5.2 mol%, iron amount was 0.105% by mass, cobalt amount was 0.0063% by mass, and titanium amount was 0.0314% by mass, and a granular powder of yttria-stabilized zirconia containing iron oxide, cobalt oxide and titanium oxide was obtained. The BET specific surface area of the obtained granular powder was 11.0 m 2 / g and the average particle diameter was 48 μm.

[0145] Except for using the obtained granular powder, in the same manner as in Synthesis Example 1, yttrium amount was 5.2 mol%, iron amount was 0.105% by mass, cobalt amount was 0.0063% by mass, and titanium amount was 0.0314% by mass, and a calcined body of yttria-stabilized zirconia containing iron oxide, cobalt oxide and titanium oxide was obtained, and this was used as the calcined body of this synthesis example.

[0146] The evaluation results of the calcined bodies obtained in each synthesis example are shown in the following table.

[0147]

Table 1

[0148] <Sintering pattern> Using a sintering furnace equipped with a silicon carbide heater, the temperature was raised from room temperature in an air atmosphere according to the sintering pattern in the following table, and the calcined bodies obtained in each synthesis example were sintered at normal pressure. After cooling to T3, the sintered body after sintering was taken out of the sintering furnace and cooled to 400 °C by blowing air onto the sintered body in an air atmosphere.

[0149]

Table 2

[0150] Reference example The calcined bodies of Synthesis Examples 1 to 6 were sintered by normal sintering of the sintering pattern (P16) to obtain normally sintered bodies, which were then used as Reference Examples 1 to 6. The results are shown below.

[0151] [Table 3]

[0152] Reference Examples 1, 2, and 4 confirmed that increasing the yttrium content resulted in higher total light transmittance and improved light transmission. Furthermore, it was confirmed that sintered bodies containing coloring elements exhibited lower total light transmittance compared to sintered bodies without coloring elements.

[0153] Examples 1 to 6 The calcined bodies of synthesis examples 1 to 6 were each sintered according to sintering pattern (P1) to obtain sintered bodies. The results are shown below.

[0154] [Table 4]

[0155] The sintered bodies of the examples containing 3 mol% to 5.2 mol% yttrium had a transmittance ratio of 0.97 to 1.03, exhibiting light transmittance comparable to that of ordinary sintered bodies. This confirms that the manufacturing method of the examples can produce sintered bodies with light transmittance comparable to that of ordinary sintered bodies, regardless of the yttrium content, and even when the yttrium content is 4.5 mol% or more.

[0156] Furthermore, the three-point bending strength of the sintered body with a yttrium content of 5.2 mol% in Example 4 was 836 MPa, confirming that it possesses the strength required for ceramics used in prosthetic devices with four or more teeth, as specified in JIS T 6526.

[0157] Examples 7 to 10 and Comparative Examples 1 to 4 The calcined bodies of Synthesis Example 2 or 4 were sintered according to the following sintering patterns to obtain sintered bodies. The results are shown in the table below.

[0158] [Table 5]

[0159] When the HR2 was 200°C / min, a sintered body with light transmittance equivalent to that of a normal sintered body was obtained when the yttrium content was 4 mol%, whereas when the yttrium content was 5.2 mol%, it was confirmed that the light transmittance was significantly lower than that of a normal sintered body (Comparative Examples 2 and 4). Conversely, when the HR2 was 30°C / min, a sintered body with light transmittance equivalent to that of a normal sintered body was obtained when the yttrium content was 5.2 mol%, while when the yttrium content was 4 mol%, it was confirmed that the light transmittance was significantly lower than that of a normal sintered body (Comparative Examples 1 and 3). Furthermore, with a composition containing 4 mol% yttrium, the light transmittance of the resulting sintered body increased with increasing HR2, while with a composition containing 5.2 mol% yttrium, the light transmittance of the resulting sintered body decreased with increasing HR2, confirming that the relationship between HR2 and light transmittance differs depending on the amount of yttrium.

[0160] Examples 11 to 16, and Comparative Examples 5 and 6 The calcined bodies of Synthesis Example 2 or 4 were sintered according to the following sintering patterns to obtain sintered bodies. The results are shown in the table below.

[0161] [Table 6]

[0162] Regardless of the amount of yttrium, it was confirmed that the transparency of the sintered body decreased significantly compared to a normal sintered body when it was not held at T2 (Comparative Examples 5 and 6). Furthermore, while the transparency of the sintered body obtained from a composition with 4 mol% yttrium increased with decreasing holding time, the transparency of the sintered body obtained from a composition with 5.2 mol% yttrium increased with increasing holding time, confirming that the effect of holding time on transparency differs depending on the amount of yttrium.

[0163] Examples 17 to 20, and Comparative Examples 7 and 8 The calcined bodies of Synthesis Example 2 or 4 were sintered according to the following sintering patterns to obtain sintered bodies. The results are shown in the table below.

[0164] [Table 7]

[0165] When T1 is set to 1400°C, a sintered body with light transmittance equivalent to that of a normal sintered body is obtained when the yttrium content is 4 mol%, whereas when the yttrium content is 5.2 mol%, it was confirmed that the light transmittance is significantly reduced compared to a normal sintered body.

[0166] Examples 21 to 26 The calcined bodies of Synthesis Example 2 or 4 were sintered according to the following sintering patterns to obtain sintered bodies. The results are shown in the table below.

[0167] [Table 8]

[0168] It was confirmed that, within the T2 range of 1530°C to 1560°C, light transmittance similar to that of a normal sintered body can be obtained, regardless of the yttrium content.

[0169] Furthermore, the three-point bending strength of the sintered body with a yttrium content of 5.2 mol% in Example 24 was 955 MPa, confirming that it possesses the strength required for ceramics used in prosthetic devices with four or more teeth, as specified in JIS T 6526:2018.

[0170] Examples 26 to 31 The calcined bodies of Synthesis Example 2 or 4 were sintered according to the following sintering patterns to obtain sintered bodies. The results are shown in the table below.

[0171] [Table 9]

[0172] In the HR range of 150°C / min to 300°C / min, it was confirmed that a sintered body with light transmittance equivalent to that of a normal sintered body can be obtained, regardless of the yttrium content.

Claims

1. It contains stabilizing elements, with a stabilizing element content of 2.5 mol% to 5.2 mol%, and has at least one of cubic or tetragonal phases as the main phase, and a BET specific surface area of ​​5 m². ２ A method for producing a sintered zirconia body containing a stabilizing element, comprising: a first heating step of heating a calcined zirconia body having a concentration of 1 / g or more from a heating start temperature to a first target temperature of 800°C to 1150°C at a heating rate of 150°C / min or more; a second heating step of heating from the first target temperature to a second target temperature of 1400°C to less than 1580°C at a heating rate of 50°C / min to 100°C / min; and a holding step of holding the body at the second target temperature.

2. The manufacturing method according to claim 1, wherein the holding time in the holding step is less than 20 minutes.

3. The manufacturing method according to claim 1 or 2, wherein the difference between the second temperature reached and the first temperature reached is 300°C or more and 600°C or less.

4. The manufacturing method according to claim 1 or 2, wherein the rate of heating up to the second temperature is 0.15 or more and 1.0 or less relative to the rate of heating up to the first temperature.

5. The manufacturing method according to claim 1 or 2, wherein the temperature at which the heating starts is any temperature from room temperature to 500°C.

6. The manufacturing method according to claim 1 or 2, further comprising a cooling step of cooling the sintered body from the second attained temperature to any cooling temperature of 800°C to 1200°C and removing the sintered body from the sintering furnace.

7. The manufacturing method according to claim 1 or 2, wherein the stabilizing element is one or more selected from the group consisting of yttrium, calcium, cerium, magnesium, praseodymium, ytterbium, erbium, and terbium.

8. The manufacturing method according to claim 1 or 2, wherein the calcined body contains at least one coloring element from a transition metal element other than zirconium and hafnium, and from a lanthanide rare earth element.

9. The manufacturing method according to claim 8, wherein the coloring element is one or more selected from the group consisting of iron (Fe), cobalt (Co), manganese (Mn), nickel (Ni), copper (Cu), titanium (Ti), chromium (Cr), praseodymium (Pr), neodymium (Nd), erbium (Er), terbium (Tb), and ytterbium (Yb).

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